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ZOOLOGICAL ARTICLES

3RATORY

LIBRARY

WOODS HOLE, MASS.
W. H. 0. I.

ZOOLOGICAL ARTICLES

CONTRIBUTED TO THE "ENCYCLOPEDIA BRITANNICA"

BY

E. RAY LANKESTER, M.A., LL.D., F.R.S.

DEPUTY LINACRE PROFESSOR IN THE UNIVERSITY OF OXFORD, AND HOK. FELLOW OF EXETER COLLEGE
PRESIDENT OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM ;

HON. MEMBER OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY;
CORRESPONDING MEMBER OF THE ACADEMY OF SCIENCES OF PHILADELPHIA.

TO WHICH ARE ADDED KINDRED ARTICLES BY

W. JOHNSON SOLLAS, LL.D., F.R.S.

PROFESSOR OF GEOLOGY IN TRINITY COLLEGE, DUBLIN.

LUDWIG VON GRAFF, PH.D.

I'ROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF GRAZ, AUSTRIA.

A. A. AV. HUBRECHT, PH.D., LL.D.

PROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF UTRECHT.

A. G. BOURNE, D.Sc.

PROFESSOR OF BIOLOGY IN THE PItESIDENCY COLLKGF-, MADRAS.

W. A. HERDMAN, D.Sc.

PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY COLLEGE, LIVERPOOL.

EDINBURGH: ADAM & CHAELES BLACK
NEW YORK: CHARLES SCRIBNER'S SONS

MDCCCXCI

I

PREFACE.

T HAVE been anxious to render the articles on various groups of Animals written by
me for the Encyclopaedia Britannica more readily accessible to the University
student than they are when bound up in the large volumes of that great work. The
Publishers have very kindly met my wishes in this respect by consenting to issue the
present reprint. With my articles on Protozoa, Hydrozoa, Mollusca, Polyzoa, and
Vertebrata, are here included, by the kind consent of the authors, the article on Sponges
by Professor Sollas, that on Planarians by Professor von Graff, that on Nemertines by
Professor Hubrecht, that on Rotifera by Professor Bourne, and that on Tunicata by
Professor Herdman. The volume thus forms a treatise on a considerable section of the
animal kingdom. Obviously it does not profess to be a complete handbook. Since the
articles are reprinted from the original plates, and issued at a low price, it has not been
possible to introduce any large additions into the text. Here and there an error, due to
oversight, has been corrected, and one or two new figures have been added, rendering the
work more complete. The chief additions are the woodcut illustrating recent discoveries
concerning the Dinoflagellata (p. 37) ; the note by Professor Sollas on the classification of
Monaxonida (p. 39); the woodcut of Scyphomedusre from the Deep-Sea (p. 57); the
woodcut fig. 19 on p. 107, which replaces a similar but incorrect figure in the original
article, and the woodcut, fig. IA on p. 159, showing forms connecting the Eupolyzoa and
other Gephyrsea.

There are one or two matters, by way of addition to or correction of my own articles,
which this preface gives me the opportunity of mentioning.

In regard to the Protozoa, the reader should note that Professor Butschli's treatise in
Bronn's Thicrreich is now completed. He has rejected the classification of the Ciliata.
which we owe to Stein, and adopts the following Branch A. Gymnostoma ( = Holotricha
with chitiuised pharynx, Prorodon, Trachelius, &c.) ; Branch B. Trichostoma ( = the
remaining Ciliata, all of which have the pharynx ciliated, if present). The Trichostoma
are divided into two classes the Aspirotricha, and the Spirotricha. The Aspirotricha
are the rest of the Holotricha of Stein, not comprised in the Gymnostoma of this classifi-

VI PREFACE

cation. The Spirotricha are characterised by all possessing the adoral " heterotrichal " band
of large cilia ; they are divided into the sub-classes Heterotricha, Hypotricha, Peritricha,
and Oligotricha. The two first of these groups correspond with Stein's groups of the same
names, whilst the Peritricha of Stein are now divided into Peritricha and Oligotricha, the
latter sub-class being formed for such genera as Halteria, Strombidium, and Tintinnus. I
consider Blitschli's classification an improvement upon Stein's, with the doubtful exception
of the distinct position assigned to the Oligotricha.

In regard to the Hydrozoa, the most important additions to knowledge since the date
of the article are to be found in the large and richly-illustrated monographs by Haeckel
(System der Medusen, Jena, 1879-1880 ; "Report on the Deep-Sea Medusse," Challenger
Reports, vol. iv., 1882; "Reports on the Deep-Sea Siphonophora," Challenger Reports^
vol. xxviii., 1888), and in the remarkable researches of Weissman on the origin of the
sexual products (Enstelmng der Sexnahellen bei der Hydromedusen, Jena, 1883). The
student who takes in hand the actual examination of a specimen of Aurelia aurita by
aid of the description given of it in the article Hydrozoa, should also refer to the plates of
Ehrenberg's account of this animal (Physikalische Abhandlungen der Konigl. Alxtd. d.
Wissensch., Berlin, 1835), and Mr Min chin's brief but valuable paper on the enclosure of
the embryos in minute brood pouches formed by sacculation of the grooves of the oral
lobes (Proc. Zool. Soc., 1889, No. xxxix.).

If I were rewriting the article Mollusca, I should adopt the conclusion of my friend
and former pupil, Dr Paul Pelseueer, of Ghent, and remove the Pteropoda from association
with the Cephalopoda, not to maintain them as a distinct class, but to place them, as he
has done, among the Palliate or Tectibranchiate Opisthobranchiate Gastropoda, to which, it
seems, they bear the same relation as do the Natantia to the Azygobranchiate Streptoneura.
It appears that the Thecosomate Pteropods are nearly related to the Bullidse and Torna-
tellidse, whilst the Gymnosomate forms are derivable from the Aplysiidse. A careful study
of the nervous system convinced Dr Pelseneer that the sucker-bearing lobes of such
Gymnosomate Pteropods as Pneumodermon are really cephalic in nature, and innervated
from the cerebral ganglion, whilst the sucker-bearing lobes of the Cephalopoda are produc-
tions of the foot, and are convincingly demonstrated by Pelseneer (as maintained by me in
the article " Mollusca ") to be innervated by the pedal ganglia. The remarkable coincidence
in the Pteropoda and Cephalopoda of adoral appendages provided with suckers which had
been, to my mind, the chief ground for supposing a genetic relationship between these
two sets of forms, proves to be a case of homoplasy. 1 It is, indeed, a very striking case of
the parallelism of genetically distinct organs. The whole of this question is ably treated
by Pelseneer in Part III. of his " Report on the Pteropoda," published in vol. xxiii. of the
Challenger Reports, 1888. The student of molluscan anatomy should not fail to read this

1 The reader is referred for an explanation of this term, and a discussion of the phenomena concerned, to my article
" On the use of the term Homology in Modern Zoology, and the distinction between Homogenetic and Homoplastic
Agreements," Ann. and May. Nat. Hint., 1870.

PREFACE. Vll

clear and well-illustrated discussion of the structure of the Pteropoda, and of the inferences
which may be drawn therefrom as to their affinities.

Iii regard to the article Polyzoa, I may mention that I think it preferable to make use
of the established term "Gephyrsea" in place of that introduced in this article, viz.,
" Podaxonia," The Gephyreea, then, include the Sternaspidomorpha, Echiuromorpha,
Sipunculomorpha, Phoronidomorpha, Polyzoa (Eupolyzoa of the article), Brachiopoda, and
Pterobranchia, Concerning the affinities of the first four of these classes with one another,
there is little doubt : as to the affinities of the last three with one another, and with the
first four we are still in a very uncertain state, and are likely to remain so for some time,
owing to the absence of satisfactory embryological data and the difficulty of obtaining such.

The subject matter of the article Vertebra ta is much more extensive than that of the
other chapters, and, owing to limited space, is treated in a much more general way than is
the case with the latter. In regard to the Craniata, the intention was to give only a sketch
of leading features which should be supplemented by the study of such works as Gegenbaur's
Comparative Anatomy, Wiedersheim's Anatomy of Vertebrates, and the special articles on
Fishes, Eeptiles, Birds, and Mammals, written for the Encyclopaedia by eminent autho-
rities on those groups. The treatment of the Cephalochorda (Arnphioxus) and its relations
to the Urochorda is a little more complete, and I therefore take occasion to refer the reader
to recent publications, in which our knowledge of this most interesting member of the
Vertebrate group has been largely extended. They are Contributions to the Know-
ledge of Rhabdopleura and Amphioxus (ubique citata), by E. Ray Lankester (London:
J. & A. Churchill, 1889); "The Development of the Atrial Chamber of Amphioxus," by
E. Ray Lankester and Arthur Willey, in the Quart. Jour, of Mic. Sci., vol. xxxi., 1890 ;
"The Later Larval Development of Amphioxus," by Arthur Willey, B.Sc., in the same
Journal, vol. xxxii. ; and "The Excretory Organs of Amphioxus," by F. E. Weiss, B.Sc.,
also in the Quart. Jour, of Mic. Sci., vol. xxxi.

The article " Sponges," by Professor Sollas, contains the only summary account of the
Porifera written since the recent extraordinary advances in our knowledge of this group.
Its incorporation in the present volume cannot fail to be welcome to students. In
Professor Bourne's article on Rotifera are given the only extant woodcuts of the important
genus Pedalion. This most important form is not figured or discussed in any other general
treatise accessible to students. The articles on Planarians and Nemertiues, by Professor
von Graff and Professor Hubrecht respectively, are brief summaries of what is known,
written by the chief living authority on each group.

E. RAY LANKESTER.

OXFORD, December 1890.

CONTENTS.

PAGE

PROTOZOA, . . . !

SPONGES, 39

HYDROZOA, . 57

PLANARIANS, 77

NEMERTINES, 83

ROTIFERA, . 89

MOLLUSCA, . 95

POLYZOA, 169

VERTEBRATA, 173

TUNICATA, 185

ZOOLOGICAL ARTICLES.

PKOTOZOA

PROTOZOA is the name applied to the lowest grade of
the animal kingdom, and originated as a translation
of the German term "Urthiere." Whilst at first used
some forty years ago in a vague sense, without any strict
definition, so as to include on the one hand some simple
organisms which are now regarded as plants and on the
other some animals which are now assigned a higher place
in the animal series, the term has within the last twenty
years acquired a very clear signification.

The Protozoa are sharply and definitely distinguished
from all the rest of the animal kingdom, which are known
by the names " Metazoa " or " Enterozoa." They are
those animals which are structurally single "cells" or
single corpuscles of protoplasm, whereas the Enterozoa
consist of many such units arranged definitely (in the first
instance) in two layers an endoderin or enteric cell-layer
and an ectoderm or deric cell-layer around a central
cavity, the enteron or common digestive cavity, which is
in open communication with the exterior by a mouth.

The Protozoa are then essentially unicellular animals.
The individual or person in this grade of the animal king-
dom is a single cell ; and, although we find Protozoa which
consist of aggregates of such cells, and are entitled to be
called " multicellular," yet an examination of the details
of structure of these cell-aggregates and of their life-
history establishes the fact that the cohesion of the cells
in these instances is not an essential feature of the life of
such multicellular Protozoa but a secondary and non-essen-
tial arrangement. Like the budded " persons " forming,
when coherent to one another, undifferentiated " colonies "
among the Polyps and Corals, the coherent cells of a com-
pound Protozoon can be separated from one another and
live independently ; their cohesion has no economic signifi-
cance. Each cell is precisely the counterpart of its neigh-
bour ; there is no common life, no distribution of function
among special groups of the associated cells, and no cor-
responding differentiation of structure. As a contrast to
this we find even in the simplest Enterozoa that the cells
are functionally and structurally distinguishable into two
groups those which line the enteron or digestive cavity
and those which form the outer body wall. The cells of
these two layers are not interchangeable ; they are funda-
mentally different in properties and structure from one
another. The individual Enterozoon is not a single cell ;
it is an aggregate of a higher order consisting essentially
of a digestive cavity around which two layers of cells are

disposed. The individual Protozoon is a single cell; a
number of these individuals may, as the result of the pro-
cess of fission (cell-division), remain in contact with one
another, but the compound individual which they thus
originate has not a strong character. The constituent
cells are still the more important individualities ; they
never become differentiated and grouped in distinct layers
differing from one another in properties and structure ;
they never become subordinated to the individuality of
the aggregate produced by their cohesion ; hence we are
justified in calling even these exceptional aggregated
Protozoa unicellular.

By far the larger number of Protozoa are absolutely
single isolated cells, which, whenever they duplicate them-
selves by that process of division common to these units
of structure (whether existing as isolated organisms or as
constituents of the tissues of plants or of animals), separ-
ate at once into two distinct individuals which move away
from one another and are thenceforward strangers.

Whilst it is easy to draw the line between the Protozoa
and the Enterozoa or Metazoa which lie above them, on
account of the perfectly definite differentiation of the cells
of the latter into two primary tissues, it is more difficult to
separate the Protozoa from the parallel group of unicellular
plants.

Theoretically there is no difficulty about this distinction.
There is no doubt that organisms present themselves to us
in two great series starting in both cases from simple
unicellular forms. The one series, the plants, can take up
the carbon, hydrogen, oxygen, and nitrogen necessary to
build up their growing protoplasm from mineral com-
pounds soluble in water, compounds which constitute the
resting stage of those elements in the present physical
conditions of our planet. Plants can take their nitrogen
in the form of ammonia or in the form of nitrates and
their carbon in the form of carbonic acid. Accordingly
they require no mouths, no digestive apparatus ; their
food being soluble in water and diffusible, they absorb at
all or many points of their surface. The spreading diffuse
form of plants is definitely related to this fact. On the
other hand the series of organisms which we distinguish
as animals cannot take the nitrogen, necessary to build up
their protoplasm, in a lower state of combination than it
presents in the class of compounds known as albumens ;
nor can they take carbon in a lower state of combination
i than it presents when united with hydrogen or with

A

PROTOZOA

hydrogen and oxygen to form fat, sugar, and starch.
Albumens and fats are not soluble in water and diffusible ;
they have to be seized by the animal in the condition
of more or less solid particles, and by chemical processes
superinduced in the living protoplasm of the animal by
the contact of these particles they are acted upon, chemic-
ally modified, and rendered diffusible. Hence the animal
is provided with a mouth and a digestive cavity, and with
organs of locomotion and prehension by which it may search
out and appropriate its scattered nutriment. Further the
albumens, fats, sugars, and starch which are the necessary
food of an animal are not found in nature excepting as
the products of the life of plants or of animals ; accord-
ingly all animals are in a certain sense parasitic upon
either plants or other animals. It would therefore seem
to be easy to draw the line between even the most minute
unicellular plants and the similarly minute unicellular
animals assigning those which feed on the albumens, &c.,
of other organisms by means of a mouth and digestive
apparatus to the animal series, and those which can appro-
priate the elements of ammonia, nitrates, and carbonates
to the plants.

Such absolute distinctions lending themselves to sharp
definitions have, however, no place in the organic world ;
and this is found to be equally true whether we attempt
to categorically define smaller groups in the classification
of plants and animals or to indicate the boundaries of the
great primary division which those familiar names imply.
Closely allied to plants which are highly and specially
developed as plants, and feed exclusively upon ammonia,
nitrates, and carbonates, we find exceptionally modified
kinds which are known as " insectivorous plants " and are
provided with digestive cavities (the pitchers of pitcher-
plants, &c.), and actually feed by acting chemically upon
the albumens of insects which they catch in these diges-
tive receptacles. No one would entertain for a moment
the notion that these insectivorous plants should be con-
sidered as animals. The physiological definition separat-
ing plant from animal breaks down in their case ; but the
consideration of the probable history of their evolution as
indicated by their various details of structure suffices at
once to convince the most sceptical observer that they
actually belong to the vegetable line of descent or family
tree, though they have lost the leading physiological char-
acteristic which has dominated the structure of other
plants. In this extreme case it is made very obvious that
in grouping organisms as plants or as animals we are not
called upon to apply a definition but to consider the
multifarious evidences of historical evolution. And we
find in the case of the Protozoa and the Protophyta that
the same principle holds good, although, when dealing
with extremely simple forms, it becomes much more diffi-
cult to judge of the genetic relationship of an organism in
proportion as the number of detailed points of possible
agreement with and divergence from other forms to which
it may be supposed to be related are few.

The feeding of plants upon carbonic acid is invariably
accompanied by the presence of a peculiar green-colouring
matter chlorophyll. In virtue of some direct or indirect
action of this chlorophyll the protoplasm of the plant is
enabled to seize the carbon of the mineral world the car-
bon which has sunk to the lowest resting stage of combina-
tion and to raise it into combination with hydrogen and
oxygen and ultimately with nitrogen. There are plants
which have no chlorophyll and are thus unable to feed
upon carbonic acid. They are none the less plants since
they agree closely with particular chlorophyll-bearing
plants in details of form and structure, mode of growth
and reproduction. A large series of these are termed
Fungi. Though unable to feed on carbonic acid, they do

not feed as do animals. They can take their carbon from
acetates and tartrates, which animals cannot do, and their
nitrogen from ammonia. Even when it is admitted that
some of these colourless plants, such as the Bacteria
(Schizomycetes), can act upon albumens so as to digest
them and thus nourish themselves, it is not reasonable to
place the Bacteria among animals, any more than it would
be reasonable so to place Nepenthes, Sarracenia, and
Drosera (insectivorous Phanerogams). For the structure
and mode of growth of the Bacteria is like that of well-
known chlorophylligerous minute Algaj from which they
undoubtedly differ only in having secondarily acquired
this peculiar mode of nutrition, distinct from that which
has dominated and determined the typical structure of
plants.

So we find in a less striking series of instances amongst
animals that here and there the nutritional arrangements
which we have no hesitation in affirming to be the leading
characteristic of animals, and to have directly and perhaps
solely determined the great structural features of the
animal line of descent, are largely modified or even alto-
gether revolutionized. The green Hydra, the freshwater
Sponge, and some Planarian worms produce chlorophyll
corpuscles in the protoplasm of their tissues just as green
plants do, and are able in consequence to do what animals
usually cannot do namely, feed upon carbonic acid. The
possibilities of the protoplasm of the plant and of the
animal are, we are thus reminded, the same. The fact
that characteristically and typically plant protoplasm ex-
hibits one mode of activity and animal protoplasm another
does not prevent the protoplasm of even a highly developed
plant from asserting itself in the animal direction, or of a
thoroughly characterized animal, such as the green Hydra,
from putting forth its chlorophylligenous powers as though
it belonged to a plant.

Hence it is not surprising that we find among the
Protozoa, notwithstanding that they are characterized by
the animal method of nutrition and their forms determined
by the exigencies of that method, occasional instances of
partial vegetable nutrition such as is implied by the deve-
lopment of chlorophyll in the protoplasm of a few members
of the group. It would not be inconsistent with what is
observed in other groups should we find that there are
some unicellular organisms which must, on account of
their structural resemblances to other organisms, be con-
sidered as Protozoa and yet have absolutely given up alto-
gether the animal mode of nutrition (by the ingestion of
solid albumens) and have acquired the vegetable mode of
absorbing ammonia, nitrates, and carbonic acid. Experi-
ment in this matter is extremely difficult, but such " veget-
able" or "holophytic nutrition " appears to obtain in the
case of many of the green Flagellata, of the Dinoflagellata,
and possibly of other Protozoa.

On the other hand there is no doubt that we may fall
into an error in including in the animal line of descent all
unicellular organisms which nourish themselves by the
inception of solid nutriment. It is conceivable that some
of these are exceptional creophagous Protophytes parallel
at a lower level of structure to the insectivorous Phanero-
gams. In all cases we have to balance the whole of the
evidence and to consider probabilities as indicated by a
widely-reaching consideration of numerous facts.

The mere automatic motility of unicellular organisms
was at one time considered sufficient indication that such
organisms were animals rather than plants. We now know
that not only are the male reproductive cells of ferns and
similar plants propelled by vibratile protoplasm, but such
locomotive particles are recognized as common products
(" swarm-spores " and " zoospores ") of the lowest plants.

The danger of dogmatizing erroneously in distinguish-

PROTOZOA

ing Protozoa from Protophyta, and the insuperable diffi-
culty in really accomplishing the feat satisfactorily, has led
at various times to the suggestion that the effort should be
abandoned and a group constituted confessedly containing
both unicellular plants and unicellular animals and those
organisms which may be one or the other. Hacckel has
proposed to call this group the Protista (I). 1 On the
whole, it is more satisfactory to make the attempt to dis-
criminate those unicellular forms which belong to the
animal line of descent from those belonging to the veget-
able line. It is, after all, not a matter of much conse-
quence if the botanist should mistakenly claim a few
Protozoa as plants and the zoologist a few Protophyta
as animals. The evil which we have to avoid is that some
small group of unattractive character should be rejected
both by botanist and zoologist and thus our knowledge of
it should unduly lag. Bearing this in mind the zoologist
should accord recognition as Protozoa to as wide a range
of unicellular organisms as he can without doing violence
to his conception., of probability.

A very interesting and very difficult subject of speculation forces
itself on our attention when we attempt to draw the line between
the lowest plants and the lowest animals, and even comes again
before us when we pass in review the different forms of Protozoa.

That subject is the nature of the first protoplasm which was
evolved from not-living matter on the earth's surface. Was that
first protoplasm more like animal or more like vegetable proto-
plasm as we know it to-day ? By what steps was it brought into
existence ?

Briefly stated the present writer's view is that the earliest proto-
plasm did not possess chlorophyll and therefore did not possess the
power of feeding on carbonic acid. A conceivable state of things
is that a vast amount of albuminoids and other such compounds
had been brought into existence by those processes which cul-
minated in the development of the first protoplasm, and it seems
therefore likely enough that the first protoplasm fl upon these
antecedent steps in its own evolution just as animals feed on
organic compounds at the present day, more especially as the
large creeping plasmodia of some Mycetozoa feed on vegetable
refuse. It indeed seems not at all improbable that, apart from their
elaborate fructification, the Mycetozoa represent more closely than
any other living forms the original ancestors of the whole organic
world. At subsequent stages in the history of this archaic living
matter chlorophyll was evolved and the power of taking carbon
from carbonic acid. The "green" plants were rendered possible
by the evolution of chlorophyll, but through what ancestral forms
they took origin or whether more than once, i.e., by more than
one branch, it is difficult even to guess. The green Flagellate Pro-
tozoa (Volvocineaj) certainly furnish a connecting point by which
it is possible to link on the pedigree of green plants to the primi-
tive protoplasm ; it is noteworthy that they cannot be considered
as very primitive and are indeed highly specialized forms as com-
pared with the naked protoplasm of the Mycetozoou's plasmodium.

Thus then we are led to entertain the paradox that though the
animal is dependent on the plant for its food yet the animal
preceded the plant in evolution, and we look among the lower
Protozoa and not among the lower Protophyta for the nearest
representatives of that first protoplasm which was the result of a
long and gradual evolution of chemical structure and the starting
point of the development of organic form.

The Protozoan Cell-Individual compared with the Typical
Cell of Animal and Vegetable Tissues.

MORPHOLOGY.

The Protozoon individual is a single corpuscle of proto-
plasm, varying in size when adult from less than the
TU 1 uj J th of an inch in diameter (some Sporozoa and Flagel-
lata) up to a diameter of an inch (Nummulites), and even
much larger size in the plasmodia of Mycetozoa. The sub-
stance of the Protozoa exhibits the same general properties
irritability, movement, assimilation, growth, and division
and the same irremediable chemical alteration as the result
of exposure to a moderate heat, which are observed in
the protoplasm constituting the corpuscles known as cells
which build up the tissues of the larger animals and

1 These numbers refer to the bibliography at p. 866.

plants. There is therefore no longer any occasion to make
use of the word " sarcode " which before this identity was
established was very usefully applied by Dujardin (2) to
the substance which mainly forms the bodies of the
Protozoa. Like the protoplasm which constitutes the
" cells " of the Enterozoa and of the higher plants, that
of the Protozoon body is capable of producing, by chemical
processes which take place in its substance (over and above
those related merely to its nutrition), a variety of distinct
chemical compounds, which may form a deposit in or
beyond the superficial protoplasm of the corpuscle or may
accumulate centrally. These products are therefore either
ectoplastic or entoplastic. The chemical capacities of
protoplasm thus exhibited are very diverse, ranging from
the production of a denser variety of protoplasm, probably
as the result of dehydration, such as we see in the nucleus
and in the cortical substance of many cells, to the chemical
separation and deposition of membranes of pure chitin or
of cellulose or of shells of pure calcium carbonate or quasi-
crystalline needles of silica.

NUCLEUS. The nucleus is probably universally present in
the Protozoon cell, although it may have a very simple struc-
ture and be of very small size in some cases. The presence
of a nucleus has recently been demonstrated by means of
appropriate staining reagents in some Protozoa (shell-
bearing Reticularia or Foraminifera and many Mycetozoa)
where it had been supposed to be wanting, but we are not
yet justified in concluding absolutely that there are not
some few Protozoa in which this central differentiation of
the protoplasm does not exist ; it is also a fact that in the
young forms of some Protozoa which result from the
breaking up of the body of the parent into many small
" spores " there is often no nucleus present.

In contrast to this it is the fact that the cells which
build up the tissues of the Enterozoa are all derived from
the division of a nucleated egg-cell and the repeated
division of its nucleated products, and are invariably
nucleated. The same is true of tissue-forming plants,
though there are a few of the lowest plants, such as the
Bacteria, the protoplasm of which presents no nucleus. In
spite of recent statements (3) it cannot be asserted that
the cells or protoplasmic corpuscles of the yeast-plant
(Saccharomyces) and of the hyphs of many simple moulds
contain a true nucleus. We are here brought to the
question " What is a true nucleus 1 " The nucleus which
is handed on from the egg-cell of higher plants and
Enterozoa to the cells derived from it by fission has lately
been shown to possess in a wide variety of instances such
very striking characteristics that we may well question
whether every more or less distinctly outlined mass or
spherule of protoplasm which can be brought into view by
colouring or other reagents, within the protoplasmic body
of a Protozoon or a Protophyte, is necessarily to be con-
sidered as quite the same thing as the nucleus of tissue-
forming egg-cell-derived cells.

Kesearches, chiefly due to Flemming (4), have shown
that the nucleus in very many tissues of higher plants
and animals consists of a capsule containing a plasma of
" achromatin " not deeply stained by reagents, ramifying
in which is a reticulum of "chromatin" consisting of fibres
which readily take a deep stain (Fig. I., A). Further it is
demonstrated that, when the cell is about to divide into
two, definite and very remarkable movements take place
in the nucleus, resulting in the disappearance of the
capsule and in an arrangement of its fibres first in the
form of a wreath (Fig. I., D) and subsequently (by the
breaking of the loops formed by the fibres) in the form of a
star (E). A further movement within the nucleus leads to
an arrangement of the broken loops in two groups (F), the
position of the open ends of the broken loops being reversed

PROTOZOA

as compared with what previously obtained. Now the
two groups diverge, and in many cases a striated appear-
ance of the achromatin substance between the two groups
of loops of chromatin is observable (H). In some cases
(especially egg-cells) this striated arrangement of the
achromatin substance precedes the separation of the loops
(G). The striated achromatin is then termed a " nucleus-
spindle," and the group of chromatin loops (Fig. I., G, a)

FIG. I. Karyokinesis of a typical tissue-cell (epithelium of Salamander) alter
Flemming and Klein. The series from A to I represent the successive stag es
in the movement of the chromatin fibres during division, excepting G. which
represents the " nucleus-spindle "of an egg-cell. A, resting nucleus; D, wreath-
form; E, single star, the loops of the wreath being broken; F, separation of the
star into two groups of U-shaped fibres; H", diaster or double star; I, comple-
tion of the cell-division and formation of two resting nuclei. In G the
chromatin fibres are marked a, and correspond to the phase shown in F ; they
are in this case called the "equatorial plate"; b, achromatin fibres forming the
nucleus-spindle; c, granules of the cell-protoplasm forming a "polar star."
Such a polar star is seen at each end of the nucleus-spindle, and is not to be
confused with the diaster H.

is known as "the equatorial plate." At each end of
the nucleus-spindle in these cases there is often seen a
star consisting of granules belonging to the general proto-
plasm of the cell (G, c). These are known as " polar stars."
After the separation of the two sets of loops (H) the
protoplasm of the general substance of the cell becomes
constricted, and division occurs, so as to include a group of
chromatin loops in each of the two fission products. Each
of these then rearranges itself together with the associated
achromatin into a nucleus such as was present in the
mother-cell to commence with. This phenomenon is termed
" karyokinesis," and has been observed, as stated above,
in a large variety of cells constituting tissues in the higher
animals and plants.

There is a tendency among histologists to assume that
this process is carried out in all its details in the division
of all cells in the higher plants and animals, and accordingly
to assume that the structural differentiation of achromatin
plasma and chromatin nucleus-fibres exists in the normal
nucleus of every such cell. If this be true, it is necessary
to note very distinctly that the nucleus of the Protozoon
cell-individual by no means conforms universally to this
model. As will be seen in the sequel, we find cases in
which a close approach is made by the nucleus of Protozoa
to this structure and to this definite series of movements
during division (Fig. VIII. 3 to 12, and Fig. XXV.); and
a knowledge of these phenomena has thrown light upon
some appearances (conjugation of the Ciliata) which were
previously misinterpreted. But there are Protozoa with a
deeply-placed nucleus-like structure which does not pre-
sent the typical structure above described nor the typical
changes during division, but in which on the contrary the
nucleus is a very simple homogeneous corpuscle or vesicle
of more readily stainable protoplasm.

The difficulties of observation in this matter are great,
and it is proportionately rash to generalize ; but it appears
that we are justified at the present moment in asserting
that not all the cells even of higher plants and animals

exhibit in full detail the structure and movement of the
typical cell-nucleus above figured and described; and accord-
ingly the fact that such structure and movement cannot
always be detected in the Protozoon cell-nucleus must not
be regarded as either an isolated phenomenon peculiar to
such Protozoon cells, nor must it be concluded that we have
only to improve our means of analysis and observation in
order to detect this particular structure in all nuclei. It
seems quite possible and even probable that nuclei may
vary in these details and yet be true nuclei. Some nuclei
which are observed in Protozoon cell-bodies may be regarded
as being at a lower stage of differentiation and specializa-
tion than are those of the epithelial and embryonic cells
of higher animals which exhibit typical karyokinesis.
Others on the contrary, such as the nuclei of some
liadiolaria (ride infra), are probably to be regarded as
more highly developed than any tissue cell-nuclei, and will
be found by further study to present special phenomena
peculiar to themselves. In some of the highest Protozoa
(the Ciliata) it has lately been shown that the nucleus
may have no existence as such, but is actually dispersed
throughout the protoplasm in the form of fine particles of
chromatin-substance which stain on treatment with car-
mine but are in life invisible (84). This diffuse condition
of the nuclear matter has no parallel, at present known, in
tissue-cells, and curiously enough occurs in certain genera
of Ciliata whilst in others closely allied to them a solid
single nucleus is found. The new results of histological
research have necessitated a careful study of the nucleus
in its various stages of growth and division in the cell-
bodies of Protozoa and a comparison of the features there
observed with those established as " typical " in tissue-cells.
Accordingly we have placed the figure and explanation of
the typical cell-nucleus in the first place in this article for
subsequent reference and comparison.

CORTICAL SUBSTANCE. The superficial protoplasm of
an embryonic cell of an Enterozoon in the course of its
development into a muscular cell undergoes a change
which is paralleled in many Protozoa. The cortical layer
becomes dense and highly refringent as compared with the
more liquid and granular medullary substance. Probably
this is essentially a change in the degree of hydration of
the protoplasm itself, although it may be accompanied by
the deposition of metamorphic products of the protoplasm
which are not chemically to be regarded as protoplasm.
The differentiation of this cortical substance (which is not
a frequent or striking phenomenon in tissue-cells) may be
regarded as an ectoplastic (i.e., peripheral) modification
of the protoplasm, comparable to the entoplastic (central)
modification which produces a nucleus.

The formation of " cortical substance " in the Protozoa
furnishes the basis for the most important division into
lower and higher forms, in this assemblage of simplest
animals. A large number (the Gymnomyxa) form no
cortical substance ; their protoplasm is practically (except-
ing the nucleus) of the same character throughout. A
nearly equally large number (the Corticata) develop a
complete cortical layer of denser protoplasm, which is
distinct from the deeper medullary protoplasm. This
layer is permanent, and gives to the body a definite shape
and entails physiological consequences of great moment.
The cortical protoplasm may exhibit further specialization of
structure in connexion with contractile functions (muscular).

ECTOPLASTIC PRODUCTS CHEMICALLY DISTINCT FROM
PROTOPLASM. The protoplasm of all cells may throw down
as a molecular precipitate distinct from itself chemical
compounds, such as chitin and horny matter and other
nitrogenized bodies, or again non-nitrogenous compounds,
such as cellulose. Very usually these substances are
deposited not external to but in the superficial proto-

PROTOZOA

plasm. They are then spoken of as cell-cuticle if the cell
bounds the free surface of a tissue, or as matrix or cell-wall
in other cases. The Protozoon cell-body frequently forms
such "cuticles," sometimes of the most delicate and
evanescent character (as in some Amcebse), at other times
thicker and more permanent. They may give indications
(though proper chemical examination is difficult) of being
allied in composition to chitin or gelatin, in other instances
to cellulose, which is rare in animals and usual in plants.
These cuticular deposits may be absent, or may form thin
envelopes or in other cases jelly-like substance intimately
mixed with the protoplasm (Radiolaria). They may take
the form of hooks, tubercles, or long spines, in their
older and more peripheral parts free from permeation by
protoplasm, though deeply formed in and interpenetrated
by it. Such pellicles and cuticles, the deeper layers (if not
the whole) of which are permeated by protoplasm, lead
insensibly to another category of ectoplastic products in
which the material produced by the protoplasm is separated
from it and can be detached from or deserted by the proto-
plasm without any rupture of the latter. These are

Shells and Cysts. Such separable investments are
formed by the cell-bodies of many Protozoa, a phenomenon
not exhibited by tissue-cells. Even the cell-walls of the
protoplasmic corpuscles of plant tissues are permeated by
that protoplasm, and could not be stripped off without
rupture of the protoplasm. The shell and the cyst of the
Protozoon are, on the contrary, quite free from the cell-
protoplasm. The shell may be of soft chitin-like sub-
stance (Gromia, &c.), of cellulose (Labyrintlmla, Dino-
flagellata), of calcium carbonate (Globigerina, etc.), or of
silica (Clathrulina, Codonella). The term "cyst" is ap-
plied to completely closed investments (" shells " having
one or more apertures), which are temporarily produced
either as a protection against adverse external conditions
or during the breaking up of the parent-cell into spores.
Such cysts are usually horny.

Stalks. By a localization of the products of ectoplastic
activity the Protozoon cell can produce a fibre or stalk of
ever-increasing length, comparable to the seta of a
Chsetopod worm produced on the surface of a single cell.

ENTOPLASTIC PRODUCTS DISTINCT FROM PROTOPLASM.
Without pausing here to discuss the nature of the finest
granules which are embedded as a dust-cloud in the hyaline
matrix of the purest protoplasm alike of Protozoa and of
the cells of higher animals and plants, and leaving aside
the discussion of the generalization that all protoplasm
presents a reticular structure, denser trabeculte of extreme
minuteness traversing more liquid material, it is intended
here merely to point to some of the coarser features of
structure and chemical differentiation, characteristic of the
cell-body of Protozoa.

With regard to the ultimate reticular structure of
protoplasm it will suffice to state that such structure has
been shown to obtain in not a few instances (e.g., Lith-
amceba, Fig. V.), whilst in most Protozoa the methods of
microscopy at present applied have not yielded evidence
of it, although it is not improbable that a recticular
differentiation of the general protoplasm similar to that of
the nucleus may be found to exist in all cells.

Most vegetable cells and many cells of animal tissues
exhibit vacuolation of the protoplasm ; i.e., large spaces are
present in the protoplasm occupied by a liquid which is not
protoplasm and is little more than water with diffusible
salts in solution. Such vacuoles are common in Protozoa.
They are either permanent, gastric, or contractile.

Permanent vacuoles containing a watery fluid are some-
times so abundant as to give the protoplasm a "bubbly"
structure (Thalamophora, Radiolaria, etc.), or may merely
give to it a trabecular character (Trachelius, Fig. XXIV.

14, and Noctiluca, Fig. XXVI. 18). Such vacuoles may
contain other matters than water, namely, special chemical
secretions of the protoplasm. Of this nature are oil-drops,
and from these we are led to those deposits within the
cell-protoplasm which are of solid consistence (see below).

Gastric vacuoles occur in the protoplasm of most Proto-
zoa in consequence of the taking in of a certain quantity
of water with each solid particle of food, such ingestion of
solid food-particles being a characteristic process bound up
with their animal nature.

Contractile vacuoles are frequently but not universally
observed in the protoplasm of Protozoa. They are not
observed in the protoplasm of tissue-cells. The contrac-
tile vacuole whilst under observation may be seen to
burst, breaking the surface of the Protozoon and discharg-
ing its liquid contents to the exterior ; its walls, formed of
undifferentiated protoplasm, then collapse and fuse. After
a short interval it re-forms by slow accumulation of liquid
at the same or a neighbouring spot in the protoplasm.
The liquid is separated at this point by an active process
taking place in the protoplasm which probably is of an
excretory nature, the separated water carrying with it
nitrogenous waste-products. A similar active formation
of vacuoles containing fluid is observed in a few instances
(Arcella, some Amosbas) where the protoplasm separates a
gas instead of liquid, and the gas vacuole so produced ap-
pears to serve a hydrostatic function.

Corpuscular and Amorphous Entoplastic Solids. Con-
cretions of undetermined nature are occasionally formed
within the protoplasm of Protozoon cells, as are starch and
nitrogenized concretions in tissue-cells (Lithamceba, Fig.
V. cone.). But the most important corpuscular products
after the nucleus, which we have already discussed, are
chlorophyll corpuscles. These are (as in plants) concavo-
convex or spherical corpuscles of dense protoplasm resem-
bling that of the nucleus, which are impregnated superfi-
cially with the green-coloured substance known as chloro-
phyll. They multiply by fission, usually tetraschistic,
independently of the general protoplasm. They occur in
representatives of many different groups of Protozoa (Pro-
teomyxa, Heliozoa, Labyrinthulidea, Flagellata, Ciliata),
but are confined to a few species. Similar corpuscles or
band-like structures coloured by other pigments are occa-
sionally met with (Dinoflagellata).

Recently it has been maintained (Brandt, 5) that the
chlorophyll corpuscles of Protozoa and other animals are
parasitic Algae. But, though it is true that parasitic Algre
occur in animal tissues, and that probably this is the nature
of the yellow cells of Radiolaria, yet there seems to be no
more justification for regarding the chlorophyll corpuscles
of animal tissue-cells and of Protozoa as parasites than
there is for so regarding the chlorophyll corpuscles of the
leaves of an ordinary green plant.

Corpuscles of starch, paramylum, and other amyloid
substances are commonly formed in the Flagellata, whose
nutrition is to a large extent plant-like.

Entoplastic Fibres. A fibrillation of the protoplasm of
the Protozoon cell-body may be produced by differentia-
tion of less and more dense tracts of the protoplasm itself.
But as distinct from this we find horny fibres occasionally
produced within the protoplasm (Heliozoa) having definite
skeletal functions. The threads produced in little cavities
in the superficial protoplasm of many Ciliate Protozoa,
known as trichocysts, may be mentioned here.

Entoplastic Spicules. m Needle-like bodies consisting
either of silica or of a horny substance (acanthin) are
produced in the protoplasm of many Protozoa (Heliozoa,
Radiolaria). These are known as spicules ; they may be
free or held together in groups and arranged either radially
or tangentially in reference to the more or less spherical

6

PROTOZOA

body of the Protozoon. A similar production of siliceous
spicules is observed in the tissue-cells of Sponges. Crys-
tals of various chemical nature (silica, calcium carbonate,
oxalate, <fcc.) are also frequently deposited in the protoplasm
of the Protozoa, differing essentially from spicules in that
their shape is due purely to crystallization.

GENERAL FORM OF THE PROTOZOON CELL. Those Proto-
zoa which have not a differentiated cortical substance, and
are known as Gymnomyxa, present very generally an
extreme irregularity of contour. Their protoplasm, being
liquid rather than viscous, flows into the most irregular
shapes. Their fundamental form when at rest is in many
cases that of the sphere ; others are discoidal or may be
monaxial, that is to say, show a differentiation of one
region or " end " of the body from the other. Frequently
the protoplasm is drawn out into long threads or filaments
which radiate uniformly from all parts of the spherical or
discoidal cell-body or originate from one region to the
exclusion of other parts of the surface.

These non-corticate Protozoa can take solid particles of
food into their protoplasm, there to be digested in an
extemporized "gastric vacuole," at any part or most parts
of their superficies. They have no permanent cell-mouth
leading into the soft protoplasm since that soft protoplasm
is everywhere freely exposed.

The corticate Protozoa have (with the exception of some
parasites) one, and in the Acinetaria more than one, de-
finite aperture in the cortical substance leading into the
softer medullary protoplasm. This is the cell-mouth,
morphologically as distinct from the mouth of an Entero-
zoon as is the hole in a drain pipe from the front door of
a house, but physiologically subserving the same distinc-
tively animal function as does the mouth of multicellular
animals. The general form of the body is in these Proto-
zoa oblong, with either monaxial symmetry, when the
mouth is terminal, or bilateral symmetry, when the body
is oblong and flattened and the mouth is towards one end
of what becomes by its presence the " ventral " surface.
Though the protoplasm is not nakedly exposed in irregular
lobes and long filaments in these corticate Protozoa so as
to pick up at all points such food-particles as may fall in
its way, yet the protoplasm does in most Corticata project
in one or more peculiarly modified fine hair-like processes
from the otherwise smooth surface of the cell-body.
These processes are vibratile. cilia, identical in character
with the vibratile cilia of epithelial tissue-cells of Entero-
zoa. They are essentially locomotor and current-produc-
ing (therefore prehensile) organs, and, whilst unable to
ingest solid food-particles themselves, serve to propel the
organism in search of food and to bring food into the cell-
mouth by the currents which they excite. Either a single
vibratile filament is present, when it is called a flagellum,
or a row or many rows of cilia are developed.

Constituent cells of the Enterozoa are well known which
closely resemble some of the Gymnomyxa or non-corticate
Protozoa in their general form. These are the colourless
blood corpuscles or lymph corpuscles or phagocytes (Mecz-
nikow, 6) which float freely in the blood and ingest solid
particles at any part of their surface as do non-corticated
Protozoa ; they exhibit a similar irregularity and muta-
bility of outline, and actually digest the particles which
they take in. The endodermal digestive cells of some
Enterozoa (Coslentera and Planarians) are also naked proto-
plasmic corpuscles and can take in solid food-particles.

No tissue-cells are known which present any close
parallel to the mouth-bearing corticate Protozoa. The
differentiation of the structure of a single cell has in these
forms reached a very high degree, which it is not surpris-
ing to find without parallel among the units which build
up the individual of a higher order known as an Entfiro-

zoon. Cilia are developed on such cell-units (ciliated
epithelium), but not used for the introduction of food-
particles into the cell. In rare cases (the ciliated " pots "
of the vascular fluid of Sipunculus) they act so as to freely
propel the ciliated cell through the liquid " blood " of the
Enterozoon, as the cilia of a Protozoon propel it through
water. An aperture in the cortical substance (or in
the cuticular product) of a tissue-cell is sometimes to be
observed, but is never (?) used for the ingestion of food-
particles. Such an aperture occurs in unicellular glands,
where it serves as the outlet of the secretion.

PHYSIOLOGY.

Hution. As has just been hinted, the movement of
protoplasm, which in the tissue -cells of Enterozoa and
higher plants is combined and directed so as to produce
effects in relation to the whole organism built up of
countless cells, is seen in the Protozoa in a different
relation, namely, as subserving the needs of the individual
cell of which the moving protoplasm is the main sub-
stance. The phenomena known in tissue-cells as " stream-
ing" (e.g., in the cells of the hairs of Tradescantia),
as local contraction and change of form (e.g., in the
corpuscles of the cornea), as muscular contraction, and as
ciliary movement are all exhibited by the protoplasm of
the cell-body of Protozoa, with more or less constancy,
and are intimately related to the processes of hunting,
seizing, and ingesting food, and of the intercourse of the
individuals of a species with one another and their evasion
of hostile agencies. Granule streaming and the implied
movement of currents in the protoplasm are seen in the
filamentous protoplasm of the Heliozoa, Radiolaria, Reti-
cularia, and Noctiluca, and in the cyclosis of the gastric
vacuoles of Ciliata. Local contraction and change of form
is seen best in the Amcebze and some Flagellata, where it
results in locomotion. Definite muscular contraction is
exhibited by the protoplasmic band in the stalk of Vorti-
cella, by the leg-like processes of the Hypotrichous Ciliata,
and by the cortical substance of some large Ciliata. Cili-
ary movement ranging from the vibration of filaments of
protoplasm temporarily evolved, up to the rhythmic beat
of groups of specialized cilia, is observed in all groups of
Protozoa in the young condition if not in the adult, and
special varieties of ciliary movement and of cilia-like
organs will be noted below. For an account of the con-
ditions and character of protoplasmic movement generally
which cannot be discussed in the present article the reader
is referred to Engelmann (7).

The protoplasm of the cell-body of the Protozoa is drawn
out into lobes and threads which are motile and are used
as locomotive and prehensile organs. These processes are
of two kinds, which are not present on the same cell and
are not capable of transmutation, though there are excep-
tions to both of these statements. The one kind are
termed " pseudopodia," and are either lobose or filamentous
or branched and even reticular (Figs. IV.and IX.). The Pro-
tozoa which exhibit them are sometimes termed Myxopods.
The other kind are cilia and flagella, and are simple threads
which are alternately bent and straightened almost inces-
santly during the life of the organism. These Protozoa
are termed Mastigopods. Whilst the cilia and flagella are
permanent organs, the pseudopodia vary greatly in char-
acter ; they are in some cases rapidly expanded and with-
drawn in irregular form, and can hardly be said to be more
than lobose protuberances of the flowing moving mass of
protoplasm. In other cases they are comparatively per-
manent stiff threads of protoplasm which can be contracted
and can fuse with one another but rarely do so (Heliozoa,
Eadiolaria). Between these extreme forms of "pseudo-
podia " there are numerous intermediate varieties, and the

PROTOZOA

whole protoplasmic body of the Protozoon may even
assume the form of a slowly changing network of threads
of greater or less tenuity (Chlamydomyxa, Fig. VI.).

Nutrition. Typically that is to say, by determinate
hereditary tendency the Protozoa take solid food-particles
into their protoplasm which form and occupy with the water
surrounding them " gastric vacuoles " in the protoplasm.
The food-particle is digested in this vacuole, by what
chemical processes is not ascertained. It has been shown
that the contents of the gastric vacuole give in some cases
an acid reaction, and it is not improbable that free acid is
secreted by the surrounding protoplasm. It is not known
whether any ferment 1 is separated by the protoplasm,
but it is probable frcm observations made on the digestive
process of Ccclentera (Actinia) that the ferment is not
separated, but that actual contact of the food-particle with
the protoplasm is necessary for a " ferment influence " to be
exerted. The digestion of a food-particle by a Protozoon
is intra-cellular, and has been contrasted with the cavitary
digestion of higher animals. In the latter, ferments and
acids are poured out by the cells bounding the enteric
cavity into that space, and digestion is extra-cellular. In
the lowest Enterozoa (many Ccelentera and some Planarian
worms) it has been shown that food-particles are actually
taken up in a solid state by the soft protoplasm of the
enteric cells and thus subjected to intra-cellular digestion.
There appears to be a gradual transition from this process,
in which close contact with living protoplasm is necessary
that the solution of an albuminous food-particle may be
effected, onwards to the perfectly free cavitary digestion
by means of secretions accumulated in the enteron.

We have not yet any satisfactory observations on the
chemistry of intra-cellular digestion either of Protozoa or
of Ccelentera.

Certain Protozoa which are parasitic do not take solid
food particles ; they (like higher parasites, such as the
Tapeworms) live in the nutritious juices of other animals
and absorb these by their general surface in a liquid state.
The Gregarinse (Sporozoa), many Ciliata, &c., are in this
case. Other Protozoa are known which are provided with
chlorophyll corpuscles and do not take in solid food, but,
apparently as a result of exceptional adaptation in which
they differ from closely-allied forms, nourish themselves
as do green plants. Such are the Volvocinean Flagellata
and some of the Dinoflagellata. It has also been asserted
that other Protozoa (viz., some Ciliata) even some which
possess a well-developed mouth can (and experimentally
have been made to) nourish themselves on nitrogenous
compounds of a lower grade than albumens such, for
instance, as ammonium tartrate. Any such assertions
must be viewed with the keenest scepticism, since experi-
mental demonstration of the absence of minute albuminous
particles (e.g., Bacteria) from a solution of ammonium
tartrate in which Ciliate Protozoa are flourishing is a
matter of extreme difficulty and has not yet been effected.

Undigested food-remnants are expelled by the protoplasm
of the Protozoon cell either at any point of the surface or
by the cell-mouth or by a special cell-anus (some Ciliata,
see Fig. XXIV. 22).

Respiration and Excretion. The protoplasm of the
Protozoa respires, that is, takes up oxygen and liberates
carbonic acid, and can readily be shown experimentally
to require a supply of oxygen for tlie manifestation of its
activity. No special respiratory structures are developed
in any Protozoa, and as a rule also the products of oxida-
tion appear to be washed out and removed from the proto-
plasm without the existence of any special apparatus.

1 The digestive ferment pepsin has been detected by Krukenln-vi,' in
the plasmodium of the Mycetozooa Fuligo (flowers of tan). See on
this subject Zopf (13), p. 88.

The contractile vacuole which exists in so many Protozoa
Mppoars, however, to be an excretory organ. It has been
shown to rapidly excrete in a state of solution colouring
matters (anilin blue) which have been administered with
food particles (8). No evidence has been adduced to show
whether traces of nitrogenous waste-products are present
in the water expelled by the contractile vacuole.

Chemical Metamorphosis. The form which the various
products of the activity of the Protozoon's protoplasm may
assume has been noted above. It will be sufficient here
to point out that the range of chemical capacities is quite
as great as in the cells of the higher Enterozoa. Chitin,
cellulose, silicon, calcium carbonate, fats, pigments, and
gases can be both deposited and absorbed by it. Owing
to the minuteness of the Protozoa, we are at present unable
to recognize and do justice to the variety of chemical bodies
which undoubtedly must play a part in their economy as
the result of the manufacturing activity of their pro-
toplasm. See, however, Zopf (13), p. 71.

Growth and Reproduction. The Protozoon cell follows
the same course as tissue-cells, in that by assimilation of
nutriment its protoplasm increases in volume and reaches
a certain bulk, when its cohesion fails and the viscid
droplet divides into two. The coefficient of cohesion
varies in different genera and species, but sooner or later
the disrupting forces lead to division, and thus to multi-
plication of individuals or reproduction. The phenomena
connected with the division of the nucleus (already alluded
to) will be noticed in particular cases below.

Whilst simple binary division is almost without excep-
tion a chief method of reproduction among the Protozoa,
it is also very usual, and probably this would be found if
our knowledge were complete to have few exceptions, that
under given conditions the Protozoon breaks up rapidly
into many (from ten to a hundred or more) little pieces,
each of which leads an independent life and grows to the
form and size of its parent. It will then multiply by
binary division, some of the products of which division
will in their turn divide into small fragments. The small
fragments are called " spores." Usually the Protozoon
before breaking up into spores forms a " cyst " (see above)
around itself. Frequently, but not as a necessary rule,
two (rarely three or more) Protozoon cell-individuals come
together and fuse into one mass before breaking up into
spores. This process is known as "conjugation;" and
there can be no doubt that the physiological significance
of the process is similar to that of sexual fertilization,
namely, that the new spores are not merely fragments of
an old individual but are something totally new inasmuch
as they consist of a combination of the substance of indi-
viduals who have had different life experiences.

Whilst spore-formation is not necessarily preceded by
conjugation, conjugation is not necessarily followed by
spore-formation. Among the Mycetozoa the young indi-
viduals produced from spores conjugate at a very early
period of growth in numbers and form "plasmodia," and
after a considerable interval of feeding and growth the
formation of spores takes place. Still more remarkable is
the fact observed among the Ciliata where two individuals
conjugate and after a brief fusion and mixture of their
respective protoplasm separate, neither individual (as far
as certain genera at least are concerned) breaking up into
spores, but simply resuming the process of growth and
recurrent binary division with increased vigour.

There is certainly no marked line to be drawn between
reproduction by simple fission and reproduction by spore-
formation ; both are a more or less complete dividing of
the parent protoplasm into separate masses ; whether the
products of the first fission are allowed to nourish them-
selves and grow before further fission is carried out or not

8

PROTOZOA

does not constitute an essential difference. The fission of
the Ciliate Protozoon, Opalina (see below Fig. XXIV. 4-8),
is a step from the ordinary process of delayed binary divi-
sion towards spore-formation. In some Protozoa spores are
produced after encystation by a perfectly regular process
of cleavage (comparable to the cleavage of the egg-cell
of Enterozoa) first two, then four, than eight, sixteen,
and thirty-two fission products being the result (see
Fig. XX. 24, 25, &c.).

But more usually there is a hastening of the process,
and in these cases it is by no means clear what part the
parent cell-nucleus takes. An encysted Gregarina (or two
conjugated Gregarinse) suddenly breaks up into a number
of equal-sized spores, which do not increase in number by
binary division and have not been formed by any such
process. This multicentral segregation of the parent pro-
toplasm is a marked development of the phenomenon of
sporulatiou and remote from ordinary cell-division. How
it is related to ordinary cell-division is not known, inas-
much as the changes undergone by the nucleus in this
rapid multicentral segregation of the parent protoplasm
have not been determined. The spores of Protozoa may
be naked or encased singly or in groups in little en-
velopes, usually of a firm horny substance (see Fig.
XX. 23 to 26, and Fig. XXIV. 15 to 18). Whenever
the whole or a part of a Protozoon cell divides rapidly
into a number of equal-sized pieces which are simultane-
ously set free and are destined to reproduce the adult
form, the term spore is applied to such pieces, but the
details of their formation may vary and also those of their
subsequent history. In typical cases each spore produced
as the result of the fission of an encysted Protozoon (con-
jugated or single) has its own protective envelope, as in
the Mycetozoa (Fig. III.) and the Sporozoa (Fig. XVIII.),
from which the contained protoplasm escapes by " ger-
mination " as a naked corpuscle either flagellate or amcebi-
form. In some terminologies the word " spore " is limited
to such a "coated" spore, but usually the naked proto-
plasmic particles which issue from such " coated " spores,
or are formed directly by the rapid fission of the parent
Protozoon, are also called " spores." The former condition
is distinguished as a " chlamydospore, " whilst the latter are
termed " gymnospores." Many Protozoa produce gymno-
spores directly by the breaking up of their protoplasm,
and these are either " ftagellulse " (swarm-spores) or "amce-
buke " (creeping spores). The production of coated spores
is more usual among the lower plants than it is among
Protozoa, but is nevertheless a characteristic feature of
the Gregarinse (Sporozoa) and of the Mycetozoa. The
term " gemma " or " bud-spore " is applied to cases, few
in number, where (as in Acinetaria, Fig. XXVI., Spiro-
chona, Fig. XXIII. 10, and Reticularia, Fig. X. 8) the
spores are gradually nipped off from the parent-cell one
or more at a time. This process differs from ordinary
cell-division only in the facts (1) that the products of
division are of unequal size the parent-cell being distin-
guishable as the larger and more complete in structure,
and (2) that usually the division is not binary, but more
than one bud-spore is produced at a time.

Whilst in the binary cell-division of the Protozoa the
two products are usually complete in structure at the
period of separation, spores and spore-buds are not only of
small size and therefore subject to growth before attaining
the likeness of the parent, but they are also very often of
simple and incomplete structure. The gap in this respect
between the young spore and its parent necessarily varies
according to the complexity of the parental form.

In the case of the Eadiolaria, of the Gregarinse, of
Noctiluca, and of the Acinetaria, for instance, the spore
has before it a considerable process of development in

structure and not merely of growth, before attaining the
adult characters. Hence there is a possible embryology
of the Protozoa, to the study of which the same prin-
ciples are applicable as are recognized in the study of the
embryology of Enterozoa. Embryonic forms of great sim-
plicity of structure, often devoid of nucleus, and consist-
ing of simple elongate particles of protoplasm, are hatched
from the spore-cases of the Gregarime (Fig. XVII. 13, 14).
These gradually acquire a differentiated cortical protoplasm
and a nucleus. A very large number of Gymnomyxa pro-
duce spores which are termed "monadiform," that is, have
a single or sometimes two filaments of vibratile protoplasm
extended from their otherwise structureless bodies. By
the lashing of these flagella the spores (swarm-spores or
zoospores) are propelled through the water. The resem-
blance of these monadiform young (best called " flagel-
lulce ") to the adult forms known as Flagella ta has led to
the suggestion that we have in them a case of recapitula-
tive development, and that the ancestors of the Gymno-
myxa were Protozoa similar to the Flagellata. Again the
Acinetaria produce spores which are uniformly clothed
with numerous vibratile cilia (Fig. XXVI.), although the
adults are entirely devoid of such structures ; this is
accounted for by the supposition that the Aciuetaria
have been developed from ancestors like the Ciliata, whose
characters are thus perpetuated in their embryonic stages.
There can be little doubt that these embryological sugges-
tions are on the whole justified, and that the nucleated
Protozoa are the descendants of non-nucleated forms simi-
lar to the spores of Gymnomyxa and Sporozoa, whilst it
seems also extremely probable that the ancestral Protozoa
were neither exclusively amoeboid in the movement of
their protoplasm nor provided with permanent vibratile
filaments (flagella and cilia) ; they were neither Myxopods
nor Mastigopods (to use the terms which have been intro-
duced to express this difference in the character of the
locomotor processes), but the same individuals were capable
of throwing out their protoplasm sometimes in the form
of flowing lobes and networks, sometimes in the form of
vibratile flagella. A few such undifferentiated forms exist
at the present day among the Proteomyxa and in a little
more advanced condition among the lowest Flagellata, e.g.,
Ciliophrys.

Death. It results from the constitution of the Proto-
zoon body as a single cell and its method of multiplication
by fission that death has no place as a natural recurrent
phenomenon among these organisms. Among the Entero-
zoa certain cells are separated from the rest of the consti-
tuent units of the body as egg-cells and sperm-cells ; these
conjugate and continue to live, whilst the remaining cells,
the mere carriers as it were of the immortal reproductive
cells, die and disintegrate. There being no carrying cells
which surround, feed, and nurse the reproductive cells of
Protozoa, but the reproductive cell being itself and alone
the individual Protozoon, there is nothing to die, nothing
to be cast off by the reproductive cell when entering on a
new career of fission. The bodies of the higher animals
which die may from this point of view be regarded as
something temporary and non-essential, destined merely to
carry for a time, to nurse, and to nourish the more import-
ant and deathless fission-products of the unicellular egg.
Some of these fission-products of the new individual de-
veloped from an egg-cell namely, the egg-cells and sperm-
cells are as immortal as the unicellular Protozoon. This
method of comparing the unicellular and the multicellular
organism is exceedingly suggestive, and the conception we
thus gain of the individuality of the Enterozoon throws
light upon the phenomena of reproduction and heredity in
those higher organisms.

Experiment and observation in this matter are extremely

PROTOZOA

9

difficult ; but we have no reason to suppose that there is
any inherent limit to the process of nutrition, growth, and
fission, by which continuously the Protozoa are propagated.
The act of conjugation from time to time confers upon
the protoplasm of a given line of descent new properties,
and apparently new vigour. Where it is not followed by
a breaking up of the conjugated cells into spores, but by
separation and renewed binary fission (Ciliata), the result
is described simply as " rejuvenescence." The protoplasm
originated by the successive division of substance traceable
to one parent cell has become specialized, and in fact too
closely adapted to one series of life-conditions ; a fusion
of substance with another mass of protoplasm equally
specialized, but by experience of a somewhat differing
character, imparts to the resulting mixture a new com-
bination of properties, and the conjugated individuals on
separation start once more on their deathless career with
renewed youth.

CLASSIFICATION OF THE PROTOZOA.

In attempting a scheme of classification it would be most in
accordance with the accepted probabilities of the ancestral history
of the Protozoa to separate altogether those forms devoid of a
nucleus from those which possess one, and to regard them as a
lower "grade" of evolution or differentiation of structure.

By some systematists, notably Butschli (9), the presence or
absence of a nucleus has not been admitted as a basis of elassifica-
tory distinction, whilst on the other hand both Haeckel (1) ami
Huxley (10) have insisted on its importance.

The fact is that during recent years many of those Protozoa
which were at one time supposed to be devoid of nucleus even in a
rudimentary form, and furnished therefore the tangible basis for a
lowest group of "Protozoa Homogenea" or "Monera," have been
shown by the application of improved methods of microscopic
investigation to possess a nucleus, that is to say, a differentiated
corpuscle of denser protoplasm lying within the general protoplasm,
and capable when the organism is killed by alcohol or weak acids
of taking up the colour of various dyes (such as carmine and
heematoxylin) more readily and permanently than is the general
protoplasm. In such cases the nucleus may be very small and
exhibit none of the typical structure of larger nuclei. It is usually
surrounded by a clear (i.e., non-granular) halo of the general
protoplasm which assists the observer in its detection. Nuclei
have been discovered in many Reticularia (Foraminifera), a group
in which they were supposed to be wanting, by Schultze (11) and
the Hertwigs (12) and more recently in the Mycetozoa and in
Vampyrella and Protomonas (Zopf, 13), where so excellent an
observer as C'ienkowski had missed them.

It seems therefore not improbable that a nucleus is present
though not observed in Protomyxa, Myxastrum, and other similar
forms which have been by Haeckel and others classed as " Monera "
or "Homogenea." The recently described (14) Archerina (Fig. II.
8, 11) certainly possesses no nucleus in the usual sense of that term,
but it is possible that the chlorophyll-coloured corpuscles of that
organism should be considered as actually representing the nucleus.
Whilst then refraining from asserting that there are no existing
Protozoa devoid of nucleus corresponding in this character with
non-nucleate Protophyta, such as the Bacteria, we shall not in our
scheme of classification institute a group of Homogenea, but shall
leave the taking of that step until it has been shown after critical
examination that those forms now regarded by some observers as
Homogenea are really so. In the meantime these forms will find
their places alongside of the Nueleata most nearly allied to them
in other characters.

The Protozoa with a definite permanent cortical substance of
differentiated protoplasm are undoubtedly to be regarded as evolved
from forms devoid of such differentiation of their substance, and
we accordingly take this feature as the indication of a primary
division of the Protozoa. 1 The lower grade, the Gymnomyxa,
afford in other respects evidence of their being nearly related to
the ancestral forms from which the Corticata (the higher grade)
have developed. The Gymnomyxa all or nearly all, whilst
exhibiting amoeboid movement and the flowing of their protoplasm
into " pseudopodia " of very varied shapes, produce spores which
swim by means of one or two flagella of vibratile protoplasm
(monadiform young or flagelluhe). These flagellate young forms

1 The " exoplasm " and "endoplasm" described in Amceboe, &c. ,
by some authors are not distinct layers but one and the same con-
tinuous substance what was internal at one moment becoming ex-
ternal at another, no really structural difference existing between
them.

are closely related to the Flagellata, a group of the Corticata from
which it seems probable that the Dinodagellata, the Ciliata, and
the Acinetaria have been derived. The Gymnomyxa themselves
cannot, on account of the small number of structural features
which they offer as indications of affinity and divergence in genetic
relationships inter sc, be classified with anything like confidence in
a genealogical system. We are obliged frankly to abandon the
attempt to associate some of the simpler forms with their nearest
genetic allies and to content ourselves with a more or less artificial
system, which is not, however, artificial in so far as its main
groups are concerned. Thus the genetic solidarity of each of the
large classes Heliozoa, Reticularia, Mycetozoa, and liadiolaria is
not open to question. The Lobosa on the other hand appear to
be a more artificial assemblage, and it is difficult to say that
genetically there is any wide separation between them and the
Mycetozoa or between the Mycetozoa and some of the simpler
forms which we bring together under the class Proteornyxa.
The scheme of classification which we adopt is the following :

PROTOZOA.

G r. ADE A. G YMNOM YXA.
( Class I. PROTEOMYXA.
j Ex. Vampyrella, Protomyxa, Anlierina.
Class II. MYCETOZOA.

Ex. The Eu-mycetozoa of Zopf.
Class III. LOBOSA.

Ex. Amceba, Arcclla, Pclomyxa.
r Class IV. LABYRINTHULIDBA.

Ex. Labyrinthula, Chlamydomyxa.
j Class V. HKLIOZOA.
!>! I Ex. Actinovhnis, RapJiidiophrus, Clatltrnlina.

\ Class VI. BETICULAnii.

Ex. Gromift, Lituola, Astrorhiza, Globigcrina.
\ Class VII. RADIOLARIA.
L Ex. Thalassicolla, Eucyrtidiuin, Acanthometra.

GRADE B. CORTICATA.
\ Class I. SPOROZOA.
\ Ex. Gregarina, Coccidium.
( Class II. FLAGELLATA.

Ex. Monas, Salpingceca, Eitglena, Volvox.

Class III. DlNOFLAGELLATA.

Ex. Proroccntrum, Ceratium.
Stomato- Class IV. RHYNCHOFLAGELLATA.
phora. Ex. Nodiluca.

Class V. CILIATA.

Ex. Vorticclla, Paramtzcium, Slcntor.
Class VI. ACINETARIA.

Ex. Acineta, Dendrosoma.
The genetic relationships which probably obtain among theso
groups may be indicated by the following diagram :

Sections.
Proteana.

Plasmodiata.
Lobosa.

Lipostoma.

Class Acinetaria.

Class Ciliata.

Claaa
Rhyncho-flagellata,

Class
Di no- flagella ta

Class Sporozoa.

Class
Myceujzoa.

Class \
Labyriuthulidea

(Protonucleata.J

I
Homogenea,

Literature. Certain works of an older date dealing with micro-
scopic organisms, and therefore including many Protozoa, have
historical interest. Among these we may cite 0. F. Muller,
Animalcula Infusoria, 1786; Ehrenberg, Infusionsthicrchen, 1838;

B

10

PROTOZOA

Dujardin, Histoire naturclle des Infusoires, 1841 ; Pritchard, In-
fusoria, 1857.

The general questions relating to protoplasm and to the consti-
tution of the Protozoon body as a single cell are dealt with in the
following more recent treatises : Max Schultze, Ueber dm Organ-
ismus dcr Pohjthalamicn, 1854, and Ueber das Protoplasma der
Rhizopoden wid Pflanxcnzellen, 1863; and Engelmann, article "Pro-
toplasma" in Hermann's ffandworterbuch der Physiologic, 1880.

Special works of recent date in which the whole or large groups
of Protozoa are dealt with in a systematic manner with illustra-
tions of the chief known forms are the following : Biitschli, "Pro-
tozoa," in Bronn's Classen und Ordnungen des Thierreichs, a
comprehensive and richly illustrated treatise now in course of
publication, forming the most exhaustive account of the subject
matter of the present article which has been attempted (the writer
desires to express his obligation to this work, from the plates of
which a large proportion of the woodcut figures here introduced
have been selected); W. S. Kent, Manual of the Infusoria, 1882
an exhaustive treatise including figures and descriptions of all
species of Flagellata, Dinoflagellata, Ciliata, and Acinetaria ; Stein,
Lter Organismus der Infusionsthicre, 1867-1882; Haeckel, Die
Radiolarien, 1862; Archer, "Resume of recent contributions to
our knowledge of freshwater Rhizopoda, " Quart. Jour, of Micro-
scopical Science, 1876-77; Zopf, " Pilzthiere '' (Mycetozoa), in
Encyhlopadie der Naturwissenschaftcn, Breslau, 1884.

We shall now proceed to consider the classes and orders of
Protozoa in detail.

PEOTOZOA.

Characters. Organisms consisting of a single cell or of a group
of cells not differentiated into two or more tissues ; incapable of
assimilating nitrogen in its diffusible compounds (ammonia or
nitrates) or carbon in the form of carbonates, except in special
instances which there is reason to regard as directly derived from
allied forms not possessing this capacity. The food of the Protozoa
is in consequence as a rule taken in the form of particles into the
protoplasm either by a specialized mouth or by any part of the
naked cell-substance, there to be digested and rendered diffusible.

GRADE A. GYMNOMYXA, Lankester, 1878 (64).

Characters. Protozoa in which the cell-protoplasm is entirely or
partially exposed to the surrounding medium, during the active
vegetative phase of the life-history, as a naked undifferentiated
slime or viscous fluid, which throws itself into processes or
' ' pseudopodia " of various form either rapidly changing or
relatively constant. Food can be taken into the protoplasm in the
form of solid particles at any point of its surface or at any point
of a large exposed area. The distinction into so-called "exoplasm"
and "endoplasm " recognized by some authors, is not founded on a
permanent differentiation of substance corresponding to the cortical
and medullary substance of Corticata, but is merely due to the
centripetal aggregation of granules lying in a uniform undiffer-
entiated protoplasm. The cell-individual exhibits itself under
four phases of growth and development (1) as a swarm-spore
(monadiform young or flagellula) ; (2) as an amoeba form ; (3) as
constituent of a plasmodium or cell-fusion or conjugation ; (4) as a
cyst, which may be a flagellula(Schwarme)-producing cyst, an
amcebula-producing cyst, a covered-spore(chlamydospore)-producing
cyst (sporoeyst sens, stric., Zopf), or a simple resting cyst which
does not exhibit any fission of its contents (hypnocyst). Any one
of these phases may be greatly predominant and specialized whilst
the others are relatively unimportant and rapidly passed through.

CLASS I. PROTEOMYXA, Lankester.

Characters. Gymnomyxa which exhibit in the amoeba phase
various forms of pseudopodia often changing in the same individual,
and do not produce elaborate spore cysts ; hence they are not re-
ferable to any one of the subsequent six classes. Mostly minute
forms, with small inconspicuous nucleus (absent in some?).

A division into orders and families is not desirable, the group
being confessedly an assemblage of negatively characterized or
insufficiently known forms.

Genera. Vampyrclla, Cienkowski (15); Fampyrcllulium, Zopf
(13); Spirophora, Zopf ( Amoeba radiosa, Perty) ; Haplococcus,
Zopf; Leptophrys, Hertwig and Lesser (16); Endyomena, Zopf;
BursuUa, Sorokin (17) ; Mysastrum, Haeckel (1) ; Entcromyxa,
Cienkowski (18) ; Colpudella, Cienkowski (19); Pseudospora, Cien-
kowski (20) ; Protomonas, Cienkowski (15) ; Diplophysalis, Zopf
(13); Gt/mnococcus, Zopf; Aphclidium, Zopf; Pseudosporidium,
Zopf ; Protomyxa, Haeckel (1) ; Plasmodiophora, Woronin (21) ;
Tetramyxa, Gbbel (22) ; Gloidium, Sorokin (23) ; Gymnoplirys,
Cienkowski (24) ; Myxodictyum, Haeckel (1) ; Boderia, Wright
(25) ; Biomyxa, Leidy (92) ; Protogenes, Haeckel (1) ; Protama-ba,
Haeckel (1); Nuclearia, Cienkowski (26); Monobia, Aim. Schneider
(27) ; Archerina, Lankestcr (14).

The forms here brought together include several genera (the

first nineteen) referred by Zopf to the Mycetozoa, some again
(Vampyrella, Myxastrum, Nuclearia, Monobia) which are by
Biitschli associated with the Heliozoa, others (Protamceba, Gloidium)
referred by the same authority to the Lobosa (Amcebsea) and others
(Colpodella, Protomonas) which might be grouped with the lower
Flagellata. By grouping them in the manner here adopted we
are enabled to characterize those higher groups more satisfactorily
and to give a just expression to our present want of that knowledge
of the life-history both of these forms and of the higher Gymnomyxa
which when it is obtained may enable us to disperse this hetero-
geneous class of Proteomyxa. The group lias the same function
in relation to the other classes of Gymnomyxa which the group
Vermes has been made to discharge in relation to the better denned
phyla of the Metazoa ; it is a lumber-room in which obscure, lowly-
developed, and insufficiently known forms may be kept until they
can be otherwise dealt with.

It is true that, thanks to the researches of Continental botanists
(especially Cienkowski and Zopf), we know the life-history of
several of these organisms; but we are none the less unable to con-
nect them by tangible characteristics with other Gymnomyxa.

Nearly all of the above-named genera are parasitic rather than
" voracious," that is to say, they feed on the organized products of
larger organisms both plants and animals (Haplococcus is parasitic
in the muscles of the pig), into whose tissues they penetrate, and
do not, except in a few cases (Protomyxa, Vampyrella), engulph
whole organisms, such as Diatoms, &c. , in their protoplasm. Many
live upon and among the putrefying debris of other organisms
(e.g., rotting vegetable steins and leaves, excrements of animals),
and like the Mycetozoa exert a digestive action upon the substances
with which they come in contact comparable to the putrefying and
fermentative activity of the. Schizomycetes (Bacteria).

Fig. II. illustrates four chief genera of Proteomyxa.

Protomyxa aurantiaea was described by Haeekel (1), who found
it on shells of Spirula on the coast of the Canary Islands, in the
form of orange yellow flakes consisting of branching and reticular
protoplasm nourishing itself by the ingestion of Diatoms and
Peridinia. This condition is not a simple amceba phase but a
"plasmodium" formed by the union of several young amcebte. The
plasmodium under certain conditions draws itself together into a
spherical form and secretes a clear membranous cyst around itself,
and then breaks up into some hundreds of flagellula: or swarm-
spores (Fig. IT. 2). The diameter of the cyst is '12 to '2 millimetre.
The flagellulai subsequently escape (Fig. II. 3) and swim by the
vibratile movement of one end which is drawn out in the form of a
coarse flagellum. The swarm-spore now passes into the amoeba
phase (Fig. II. 4). Several of the small amcebae creeping on the
surface of the spirula-shell then unite with one another and form
a plasmodium which continues to nourish itself by "voracious"
inception of Diatoms and other small organisms. The plasmodia
may attain a diameter of one millimetre and be visible by the
naked eye.

A nucleus was not observed by Haeckel in the spores nor in the
amceba phase, nor scattered nuclei in the plasmodium, but it is not
improbable that they exist and escaped detection in the living con-
dition, in consequence of their not being searched for by methods
of staining, &c. , which have since come into use. A contractile
vacuole does not exist.

Vampyrclla spirogyrse, Cienkowski (Fig. II. 5, 6, 7), is one of
several species assigned to the genus Vampyrella, all of which
feed upon the living cells of plants. The nucleus previously stated
to be absent has been detected by Zopf (13). There is no con-
tractile vacuole. The amceba phase has an actinophryd character
(i.e., exhibits h'ne radiating pseudopodia resembling those of the
sun-animalcule, Actinophrys, one of the Heliozoa). This species
feeds exclusively upon the contents of the cells of Spirogyra, effect-
ing an entrance through the cell-wall (Fig. II. 5), sucking out the
contents, and then creeping on to the next cell. In some species
of Vampyrella as many as four amoeba-individuals have been
observed to fuse to form a small plasmodium. Cysts are formed
which enclose in this species a single amoeba-individual. The cyst
often acquires a second or third inner cyst membrane by the
shrinking of the protoplasmic body after the first encystment and
the subsequent formation of a new membrane. The encysted pro-
toplasm sometimes merely divides into four parts each of which
creeps out of the cyst as an Actinophrys-like amoeba (Fig. II. 7) ; in
other instances it forms a dense spore, the product of which is not
known.

Protogenes primordial is is the name given by Haeckel to a
very simple form with radiating filamentous pseudopodia which
he observed in sea-water. It appears to be the same organism as
that described and figured by Max Schultze as Amceba porrccta.
Schultze's figure is copied in Fig. II. 12. No nucleus and no con-
tractile vacuole is observed in this form. It feeds voraciously on
smaller organisms. Its life-history has not been followed over even
a few steps. Hence we must for the present doubt altogether as to
its true affinities. Possibly it is only a detached portion of the
protoplasm of a larger nucleate Gymnomyxon. The same kind of

PROTOZOA

11

doubt is justified in regard to Haeckcl's Fi-ii/niim-lit. /n-imitiva, which
was uhservi'd liy liim in pond water and ilill'ers from Protogenes in
having lobose pseudopodia, wliilst agreeing with it in absence of
nuclei, contractile vacuoles, and other differentiation of structure.

FIB. II. Various Proteomyxa. 1. Protnmyxa aurantiaca, HaecM, plas-
modium phase. The naked protoplasm shows blanched, reticulate processes
(pseudopodia), and numerous non-contractile vacuoles. It is in the act of en-
pulphing a Ctratium. Shells of engulphed Ciliatu (Tintinnabula) arc embedded
deeply in the protoplasm a. 2. Cyst phase of 1'rotomyxa. a, transparent cyst-
wall ; 6, protoplasm brok'-n up into spores. 3. Flagellula phase of Protomyxa,
the form assumed by the spores on their escape from the cyst. 4. Anicebula
phase of the same, tile form assumed after a short period by the flagellula?. 5.
Vampyrella spirogyrx, Cienk., amoeba phase penetrating a cell of Spirogyra 6,
by a process of its protoplasm c, and taking up the substance of the Spirbgyra
cell, some of which is seen within the Vampyiella a. C. Large individual of
Vampyrella, showing pseudopodia p, and food particles a. The nucleus (though
present) Is not shown in this rtiawing. 7. Cyst phase of Vampyrella. The
contents of the cyst have divided into four equal parts, of which three are
visible. One is commencing to break its way through the cyst-wall /; a, food
particles. 8. Archerina Boltoni, Lankester, showing lobose and filamentous
protoplasm, and three groups of chlorophyll corpuscles. The protoplasm g is
engulphing a Bacterium i. 9. Cyst phase of Archerina. a, spinous cyst-wall ;
6, green-coloured contents. 10. Chlorophyll corpuscle of Archerina showing
tetraschistic division. 11. Actinophryd form of Archerina. b, chlorophyll cor-
puscles. 12. Proloyenes primordial^, Haeckel (Amteba porrecCa, M. Schultze),
from Schultze's figure.

The structureless protoplasmic network described by Haeckel

from spirit-preserved specimens of Atlantic ooze and identified by
him with Huxley's (28) Bathybiux, ;is also the similar network
described by Besscls (29) as Protobathybillfl, must be regarded for
tlie present as insufficiently known.

It is possible that these appearances observed in the ooze dredged
from great depths in the Atlantic are really due to simple Protozoa.
On the other hand it lias been asserted by Sir Wyville Thomson,
who at one time believed in the independent organic nature of
Bathybius, that the substance taken for protoplasm by both Huxley
and Haeckel is in reality a gelatinous precipitate of calcium
sulphate thrown down by the action of alcohol upon sea-water.
Other naturalists have pointed to the possibility of the protoplasmic
network which Bessels studied in the living condition on board
ship being detached portions of the protoplasm of Keticularia and
Radiolaria. The matter is one which requires further investigation.

Archerina Boltoni is the name given by Lankester (14) to a very
simple Gymnomyxon inhabiting freshwater ponds in company
with Desmids and other simple green Alga; (Fig. II. 8 to 11).
Archerina exhibits an amoeba phase in which the protoplasm is
thrown into long stiff filaments (Fig. II. 11), surrounding a spherical
central mass about inrVcth inch in diameter (actinophryd form).
A large vacuole (non-contractile) is present, or two or three small
ones. No nucleus can be detected by careful use of reagents in
this or other phases. The protoplasm has been seen to ingest solid
food particles (Bacteria) and to assume a lobose form. The most
striking characteristic of Archerina is the possession of chlorophyll
corpuscles. In the actinophryd form two oval green-coloured
bodies (b, 6) are seen. As the protoplasm increases by nutrition the
chlorophyll corpuscles multiply by quaternary division (Fig. II. 10)
and form groups of four or of four sets of four symmetrically
arranged. The division of the chlorophyll corpuscles is not
necessarily followed by that of the protoplasm, and accordingly
specimens are found with many chlorophyll corpuscles embedded
in a large growth of protoplasm (Fig. II. 8) ; the growth may increase
to a considerable size, numbering some hundreds of chlorophyll
corpuscles, and a proportionate development of protoplasm. Such
a growth is not a plasmodium, that is to say, is not formed by
fusion of independent amoeba forms, but is due to continuous
growth. When nutrition fails the individual chlorophyll corpuscles
separate, each carrying with it an investment of protoplasm, and
then each such amoeba form forms a cyst around itself which is
covered with short spines (Fig. II. 9). The cysts are not known
to give rise to spores, but appear to be merely hypnocysts.

The domination of the protoplasm by the chlorophyll corpuscles
is very remarkable and unlike anything known in any other
organism. Possibly the chlorophyll corpuscles are to be regarded
as nuclei, since it is known that there are distinct points of affinity
between the dense protoplasm of ordinary nuclei and the similarly
dense protoplasm of normal chlorophyll corpuscles.

CLASS II. MYCETOZOA, De Bary.

Characters. Gymnomyxa which, as an exception to all other
Protozoa, are not 'inhabitants of water but occur on damp surfaces
exposed to the air. They are never parasitic, as are some of the
Proteomyxa most nearly allied to them (Plasmodiophora, &c.), but
feed on organic debris. They are structurally characterized by the
fact that the amoeba forms, which develop either directly or through
flagellulse from their spores, always form large, sometimes very
large, i.e., of several square inches area, fusion plasmodia (or
rarely aggregation plasmodia), and that the spores are always
chlamydospores (i.e., provided with a coat) and are formed either
in naked groups of definite shape (sori) or on the surface of peculiar
columns (conidiophors) or in large fruit-like cysts which enclose the
whole or a part of the plasmodium and develop besides the spores
definite sustentacular structures (capillitium) holding the spores in
a mesh- work.

Three orders of Mycetozoa are distinguishable according to the
arrangement of the spores in more or less complex spore-fruits.

ORDER 1. SOROPHORA, Zopf.

Characters. Mycetozoa which never exhibit a vibratile (mouadi-
form) swarmspore or ttagellula phase, but hatch from the spore as
amoeba;. A true fusion plasmodium is not formed, but an aggrega-
gation plasmodium by the contact without fusion of numerous
amceba forms. The spore fruit is a naked aggregation of definitely
arranged encysted amoeba; called a sorus, not enclosed in a common
capsule ; each encysted amceba has the value of a single spore and
sets free on germination a single amcebula. They inhabit the dung
of various animals.

Genera. Copromyxa, Zopf; Cynlliulina, Cicnk. ; Dictyostelium,
Brefeld ; Acrasis, Van Tieghem ; Polyspondylium, Brefeld.

ORDER 2. ENDOSPOREA, Zopf.

Characters. Mycetozoa always passing through the flagellula
phase and always forming true plasmodia by fusion of amceba
forms. The spore-fruit is in the form of a large cyst which encloses
a quantity of the plasmodium ; the latter then breaks up into (a)

12

PROTOZOA

spores (one corresponding to each nucleus of the enclosed plas-
modium) each of which has a cellulose coat, and (b) a capillitium
of threads which hold the spores together. Each spore (chlamydo-
spore) liberates on germination a single mieleated flagellula, which
develops into an amcebula, which in turn fuses with other amcebulie
to form the plasmodium. The Endosporea are essentially dwellers
on rotten wood and such vegetable refuse.

FIG. III. Mycetozoa (after DeBary). 1-6. Germination of spore(l) of Trichta
varia, showing the emerging "flagellula" (4, 5), and its conversion into an
"amcebula" (6). 7-18. Series leadintr from spore to plasmodium phase of
Chondrioderma difforme: 7, spore; 10, flagellula; 1'2, amcebula; 14, apposi-
tion of two amcebulaB ; 15-17, fusions ; 18, plasmodium. 19, 20, Spore-fruit
(cyst) of Ptiysarum JcueopfuEum, Fr. (x 25), the former from the surface, the
latter in section with the spores removed to show the sustentacular network or
capillitium. 21. Section of the spore-cyst of Didymium squaintilosum,viith the
spores removed to show the radiating capillitium x and the stalk.

Sub-order 1. PERITHICHEA, Zopf.

Fain. 1. CLATHROPTYCHIACEJE, Rostafinski.

Genera. Clathroptyckium, Rost. ; Enteridium, Ehr.
Fam. 2. CniBRARiACE^;.

Genera. Dictydium, Pers. ; Cribraria, Pers.

Sub-order 2. EXDOTRICHEA, Zopf.

Fam. 1. PHYSAREA.

Genera. Physarum, Pers.; Craterium, Trentepol; Eadliamia,
Berkeley ; Leocarpiis, Link. ; Tilmadochc, Fr. ; Fuligo
(slSthalium), Hall ; ^Ethaliopsis, Z.
Fam. 2. DIDYMIACE.E.

Genera. Didymium; Lepidodcrma, DeBary.
Fam. 3. SpUMAKIACEai.

Genera. Spuniaria, Pers. ; Diachca, Fries.
Fam. 4. STEMONITEA.

Genera. Stemonitis, Gleditsch ; Comatricfta, Preuss ; Lam-

prodcrma, Rost.
Fam. 5. ENERTHKNEMEA.

Genera. Enerthema, Bowman.
Fam. 6. RETICULARIACE.E, Zopf.

Genera. Amauroch&te, Rost; Selwularia, Bull.
Fam. 7. TRICHINACE^;.

Genera. ffemiarcyria, Rost. ; Trichia, Hall.
Fam. 8. ARCYRIACEJE.

Genera. Arcyria, Hall; Cornuvia, Rost.; Lycor/ala, Ehr.
Fam. 9. PERicH^NACEi;.

Genera. Perich&na, Fries. ; Lachnobolus, Fries.
Fam. 10. LICEACE^E.

Genera. Licca, Schrader ; Tiibulina, Pers.: Lindbladia,
Fries. ; TubuUfcra, Zopf.

ORDER 3. EXOSPOREA, Zopf.

Characters. The chlamydospore liberates an amcebula iu the
first instance, which develops into a flagellula. This subsequently
returns to the amceba form, and by fusion with other amxBbulse it
forms a true fusion plasmodium. The spores are not produced
within a cyst but upon the surface of column-like up-growths of the
plasmodium, each spore (conidum) forming as a little spherical out-
growth attached to the column (conidiophor) by a distinct pedicle.

Sole Genus. Ceratium, [This name must be changed, since it
was already applied to a genus of Dinoflagellata, when Famintziu
and Worouin gave it to this Mycetozoon.]

Further Remarks on Mycetozoa. About two hundred species of
Mycetozoa have been described. Botanists, and especially those who
occupy themselves with Fungi, have accumulated the very large

mass of facts now known in reference to these organisms ; never-
theless the most eminent botanist who has clone more than any
other to advance our knowledge of Myeetozoa, namely, De Bary, has
expressed the view that they are to be regarded rather as animals
than as plants. The fact is that, once the question is raised, it
becomes as reasonable to relegate all the Gymnomyxa without
exception to the vegetable kingdom as to do so with the Mycetozoa.
Whatever course we take with the latter, we must take also with
the Heliozoa, the Radiolaria, and the Reticularia.

The formation of plasmodia, for which the Mycetozoa are conspicu-
ous, appears to be a particular instance of the general phenomenon
of cell-conjugation. Small plasmodia are formed by some of the
Proteomyxa ; but among the other Gymnomyxa, excepting Myceto-
zoa, and among Corticate Protozoa, the fusion of two individuals
(conjugation scum stricto) is more usual than the fusion of several.
Zopf (13) has attempted to distinguish arbitrarily between conjuga-
tion and plasmodium formation by asserting that in the former
the nuclei of the cells which fuse are also fused, whereas in the
latter process the nuclei retain their independence. Both state-
ments are questionable. What happens to the nucleus in such
conjugations as those of the Gregarinre has not yet been made out,
whilst it is only quite recently that Strasburger (30) has shown
that the plasmodia of Mycetozoa contain numerous scattered nuclei,
and it is not known that fusion does not occur between some of
these. There is no doubt that the nuclei of plasmodia multiply
by fission, though we have no detailed account of the process.

The Sorophora are exceptional in that the amoeba? which unite to
form a cell-colony iu their case do not actually fuse but only remain
in close contact ; with this goes the fact that there are no large
spore-cysts, but an identification of spore and spore-cyst. The
amcebie arrange themselves in stalked clusters (sori), and each be-
comes encysted : one may, in this case, consider the cyst equally as
a spore or as a spore-cyst which produces but a single spore. The
amceba; described by various writers as inhabiting the alimentary
canal and the dung of higher animals (including man) belong to
this group. The form described by Cunningham in the Quart.
Jour. Micr. Sci., 1881, as Protomyxomyces coprinarius is appa-
rently related to the Copromyxa (Gitttulina) protca of Fayod (31).

The spore-fruits of the Endosporese occur in various degrees of
elaboration. Usually they are (1) spherical or pear-shaped cysts
with or without an obvious stalk (Fig. III. 19, 20, 21), and often
have a brilliant colour, and are of a size readily observed by the
naked eye, the plasmodia which give rise to them being by no
means microscopic. But they may present themselves (2) as
irregular ridges growing up from the plasmodium, when they are
termed serpula forms. Lastly, the cysts may be united side by
side in larger or smaller groups instead of forming at various sepa-
rate points of the plasmodium. These composite bodies are termed
"fruit-cakes" or sthalia," in view of the fact that the spore-cysts
of Fuligo, also called jEthalium the well-known "flowers of tan"
form a cake of this description.

The capillitium or network of threads which lies between the
spores in the spore-cysts of Endosporeie is a remarkable structure
which exhibits special elaborations in detail in different genera, here
not to be noticed for want of space. Although definite in form and
structure, these threads are not built up by cells but are formed
by a residual protoplasm (cf. Sporozoa) which is left in the cyst
after the spores have been segregated and enclosed each in its
special coat. They are often impregnated by calcium carbonate,
and exhibit crystalline masses of it, as does also the cyst-wall.

The spores of the Mycetozoa are as a rule about the T-sVoth inch
in diameter. They are produced by millions in the large fruit-
cakes of such forms as Fuligo. Often the spore-coat is coloured ; it
always consists of a substance which gives the cellulose reaction
with iodine and sulphuric acid. This has been sometimes con-
sidered an indication of the vegetable nature of the Mycetozoa, but
cannot be so regarded since many animals (especially the Tunieata
and various Protozoa) produce substances giving this same reaction.

Dryness, low temperature, and want of nutriment lead to a dor-
mant condition of the protoplasm of the plasmodium of many
Mycetozoa and to its enclosure in cyst-like growths known as
"sclerotia," which do not give rise to spores, but from which the
protoplasm creeps forth unaltered when temperature, nutrition, and
moisture are again favourable. The sclerotia are similar in nature
to the hypnocysts of other Protozoa.

The physiological properties chemical composition, digestive
action, reaction to moisture, heat, light, and other physical influ-
ences of the plasmodia of Mycetozoa have been made the subject
of important investigations ; they furnish the largest masses of
undirTerentiated protoplasm available for such study. The reader
is referred to Zopf's admirable treatise (13) as to these matters, and
also for a detailed account of the genera and species.

CLASS III. LOBOSA, Carpenter.

Characters. Gymnomyxa in which (as in the succeeding four
classes) the amoeba-phase predominates over the others iu perma-
nence, size attained, and physiological importance. The pseudo-

PROTOZOA

podia are loboso, ranging in form from mere wave-like bulgings
of the surface to blunt finger-like processes, but never having the
character of filaments either simple, arborescent, or reticulate.
Fusions of two individuals (conjugation) have been observed in a

Fio. IV. Various Lobosa. 1, 2, 3. Daclylosphxra (Ainoeba) polypodia, M.
Schultze, in three successive stages of division; the changes indicated
occupied fifteen minutes, a, nucleus ; b, contractile vacuole (copied from
F. E. Schultze, in Archivf. Milcratk. Anat.). 4. Amoeba princeps, Ehr.

(after Auerbach). a, nucleus ; 6, c, vacuoles (one or more contractile ; the
shaded granules are food-particles). 5. Pelomyxa palustns, Greeff

(after Greeff), an example with comparatively few food-particles (natural
size ^,th inch in length). 6. Portion of a Pelomyxa more highly magni-

fied, a, clear superficial zone of protoplasm (so-called " exoplasm ") ; b,
vacuoles, extremely numerous ; c, lobose pseudopodium ; d, a similar
pseudopodium ; e, nuclei ; /, " refractive bodies " (reproductive ?) ; scattered
about in the protoplasm are seen numerous cylindrical crystals. 7.

Arcella vulgaris, Ehr. a, shell; b, protoplasm within the shell ; c, extended
protoplasm in the form of lobose pseudopodia ; d, nuclei; e, contractile
vacuole ; the dark bodies unlettered are gas vacuoles. 8. Cochlio-

podium pellucidum, Hert. and Less, a, nucleus surrounded by a hyaline
halo sometimes mistaken for the nucleus, whilst the latter is termed
nucleolus.

few cases, but not fusions of many individuals so as to form
plasmodia ; nevertheless the size attained by the naked protoplasm
by pure growth is in some cases considerable, forming masses readily
visible by the naked eye (Pelomyxa). The presence of more than.

one nucleus is a frequent character. A contractile vacuole may or
may not be present. The formation of sporocysts and of chlamydo-
sporcs (coated spores) has not been observed in any species, but
naked spores (llagellulo; or amccbulae) have been with more or
less certainty observed as the product of the breaking up of some
species (Amosba? Pelomyxa). The cyst phase is not unusual, but
the cyst appears usually to be a hypnocyst and not a sporocyst.
In the best observed case of spore-production (Pelomyxa) the spores
were apparently produced without the formation of a cyst. Repro-
duction is undoubtedly most freely effected by simple fission
(Amoeba) and by a modified kind of bud-fission (Arcella). Fresh-
water and marine. Two orders of the Lobosa are distinguished in
accordance with the presence or absence of a shell.

ORDER 1. NUDA.

Characters. Lobosa devoid of a shell.

Genera. Ama>ba, Auct. (Fig. IV. 4); Ouramtxba, Leidy (with a
villous tuft at one end, Wallich's A. villosa) ; Cort/cia, Duj. (low,
ridge-like pseudopodia); Lithamceba, Lankester (Fig. V.); Dina-
mceba, Leidy (92) (covered with short stitf processes) ; Hyalodiscus,
H. and L. ; Plakojms, F. E. Schultze ; Dactylosph&m, H. and L.
(Fig. IV. 1, 2, 3); Pelomyxa, Greeff (Fig. IV. 5, 6) ; Amphizonella,
Greeff (forms a gelatinous case which is broken through by the
pseudopodia).

ORDER 2. TESTACEA.

Characters. Lobosa which secrete a shell provided with an
aperture from which the naked protoplasm can be protruded. The
shell is either soft and membranous, or strengthened by the in-
clusion of sand-particles, or is hard and firm.

Genera. CochHopodimn (Fig. IV. 8), H. and L. ; Pyxidicula,
Ehr. ; Arcella, Ehr. (Fig. IV. 7) ; Hyalosphenia, Stein ; Quad-
rula, F. E. Schultze (shell membraneous, areolated) ; Difflugia,
Leclerc (shell with adventitious particles).

Further remarks on the Lobosa. The Lobosa do not form a very
numerous nor a very natural assemblage. Undoubtedly some of
the forms which have been described as species of Amreba are
amoeba forms of Mycetozoa ; this appears to be most probably the
case in parasitic and stercoricolous forms. But when these are
removed, as also those Proteomyxa which have pseudopodia of
varying character, at one time lobose and at another filamentous,
we have left a certain small number of independent lobose
Gymnomyxa which it is most convenient to associate in a
separate group. We know very little of the production of spores
(whether it actually obtains or not) or of developmental phases
among these Lobosa. The common Amcelxe are referable to the
species A. princeps, A. lobosa, Dactylosp/tasra polypodia, Ouramcela
villosa. Of none of these do we know certainly any reproductive
phenomena excepting that of fission (see Fig. IV. 1, 2, 3). Various
statements have been made pointing to a peculiar change in the
nucleus and a production of spores having the form of minute
Amceba?, arising from that body ; but they cannot be considered
as established. Whilst the observed cases of supposed reproduc-
tive phenomena are very few, it must be remembered that we have
always to guard (as the history of the Ciliata has shown, see
below) against the liability to mistake parasitic amcebulje and
flagellulse for the young forms of organisms in which they are
merely parasitic. The remarkable Pelomyxa palustns of Greeff (32)
was seen by him to set free (without forming a cyst) a number of
amcebulie which he considers as probably its young. Mr Weldon
of St John's College, Cambridge, lias observed the same pheno-
menon in specimens of Pelomyxa which made their appearance in
abundance in an aquarium in the Morphological Laboratory,
Cambridge. It seems probable that the amcebulffi in this case are
not parasites but spore-like young, and this is the best observed
case of such reproduction as yet recorded in the group.

Arcella is remarkable for the production of bud-spores, which
may be considered as a process intermediate between simple fission
and the complete breaking up of the parent body into spores. As
many as nine globular processes are simultaneously pinched off from
the protoplasm extruded from the shell of the Arcella ; the nuclei
(present in the parent Arcella to the number of two or three) have
not been traced in connexion with this process. The buds then be-
come nipped off, and acquire a shell and a contractile vacuole (33).

The presence of more than one nucleus is not unusual in Lobosa,
and is not due to a fusion of two or more uninuclear individuals,
but to a multiplication of the original nucleus. This has been
observed in some Amcebas (A. princeps'!) as well as Arcella.
Pelomyxa (Fig. IV. 6) has a great number of nuclei like the Helio-
zoon, Actinosphserium (Fig. VIII.).

Pelomyxa is the most highly differentiated of the Lobosa. The
highly vacuolated character of its protoplasm is exhibited in a less
degree by Lithamreba and resembles that of Heliozoa and Radiolaria.
Besides the numerous nuclei there are scattered in the protoplasm
strongly refringent bodies (Fig. IV. 6,/), the significance of which
has not been ascertained. The superficial protoplasm is free from
vacuoles, hyaline, and extremely mobile. Occasionally it is drawn

14

PROTOZOA

out into very short fane filaments. Scattered in the protoplasm are
a number of minute cylindrical crystals, of unascertained composi-
tion. Pelomyxa is of very large size for a Protozoou, attaining a
diameter of iVth of an inch. It takes into its substance a quantity
of foreign particles, both nutrient organic matter such as Rotifera
and Diatoms and sand particles. It occurs not uncommonly in old

FIG. ~V. Lithamceba, discus, Lank, (after Lankester, 34). A, quiescent ; B,
throwing out pseudopodia. c.v., contractile vacuole, overlying which the
vacuolated protoplasm is seen ; cone, concretions insoluble in dilute HC1
and dilute KHO, hut soluble in strong HC1 ; n, nucleus.

muddy ponds (such as duck-ponds), creeping upon the bottom, and
has a white appearance to the naked eye. Lithamceba (Fig. V.) is
distinguished by its large size, disk-like form, the disk-like shape of
its pseudopodia, the presence of specific concretions, the vacuolation
of its protoplasm, and the block-like form and peculiar tessellated
appearance of its large nucleus, which has a very definite capsule.
In Lithamceba it is easy to recognize a distinct pellicle or temporary
cuticle which is formed upon the surface of the protoplasm, and
bursts when a pseudopodium is formed. In fact it is the rupture of
this pellicle which appears to be the proximate cause of the outflow
of protoplasm as a pseudopodium. Probably a still more delicate
pellicle always forms on the surface of naked protoplasm, and in the
way just indicated determines by its rapture the form and the
direction of the "flow" of protoplasm which is described as the "pro-
trusion" of a pseudopodium.

The shells of Lobosa Testacea are not very complex. That of
Arcella is remarkable for its hexagonal areolation, dark colour, and
firm consistence ; it consists of a substance resembling chitin.
That of Diftlugia has a delicate membranous basis, but includes
foreign particles, so as to resemble the built-up case of a Caddis
worm.

Arcella is remarkable among all Protozoa for its power of secret-
ing gas-vacuoles (observed also in an Amoeba by Biitschli), which
serve a hydrostatic function, causing the Arcella to float. The gas
can be rapidly absorbed by the protoplasm, when the vacuole neces-
sarily disappears and the Arcella sinks.

CLASS IV. LABYEINTHULIDEA.

Characters. Gymnomyxa forming irregular heaps of ovoid
nucleated cells, the protoplasm of which extends itself as a branching
network or labyrinth of line threads. The oval (spindle-shaped)
corpuscles, consisting of dense protoplasm, and possessing each a
well-marked nucleus (not observed in Chlamydomyxa), travel regu-
larly and continuously along the network of filaments. The oval
corpuscles multiply by fission ; they also occasionally become
encysted and divide into four spherical spores. The young forms
developed from these spores presumably develop into colonies, but
have not been observed.

Genera. Two genera only of Labyrinthulidca are known :
I&byrinthula, Cicnkowski ; Chlamydomyxa, Archer.

Cienkowski (35) discovered Labyrinthula on green Alga; growing
on wooden piles in the harbour of Odessa (marine). It has an
orange colour and forms patches visible to the naked eye. Chlamy-
domyxa was discovered by Archer of Dublin (36) in the cells of
Sphagnum and crawling on its surface ; hence it is a freshwater
form. Unlike Labyrinthula, the latter forms a laminated shell of
cellulose (Fig. VI. 2, c), in which it is frequently completely
enclosed, and indeed has rarely been seen in the expanded
labyrinthine condition. The laminated cellulose shells are very
freely secreted, the organism frequently deserting one and forming
another within or adherent to that previously occupied. The
network of Chlamydomyxa appears to consist of hyaline threads of
streaming protoplasm, whilst that of Labyrinthula has a more
horny consistence, and is not regarded by Cienkowski as protoplasm.

The spindle-shaped cells are much alike in form and size in the
two genera; but no nucleus was detected by Archer in those of
Chlamydomyxa. The encysting of the spindle-cells and their
fission into spores has been seen only in Labyrinthula. Chlamy-
domyxa is often of a brilliant green colour owing to the presence of
chlorophyll corpuscles, and may exhibit a red or mottled red and
green appearance owing to the chemical change of the chlorophyll.

It has been observed to take in solid nourishment, though Labyiin-
thula has not.

The Labyrinthulidea present strong resemblances to the Myceto-
zoa. The genus Daetylostelium (Sorophora) would come very close
to Labyrinthula were the amcebfe of its aggregation plasmodium

Fjrt. VI. Labyrinthulidea. 1. A colony or "cell-heap" of Labi/riui/niln
ritfllhia, Cirnk., cniwlin^ upon an Alga. 2. A colony or " cell-heap"

of Chlauii/iliitiii/xn labyrinthuloides, Archer, with fully expanded network
of thread's on which tlie oat-shaped corpuscles (cells) are moving, o is an
invested food particle ; at c a portion of the general protoplasm has
detached itself and become encysted. 3. A portion of the network of

Labyrinthula ritdlina, Cienk., more highly magnified, p, protoplasmic
mass apparently produced by fusion of several filaments ; p', fusion of
several cells which have lost their definite spindle-shaped contour ; s,
corpuscles which have become spherical and are no longer moving (perhaps
about to be encysted). 4. A single spindle cell and threads of Labii-

rintltuln macrocosm's, Cienk. n, nucleus. 5. A group of encysted cells

of L. maerocystis. embedded in a tough secretion. (i, 7. Encysted cells

of L. macrocystis, with enclosed protoplasm divided into four spores.
8. 9. Transverse division of a non-encysted spindle-cell of L. macrocystis.

set upon a network of threads. Such a network, whether in the
condition of soft protoplasm or hardened and horny, is represented
in the higher Mycetozoa by the capillitium of the sporocysts.

The most important difference between Archer's Chlamydomyxa
and Cienkowski's Labyrinthula is that in the former the threads

PROTOZOA

15

of the network appear to consist of contractile protoplasm, whilst
in the latter they are described as firm horny threads exuded by
the spindle-cells. Neither form has been re-examined since its
discovery ; and it is possible that this apparent difference will be
removed by further study.

FIG. VII. Heliozoa. 1. Aetinophrys sol, Ehrli. ; x SOO. a. food-particle
lying in a large food-vacuole ; b, deep-lying finely granular protoplasm ; c,
axial filament of a pseudopodium extended inwards to the nucleus; d, the
central nucleus ; e, contractile vacuole ; /, superficial much-vacuolated
protoplasm. 2. Clathndina clegaiis, Cienk. ; X 200. 3. Hetcr-

ophrys marina, H. and L. x 660. a, nucleus ; b, clearer protoplasm
surrounding the nucleus; c, the peculiar felted envelope. 4. /Vrc//A<'-

diophrys pallida, F. E. Schultze ; x 430. a, food-particle ; b, the nucleus ;
c, contractile vacuole ; it, central granule in which all the axis-filaments of
the pseudopodia meet. The tangentially disposed spicules are seen
arranged in masses on the surface. 5. Acanthoc'/stis turfacea, Carter;

X 240. a, probaldy the central nucleus ; b, clear protoplasm around the
nucleus ; c, more superficial protoplasm with vaeuoles and chlorophyll
corpuscles ; d, coarser siliceous spicules ; e, finer forked siliceous spicules ;
/, finely granular layer of protoplasm. The long pseudopodia reaching
beyond the spicules are not lettered. C. Hi-flagellate "flagellula" of

Acunthacystis aculeata. a, nucleus. 7. Ditto of Clathrulina elegans.

a, nucleus. 8. Astroilisculus ruber, Green* ; x 320. a, red-coloured

central sphere (? nucleus) ; b, peripheral homogeneous envelope.

CLASS V. HELIOZOA, Haeckel, 1866.

Characters. Gymnomyxa in which the dominating amoeba phase
has the form of a spherical body from the surface of which radiate

numerous isolated filamentous pseudopodia which exhibit very little
movement <>r change <>( form, except when engaged in the inception
of food-particles. The protoplasm of the spherical body is richly
vacuolated ; it may exhibit one or more contractile vaeuoles and
either a single central nucleus or many nuclei (Nuclearia, Aetino-
sphterium). Skeletal products may or may not be present. Flagi-1-
lulaj have been observed as the young forms of some species (Acan-
thocystis, Clathrulina), but very little has been as yet ascertained
as to spore-formation or conjugation in this group, though isolated
facts of importance have been observed. Mostly freshwater forms.

II

FIG. Till. Heliozoa. 1. AcKnospluerium EicliJiornii, Ehr. ; x 200. a,
nuclei ; b, deeper protoplasm with smaller vaeuoles and numerous nuclei ;

c, contractile vaeuoles ; rf, peripheral protoplasm with larger vaeuoles.
2. A portion of the same specimen more highly magnified and seen in
optical section, a, nuclei ; b, deeper protoplasm (so-called endosarc);

d, peripheral protoplasm (so-called eetosarc); e, pseudopodia showing the
granular protoplasm streaming over the stitf axial filament ; /, food-
particle in a food-vacuole. 3, 4. Nuclei of Actinosphrcrium in the
resting condition. 5-13. .Successive stages in the division of a
nucleus of Actinosphrcriuni, showing fibrillation, and in 7 and 8 formation
of an equatorial plate of cliroinatin substance (after Hertwig). 14.
Cyst-phase of Actum-i'ti^'i-hnii BicAAomii, showing the protoplasm
divided into twelve chlamyduspores, each of which has a siliceous coat ;
a, nucleus of the spore ; g, gelatinous wall of the cyst ; ft, siliceous coat of
the spore.

16

PROTOZOA

ORDER 1. APHROTHORACA, Hertwig (56).
Characters. Heliozoa devoid of a spicular or gelatinous envelope,
excepting in some a temporary membranous cyst.

Genera. Nuclearia, Cienk. (37) (many nuclei ; many contractile
vacuoles ; body not permanently spherical, but amreboid) ; Actin-
ophrys, Ehr. (Fig. VII. 1 ; body spberical ; pseudopodia with an
axial skeletal filament ; central nucleus ; one large contractile
vacuole; often forming colonies ; A. sol, the Sun -animalcule);
Actinosph&rium, Stein (Fig. VIII. ; spherical body ; pseudopodia
with axial filament ; nuclei very numerous ; contractile vacuoles 2
to 14) ; Actinoloplius, F. E. Schulze (stalked).

ORDER 2. CHLAMYDOPHORA, Archer (57).

Characters. Heliozoa with a soft jelly-like or felted fibrous
envelope.

Genera. Hcterophrys, Archer (Fig. VII. 3); Sphxtiastrum,
Greeff; Astrodiscuhis, Greeff(Fig. VII. 8).

ORDER 3. CHALAROTHORACA, Hertw. and Lesser (58).

Characters. Heliozoa with a loose envelope consisting of isolated
siliceous spieules.

Genera. Raphidiophrys, Archer (Fig. VII. 4 ; skeleton in the
form of numerous slightly curved spieules placed tangeutially in
the superficial protoplasm) ; Pompholyxophrys, Archer; Pinacocystis
H. and L. ; Pinaciophora, Greeff ; Acanthoeystis, Carter (skeleton
in the form of radially disposed siliceous needles ; encysted con-
dition observed, and flagellula young, Fig. VII. 6) ; WagnerMa,
Meresch.

ORDER 4. DESMOTHORACA, Hertw. and Less.

Characters. Heliozoa with a skeletal envelope in the form of a
spherical or nearly spherical shell of silica preforated by numerous
large holes.

Genera. Orbulinella, Entz (without a stalk) ; Clalhrulina,
Cienk. (with a stalk, Fig. VII. 2).

Further remarks mi the ffeliozoa. The Sun-animalcules, Actino-
phrys and Actinosphaerium, were the only known members of this
group when Carter discovered in 1863 Acanthoeystis. Our further
knowledge of them is chiefly due to Archer of Dublin, who dis-
covered the most important forms, and figured them in the Quart.
Jour. Micr. Sci. in 1867.

Some of the Proteomyxa (e.g., Vampyrella) exhibit " heliozoon-
like" or " nctinophryd " forms, but are separated from the true
Heliozoa by the fact that their radiant pseudopodia are not main-
tained for long in the stiff isolated condition characteristic of this
group. It is questionable whether Nuclearia should not be relegated
to the Proteomyxa on account of the mobility of its body, which in
all other Heliozoa has a constant spherical form.

Actinophrys sol is often seen to form groups or colonies (by
fission), and so also is Raphidiophrys. It is probable from the
little that is known that reproduction takes place not only by
simple fission but by multiple fission, producing flagellate spores
which may or may not be preceded by eucystment. Only Clath-
rulina, Acanthoeystis, Actinosphserium, and Aetinophrys have
been observed in the encysted state, and only the first two have
been credited with the production of flagellated young. The two
latter genera form covered spores within their cysts, those of Actino-
sphferium being remarkable for their siliceous coats (Fig. VIII.
14), but their further development has not been seen.

CLASS VI. EETICULARIA, Carpenter, 1862.
(Foraminifera, Auct. , Thalamophom. Hertwig).

Characters. Gymnomyxa in which the dominating amoeba-
phase, often of great size (an inch in diameter), has an irregular
form, and a tendency to throw out great trunks of branching and
often anastomosing filamentous pseudopodia, and an equally strong
tendency to form a shell of secreted membrane or secreted lime or of
agglutinated sand particles (only in one genus of secreted silex) into
Which the protoplasm (not in all ?) can be drawn and out of and
over which it usually streams in widely spreading lobes and
branches. One nucleus is present, or there are many. A contrac-
tile vacuole is sometimes, but not as a rule, present (or at any rate
not described). Reproduction is by fission and (as in some other
Protozoa) by the formation of peculiar bud-spores which remain
for a time after their formation embedded in the parental proto-
plasm. No multiple breaking up into spores after or independent
of the formation of a cyst is known. Marine and freshwater.

The Keticularia are divisible into several orders. The marked
peculiarity of the shell structure in certain of these orders is only
fitly emphasized by grouping them together as a sub-class Per-
forata, in contrast to which the remaining orders stand as a
sub-class Imperforata. The distinction, however, is not an ab-
solute one, for a few of the Lituolidea are perforate, that is, are
sandy isomorphs of perforate genera such as Globigerina and
Rotalia.

Fio. IX. Gromiidea (Eeticularia membranosa)- l.
Archeri, Barker, a, nucleus; b, contractile vacuoles; c, the yellow oil-like
Ijotly. Moor pools, Ireland. 2. Gromia ovtformis, Duj. a, the

numerous nuclei ; near these the elongated bodies represent ingested
Diatoms. Freshwater. 3. Shcpheardella ttvnuformis, Siddall (yitart.
Jour. Micr. Sci., 1880); X 30 diameters. Marine. The protoplasm is
retracted at both ends into the tubular case. CT, nucleus. 5. Skep-

heardella taniiformis; x 15; with pseudopodia fully expanded.
6-10. Varying appearance of the nucleus as it is carried along in the
streaming protoplasm within the tube. 11. Amphitrema Wrightianum,
Archer, showing membranous shell encrusted with foreign particles.
Moor pools, Ireland. 12. Diaplwrophodon mobile, Archer, a, nucleus.
Moor pools, Ireland.

SUB-CLASS A. Imperforata.

Characters. Shell-substance not perforated by numerous aper-
tures through which the protoplasm can issue, but provided with
only one or two large apertures, or in branched forms with a few
such apertures.

ORDER 1. GROMIIDEA, Brady.

Characters. Shell or test membranous, in the form of a simple
sac with a pseudopodial aperture either at one extremity or at both.
Pseudopodia thread-like, long, branching, reticulated. Marine and
freshwater.

Fam. 1. MONOSTOMINA, with a single aperture to the shell.

PROTOZOA

17

Genera. licbcrkulinia, Clap, and Lach. ; Gromin. Tin']. (Fig.
IX. 2) ; MikfiHiniiiiin, Hert\v. ; EughjpJia, Duj. (shell built up of
hexagonal siliceous plates) ; Diajthuni/ilwilim, Archer (38) (many
foreign (articles cemented to form shell ; small pseudopodia issue
between these, hence resembling Perforata, and large long ones from
the proper mouth of the shell, Fig. IX. 12).

FlG. X. Imperforata. 1. Spirolocullnaplamilata, Lamarck, showing five
"coils"; porcellanous. 2. Young ditto, with shell dissolved and

protoplasm stained so as to show the seven nuclei n. 3. Spirolina (Pene-
roplis) ; a sculptured imperfectly coiled shell ; porcellanous. 4.

Vertebralina, a simple shell consisting of chambers succeeding one another
in a straight line; porcellanous. 5, 6. Thiirammfna papillata, Brady, a
sandy form. 5 is broken open so as to show an inner chamber; recent,
x 25. 7. Lituola (Haplophragmium) canarietms, a sandy form;

recent, 8. Nucleated reproductive bodies (bud-spores) of Haliphysema.
9. S'/itammitlfna Ixrfs, M. Schultze ; x 40 ; a simple porcellnnous
Miliolkle. 10. Protoplasmic core removed after treatment with weak

chromic acid from the shell of Haliphysema Tumanovitzii, Bow. n,
vesicular nuclei, stained with hrematoxylin (after Lankester). 11.

Haliphysana TmiKtnnn'tzii ; x 25 diam. ; living specimen, showing the
wine-glass-shaped slvll built up of sand-grains and sponge-spicules, and
the abundant protoplasm p, issuing from the mouth of the shell and
spreading partly over its projecting constituents. 12. Shell of Astro-

rhiza, Ituricvla, Sand.; x J; showing the branching of the test on some of
the rays usually broken away in preserved specimens (original). 13.

Section of the shell of irarsipella, showing thick walls built of sand-
grains.

Fam. 2. AMrmsTOMiNA.with an aperture at each end of the shell.

Genera. }}i/ihi/>liri/.<i, Barker (Fig. IX. 1); Jii/i-fimi, Archer;
Ampliitrcma, Archer (Fig. IX. 11); ,S'/ic/.//c.//v/,7/, Siddall (39)
(membranous shell very lung and cylindrical so as to be actually
tubular, narrowed to a apout at each end, Fig. IX. 3; protoplasm
extended from either aperture, Fig. IX. 5, and rapidly circulating
within the tubular test during life, carrying with it the nucleus
which itself exhibits peculiar movements of rotation, Fig. IX. 6, 7,
8, 9, 10).

ORDER 2. ASTRORHIZIDEA, Brady.

Characters. Test invariably consisting of foreign particles ; it ia
usually of large size and single-chambered, often branched or radiatu
with a pseudopodial aperture to each branch, the test often con-
tinued on to the finer branches of the pscudopodia (Fig. X. 12) ;
never symmetrical. All marine.

Fam. 1. ASTRORHIZINA, Brady. Walls thick, composed of loose
sand or mud very slightly cemented.

Genera. Astrorhizct, Sandahl (Fig. X. 12, very little enlarged);
Pclosina, Brady ; Storthosphaera, Brady ; Dcndrophrya, St. Wright ;
Syrmgammina, Brady.

Fam. 2. PILULININA. Test single-chambered ; walls thick,
composed chiefly of felted sponge -spicules and fine sand, without
calcareous or other cement.

Genera. Pilulina, Carpenter; TcchniteUa, Norman ; Bathy-

ilifni, Sars.

Fam. 3. SACOAMMININA. Chambers nearly spherical ; walls thill,
composed of firmly cemented sand grains.

Genera. Psammosph&ra, Schultze; Sorosphxra, Brady ; Saccam-
mina, M . Sars.

Fam. 4. RHABDAMMINIXA. Test composed of firmly cemented
sand - grains, often with sponge - spicules intermixed ; tubular ;
straight, radiate, branched or irregular ; free or adherent ; with one,
two, or more apertures ; rarely segmented.

Genera. Jaculella, Brady; Marsipclla, Norman (Fig. X. 13) ;
Rhalidammina, M. Sars ; Aschemonclla, Brady ; Bhizammina,
Brady ; Sagenella, Brady ; Botcllina, Carp. ; Haliphysema, Bower-
bank (test wine-glass-shaped, rarely branched, attached by a disk-
like base ; generally beset with sponge-spicules, Fig. X. 11 ; pseudo-
podial aperture at the free extremity). This and Astrorhiza are
the only members of this order in which the living protoplasm has
been observed ; in the latter it has the appearance of a yellowish
cream, and its microscopic structure is imperfectly unknown (61).
In Haliphysema the network of expanded pseudopodia has been
observed by Saville Kent as drawn in Fig. X. 11. Lankester (59)
discovered numerous vesicular nuclei scattered in the protoplasm
(Fig. X. 10, n), and also near the mouth of the shell reproductive
bodies (probably bud-spores) embedded in the protoplasm (Fig. X.
8). Haliphysema was described by Bowerbank as a Sponge, and mis-
taken by Haeckel (60) for a very simple two-cell-layered animal
(Enterozoon), to which he assigned the class name of Physemaria.

ORDER 3. MILIOLIDEA, Brady.

Characters. Test impcrforate ; normally calcareous and porcel-
lanous, sometimes encrusted with sand ; under starved conditions
(e.g., in brackish water) becoming chitinous or chitino-arenaceous ;
at abyssal depths occasionally consisting of a thin homogeneous,
imperforate, siliceous film. The test has usually a chambered
structure, being divided by septa (each with a hole in it) into a
series of loculi which may follow one another in a straight line
(Fig. X. 4) or the series may be variously coiled (Fig. X. 1 and 3).
The chambering of the test does not express a corresponding cell-
segmentation of the protoplasm ; the latter, although growing in
volume as the new shell-chambers are formed, remains one continuous
cell-unit with many irregularly scattered nuclei (Fig. X. 2). The
chambered and septate structure results in this group and in the other
orders from the fact that the protoplasm, expanded beyond the
last-formed chamber, forms a new test upon itself whilst it lies and
rests upon the surface of the old test. The variations in such a
formation are shown in Fig. XII. 1, 2, 3, 4.

Fam. 1. NUBECULARINA. Test free or adherent, taking various
irregular asymmetrical forms, with variable aperture or apertures.

Genera. Squ'ininiiiliiifi, Schultze (Fig. X. 9, showing the ex-
panded pseudopodia) ; yuln-nlni-in, Defrance.

Fam. 2. MIUOLIXA. Shell coiled on an elongated axis, either
symmetrically or in a single plane or inequilaterally ; two cham-
bers in each convolution. Shell aperture alternately during growth
(addition of new chambers) at either end of the shell.

Genera. Biloculina, D'Orb. ; Fabularia, Defrance ; Spirolocu-
lina, D'Orb. (Fig. X. 1, 2) ; MiUoIina, Williamson (Fig. XL).

Fam. 3. HAUERININA. Shell dimorphous ; chambers partly
milioline, partly spiral or rectilinear.

Genera. Artieulina, D'Orb.; Vertebralvna, D'Orb. (Fig X. 4);
Oplilhdliiiidhun. Ktibler ; Ifaufrina, D'( >rb. ; Planix/iii-inn, Seguenza.

Fam. 4. PENEROPUDINA. Shell planospiral or cyclical, some-
times crosier-shaped, bilaterally symmetrical.

Genera. Cornuspira, Schultze ; Pencrup!i, Jlontfort (Fig. X. 3) ;

C

18

PROTOZOA

Orbiculina, Lamarck ; Orbitolites, Lamarck (by a division of the
chambers regularly into chamberlets, and a cyclical mode of growth
which results in shells of the size of a shilling, a very elaborate-
looking structure is produced which has been admirably analysed
by Carpenter (40), to whose memoir the reader is specially referred).

FIO. XI.MilioKna (Triloculina) tenera. Young living animal with ex-
panded pseudopoJia (after Max Schultze). A single nucleus is seen ill the
innermost chamber.

Fam. 5. ALVEOLININA. Shell spiral, elongated in the line of
the axis of the convolution ; chambers divided into chamberlets.
Genxis. Alreolina, D'Orb.

Fam. 6. KERAMOSPHJERINA. Shell spherical ; chambers in con-
centric layers.

Genus. Keramosphaera, Brady.

ORDER 4. LITUOLIDEA, Brady.

Characters. Test arenaceous, usually regular in contour ; septa-
tion of the many-chambered forms often imperfect, the cavity being
labyrinthic. This order consists of sandy isomorphs of the simpler
Miliolidea, and also of the simpler Perforata (Lagena, Nodosaria,
Cristellaria, Globigerina, Rotalia, Nonionina, &c. ) ; it also contains
some peculiar adherent species.

Fam. 1. LITUOLINA. Test composed of coarse sand-grains, rough
externally ; often labyrinthic.

Genera. Reophax, Montfort ; Haplophragmium, Reuss (Fig.
X. 7) ; CosTcinolina, Stache ; Placopsiliiia, D'Orb. ; Haplostiche,
Reuss ; Lituola, Lamarck ; Bdclloidina, Carter.

Fam. 2. TROCHAMMININA. Test thin, composed of minute
sand-grains incorporated with calcareous and other organic cement,
or embedded in a chitinous membrane ; exterior smooth, often
polished ; interior smooth or rarely reticulated ; never labyriuthic.

Genera. Thurammina, Brady (test consisting typically of a
single spherical chamber with several mammillate apertures, Fig.
X. 5, 6) ; Hippocrepina, Parker ; Hormosina, Brady ; Ammo-
discus, Reuss ; Trochammina, Parker and Jones ; Carterina,
Brady; Webbina, D'Orb.

Fam. 3. ENDOTHYRINA. Test more calcareous and less sandy
than in the other groups of Lituolidea ; sometimes perforate ;
septation distinct.

Genera. Nodosinella, Brady ; Polyphragma, Reuss ; Inrolutina,
Terij. ; Endothyra, Phillips ; Bradyina, Moll. ; Stachcia, Brady.

Fam. 4. LOFTUSINA. Test of relatively large size ; lenticular,
spherical, or fusiform ; constructed either on a spiral plan or in
concentric layers, the chamber cavities occupied to a large extent
by the excessive development of the finely arenaceous cancellated
walls.

Genera. Cydammina, Brady ; Loftusia, Brady ; Parkeria,
Carpenter.

SUB-CLASS B. Perforata.

Characters. Shell substance perforated by numerous minute
apertures, through which as well as from the main aperture the
protoplasm can issue.

ORDERS. TEXTULARIDEA, Brady.

Characters. Tests of the larger species arenaceous, either with
or without a perforate calcareous basis ; smaller forms hyaline and
conspicuously perforated. Chambers arranged in two or more
alternating series, or spiral or confused ; often dimorphous.

Fam. 1. TEXTL-LAUINA. Typically bi- or tri-serial ; often bi-
rarely tri-morphous.

Genera. Texlularia Defrance ; Cuneolina, D'Orb. ; Verneiul-
ina, D'Orb. ; Tritaxia, Reuss ; Chrysalidina, D'Orb. ; Bigenerma,
D'Orb.; Pawnina, D'Orb.; Spiroplecta, Ehr. ; Gaudryina, D'Orb.;
Valvulina, D'Orb.; Clamdina, D'Orb.

Fam. 2. BULIMININA. Typically spiral ; weaker forms more 01
less regularly biserial ; aperture oblique, comma-shaped or some
modification of that form.

Genera. Bulimina, D'Orb. ; Virgulina, D'Orb. ; Bifarina,
Parker and Jones ; Bolivina, D'Orb. ; Plcurostomella, Reuss.

Fam. 3. CASSIDULINA. Test consisting of a Textularia-like series
of alternating segments more or less coiled upon itself.

Genera. Cassidulina, D'Orb.; Ehrenbcrgina, Reuss.

ORDER 6. CHILOSTOMELLIDEA, Brady.

Characters. Test calcareous, finely perforate, many-chambered.
Segments following each other from the same end of the long axis,
or alternately at the two ends, or in cycles of three, more or less
embracing. Aperture a curved slit at the end or margin of the final
segment.

Genera. EllipsoiduM, Seguenza; Chilostomclla, Reuss; Allo-
morphiiia, Reuss.

ORDER?. LAGENIDEA, Brady.

Characters. Test calcareous, very finely perforated ; either
single-chambered, or consisting of a number of chambers joined in
a straight, curved, spiral, alternating, or (rarely) branching series.
Aperture simple or radiate, terminal. No interseptal skeleton nor
canal system.

Fam. 1. LAGENINA. Shell single-chambered.

Genera. Lagena, Walker and Boys; Nodosaria, Lamk. ; Lin-
gulina, D'Orb. ; Frondicularia, Defrance ; Rhabdogonium, Reuss ;
Marginulina, D'Orb. ; Vaginulina, D'Orb. ; Bimulina, D'Orb. ;
Cristellaria, Lamk. ; Amphicoryne, ScUumb. ; Lina / ulinopsis,'Re\iss;
Flabellina, D'Orb. ; Amphimorphina, Neugeb. ; Dentalinopsis,
Reuss.

Fam. 2. POLYMORPHININA. Segments arranged spirally or
irregularly around the long axis ; rarely biserial and alternate.

Genera. Polymorphina, D'Orb. ; Dimorphiiia, D'Orb. ; Uviger-
ina, D'Orb. ; Sagrina, P. and J.

Fam. 3. RAMULININA. Shell branching, composed of spherical
or pyriform chambers connected by long stoloniferous tubes.

Genus. Ramulina, Rupert Jones.

ORDER 8. GLOBIGERINIDEA, Brady.

Characters. Test free, calcareous, perforate ; chambers few,
inflated, arranged spirally ; aperture single or multiple, con-
spicuous. No supplementary skeleton nor canal system. All the
larger species pelagic in habit.

Genera. Globigerina, D'Orb. (Fig. XII. 6) : Orbulina, D'Orb
(Fig. XII. 8) ; Hastigerina, Wy. Thomson (Fig. XII. 5) ; Pul-
Unia, P. and J. ; Sphxroidina, D'Orb. ; Candeina, D'Orb.

ORDER 9. ROTALIDEA, Brady.

Characters. Test calcareous, perforate ; free or adherent. Typi-
cally spiral and "rotaliform" (Fig. XII. 2), that is to say, coiled
in such a manner that the whole of the segments are visible on the
superior surface, those of the last convolution only on the Inferior
or apertural side, sometimes one face being more convex sometimes
the other. Aberrant forms evolute, outspread, acervuline, or
irregular. Some of the higher modifications with double chamber-
walls, supplemental skeleton, and a system of canals. The nature
of this supplemental skeleton is shown in Fig. XII. 2 and 10.

Fam. 1. SPIRILLINIXA. Test a complanate, plauospiral, non-
septate tube ; free or attached.

Genus. Spirillina, Ehr.

Fam. 2. ROTALINA. Test spiral, rotaliform, rarely evolute, very
rarely irregular or acervuline.

Genera. Patcllina, Williamson ; Cymbalopora, Hay ; Discorbina,
P. and J. ; Planorbulina, D'Orb. ; Truncatulina, D'Orb. ; Anomal-
ina, P. and J. ; Carpentaria, Gray (adherent) ; Rupcrtia,
Wallick ; Pulvinulina, P. and J. ; Rotalia, Lamk. ; Calcarina,
D'Orb. [Shell rotaliform ; periphery furnished with radiating
spines ; supplemental skeleton and canal system largely developed.
This form is shown in a dissected condition in Fig. XII. 10. Outside
and between the successive chambers with finely perforated walls
a 2 , a 3 , a* a secondary shell-substance is deposited by the proto-
plasm which has a different structure. Whilst the successive
chambers with their finely perforate walls (resembling dentine in
structure) are formed by the mass of protoplasm issuing from the
mouth of the last-formed chamber, the secondary or supplemental-
shell substance is formed by the protoplasm which issues through
the fine perforations of the primary shell substance ; it is not
finely canaliculated, but is of denser substance than the primary
shell and traversed by coarse canals (occupied by the protoplasm)
which make their way to the surface of the test (c' t c"). In Cal-
carina a large bulk of this secondary shell-substance is deposited
around each chamber and also forms the heavy club-like spines.]

Fam. 3. TINOPORINA. Test consisting of irregularly heaped
chambers with (or sometimes without) a more or less distinctly
spiral primordial portion ; for the most part without any general
pseudopodial aperture.

PROTOZOA

Genera. Tinaporns, Carpenter; Gijpsina, Carter ; Ajihrosina,
Carter ; Tlialamojwnt, Rocmcr ; /W////v,, Risso. [Sliell para-
sitic, encrusting, or arborescent ; surfarr uivnl.itol, cnliiiiiTil pink
or white, Fig. XII. 9. Interior partly occupied by small chambers,
arranged in more or less regular layers, and partly by non-
segmented canal-like spaces, often crowded with sponge-spicules
No true canal system. This is one of the most important types as
exhibiting the arborescent and encrusting form of growth. It is
fairly abundant]

10

Fio. XII. Perforata. 1. Spiral arrangement of simple chambers of a
Reticularian shell. 2. Ditto, with double septal walls, ami supple-

mental shell-substance (shaded). 3. Diagram to show the mode in

which successively-formed chambers may completely embrace their pre-
decessors. 4. Diagram of a simple straight series of non-embracing
chambers. 5. Hastigerina (Globitjerina) Murraiji, Wyv. Thomson.
a, bubbly (vacuolated) protoplasm, enclosing 6, the perforated Globi-
gerina-like shell (couf. central capsule of -Radiolaria). From the peripheral
protoplasm project, not only fine pseudopodia, but hollow spines of
calcareous matter, which are set on the shell, and have an axis of active
protoplasm. Pelagic ; drawn in the living state. 6. GlMgeraui
Indloides, D'Orb., showing the punctiform perforations of tho she'll aiul
the main aperture. 7. Fragment of the shell of Globigerina, seen
from within, and highly magnified, a, fine perforations in the inner shell
substances ; b, outer (secondary) shell substance. Two coarser perfora-
tions are seen in section, and one lying among the smaller. 8. Or-
bnlina universa, D'Orb. Pelagic example, with adherent radiating

. , -, , ,

oils in section, showing the thin primary

OKDEU 10. NUMMULINIDEA, Brady.

Characters. Test calcareous and finely tubulated ; typically
free, many-chambered, and symmetrically spiral. The higher
modifications all possess a supplemental skeleton, and canal system
of greater or less complexity.

Fam. 1. FUSULININA. Shell bilaterally symmetrical ; chambers
extending from pole to pole; each convolution completely enclosing
the previous whorls. Shell-wall finely tubulated. Septa single or
rarely double ; no true interseptal canals. Aperture a single
elongated slit, or a row of small rounded pores, at the inner edge
of the final segment.

Genera. Fusulina, Fischer ; Schivagcrina, Holler.

Fam. 2. POLYSTOMELLINA. Shell bilaterally symmetrical, nauti-
loid. Lower forms without supplemental skeleton or interseptal
canals ; higher types with canals opening at regular intervals along
the external septal depressions.

Genera. Nonionina, D'Orb. ; Polystomella, Lamarck.

Fam. 3. NUMMULITINA. Shell lenticular or complanate ; lower
forms with thickened and finely tubulated shell-wall, but no inter-
mediate skeleton ; higher forms with interseptal skeleton and com-
plex canal system.

Genera. Archseodiscus, Brady ; Amphistcgiim, D'Orb. ; Oper-
culina, D'Orb. ; Hctcrostcijina, D'Orb. ; Nummulites, Lamarck ;
Assilina, D'Orb.

Fam. 4. CYCLOCLYPEINA. Shell complanate, with thickened
centre, or lenticular ; consisting of a disk of chambers arranged
in concentric annuli, with more or less lateral thickening of lami-
nated shell substance, or acervuline layers of chamberlets. Septa
double and furnished with a system of interseptal canals.

Genera. Cycloclypeus, Carpenter ; Orbitoidcs, D'Orb.

Fam. 5. EOZOONINA. Test forming irregular, adherent, acervu-
line masses.

Genus. Eo:oon Dawson.

Further remarks on the Ecticularia, The name Thalamophora,
pointing to the peculiar tendency which the larger members of
the group have to form chamber after chamber and so to build up
a complex shell, has been proposed by Hertwig (56) and adopted by
many writers. The old name Foraminifera (which did not refer
to the fine perforations of the Perforata but to the large pseudo-
podial aperture leading from chamber to chamber) has also been
extended by some so as to include the simpler Gromia-like forms.
On the whole Carpenter's term Reticularia (62) seems most suitable
for the group, since they all present the character indicated. It
has been objected that the Radiolaria are also reticular in their
pseudopodia, but if we except the pelagic forms of Reticularia
(Globigerina, Orbulina, &c.), we find that the Radiolaria are really
distinguishable by their stiller, straighter, radiating pseudopodia.
No doubt the Labyrinthulid Chlamydomyxa and the plasmodia of
some Mycetozoa are as reticular in their pseudopodia as the
Reticularia, but they possess other distinctive features which
serve, at any rate in an artificial system, to separate them.

The protoplasm of the majority of the Reticularia is unknown,
or only very superficially observed ; hence we have made a point of
introducing among our figures as many as possible which show this
essential part of the organism. It is only recently (1876) that
nuclei have been detected in the calcareous-shelled members of the
group, and they have only been seen in a few cases.

The protoplasm of the larger shell-making forms is known to be
often strongly coloured, opaque, and creamy, but its minute struc-
ture remains for future investigation. Referring the reader to the
figures and their explanation, we would draw especial attention to
the structure of the protoplasmic body of Hastigeriua (one of the
Globigerinidea) as detected by the "Challenger" naturalists. It
will be seen from Fig. XII. 5 that the protoplasm extends as a rela-
tively enormous "bubbly "mass around the shell which is sunk
within it ; from the surface of this " bubbly " (vacuolated or alveol-
atcd) mass the pseudopodia radiate.

The reader is requested to compare this with Fig. XIII., repre-
senting the "bubbly " protoplasmic body of Thalassicolla. It then
becomes obvious that the perforated central capsule CK of the latter
holds the same relation to the mass of the protoplasm as does the
central perforated shell of Globigerina (Hastigerina). The extreme
vacuolation of the protoplasm in both cases (the vacuoles being

20

PROTOZOA

filled with sea- water accumulated by endosmosis) and the stifl' radiat-
ing pseudopodia are directly correlated with the floatiug pelagic life of
the two organisms. All the Eadiolaria are pelagic, and many exhibit
this vacuolatiori ; only a few of the Reticularia are so, and their struc-
tural correlation to that habit has only lately been ascertained.

The Reticularia are almost exclusively known by their shells,
which otter a most interesting field for study on account of the very
great complexity of form attained by some of them, notwithstand-
ing the fact -that the animal which produces them is a simple uni-
cellular Protozoon. Space does not permit the exposition here of
the results obtained by Carpenter in the study of the complex shells
of Orbitolites, Operculina, Nummulites, &c. ; it is essential that his
work Introduction to the Study of the Foraminifcra (Ray Society,
1862) should be consulted, and in reference to the sandy-shelled
forms the monograph by Brady, in the Challenger Reports, vol. ix. ,
1883 ; and it must be sufficient here to point out the general prin-
ciples of the shell-architecture of the Reticularia. Let us suppose
that we have an ever-growing protoplasmic body which tends to
produce a calcareous shell on its surface, leaving an aperture for the
exit of its pseudopodia. It will grow too large for its shell and
accumulate outside the shell. The accumulated external mass may
then secrete a second chamber, resting on the first as chamber 1
rests on chamber in Fig. XII. 4. By further growth a new
chamber is necessitated, and so is produced a series following one
another in a straight line, each chamber communicating with the
newer one in front of it by the narrow pseudopodial aperture
(a, a 1 , a 2 , a s ). Now it is possible for these chambers to be very
variously arranged instead of simply as in Fig. XII. 4. For instance,
each new chamber may completely enclose the last, as in Fig. XII.
3, supposing the protoplasm to spread all over the outside of the
old chamber before making a new deposit. Again the chambers
need not succeed one another in a straight line, but may be dis-
posed in a spiral (Fig. XII. 1). And this spiral may be a flat coil,
or it may be a helicine spiral with a rising axis ; further it may be
close or open. All these forms in various degrees of elaboration
are exhibited by lliliolidea and various Perforata.

But the Perforata in virtue of their perforate shell-walls introduce
a new complication. The protoplasm issues not only from the
mouth of the last-formed chamber, but from the numerous pores in
the wall itself. This latter protoplasm exerts its lime-secreting
functions ; it gathers itself into coarse branching threads which
remain uucalcified, whilst all around a dense deposit of secondary
or supplemental shell-substance is thrown down, thus producing a
coarsely canalicular structure. The thickness and amount of this
secondary shell and the position it may occupy between and around
the chambers of primitive shell-substance vary necessarily in dif-
ferent genera according to the mode in which the primitive cham-
bers are arranged and connected with one another. Cak-arina is a
fairly typical instance of an abundant secondary shell-deposit (Fig.
XII. 10), audit is the existence of structure resembling the chambers
of Calcarina with their surrounding primary and secondary shell-
substances which has rendered it necessary to regard Eozoon (41) as
the metamorphosed encrusting shell of a pre-Cambrian Reticularian.

The division of the Reticularia iuto Imperforata and Perforata
which is here maintained has no longer the significance which was
once attributed to it. It appears, according to the researches of
Brady, that it is not possible to draw a sharp line between these
sub-classes, since there are sandy forms which it is difficult to
separate from impertbrate Lituolidca and are nevertheless perforate,
in fact are "sandy isomorphs of Lagena, Nodosaria, Globigerina,
and Kotalia. " It does not appear to the present writer that there
can be any insurmountable difficulty in separating the Lituolidca
into two groups those which are sandy isomorphs of the porcel-
lanous Miliolidea, and those which are sandy isomorphs of the
hyaline Perforata. The two groups of Lituolidea thus formed
might be placed in their natural association respectively with the
Imperforata and the Perforata.

The attempt to do this has not been made here, but the classifi-
cation of Brady has been adopted. In Biitschli's large work on the
Protozoa (9) the breaking up of the Lituolidea is carried out to a
logical conclusion, and its members dispersed among the Milinlidi a
on the one hand and the various orders of Perforata on the other hand.

The calcareous shell-substance of the Miliolidea being opaque
and white has led to their being called " Porcellana," whilst the
transparent calcareous shells of the smaller Perforata has gained
for that group the synonym of "Hyalina. "

Tin; shells of the calcareous Reticularia and of some of the
larger arenaceous forms are found in stratified rocks, from the
Palaeozoic strata onwards. The Chalk is in places largely com-
posed of their shells, and the Eocene Nuimmilitic limestone is
mainly a cemented mass of the shells of Nummulites often as
large each as a shilling. The Atlantic ooze is a chalky deposit
consisting largely of the shells of Globigerina, &c.

CLASS VII. RADIOLAEIA, Ilacckel, 1862 (63) (Polyajstina, Ehr.).

Characters. Gymnomyxa in which the protoplasmic body of

the dominant amreba phase has the form of a sphere or cone from

the surface of which radiate filamentous pseudopodia, occasionally
anastomosing, and encloses a spherical (homaxonic) or cone-shaped
(monaxonic) perforated shell of membranous consistence known as
the central capsule, and probably homologous with the perforated
shell of a Globigerina. The protoplasm within the capsule (intra-
capsular protoplasm) is continuous through the pores or apertures
of the capsule with the outer protoplasm. Embedded in the former
lies the large and specialized nucleus (one or more). Gelatinous
substance is frequently formed peripherally by the extracapsular
protoplasm, constituting a kind of soft mantle which is penetrated
by the pseudopodia. A contractile vacuole is never present.

Usually an abundant skeleton, consisting of spicules of silica or
of a peculiar substance called acanthin arranged radially or tangen-
tially, loose or united into a basket-work, is present. Oil globules,
pigment, and crystals are found in greater or less abundance in
the protoplasm.

In most but not all Radiolaria peculiar nucleated yellow cor-
puscles are abundantly present, usually regarded as parasitic Alga?.
Reproduction by fission has been observed, and also in some few
species a peculiar formation of swarm-spores (flagelluke) within the
central capsule, in which the nucleus takes an important part.
All the Radiolaria are marine. The Radiolaria are divided into
two sub-classes according to the chemical nature of their spicular
skeleton, and into orders according to the nature and the disposi-
tion of the apertures in the wall of the central capsule.

EP

FIG. XIII. Thalassicollapelagica, Haeckel; x 25. C'K, central capsule ;
EP, extracapsular protoplasm ; al, alveoli, liquid-holding vacuoles in the
protoplasm similar to those of Heliozoa, Pelomyxa, Hastigerina, &c.; ps,
pseudopodia. The minute unlettered dots are the "yellow cells."

SUB-CLASS I. Silico-Skeleta, Lankcster.

Characters. A more or less elaborate basket-work of tangential
and radial elements consisting of secreted silica is present ; in rare
exceptions no skeleton is developed.

ORDER 1. PEKIPYLYEA, Hertwig.

Characters. Silico-skeletal Radiolaria in which the central cap-
sule is uniformly perforated all over by fine pore-canals ; its form is
that of a sphere (homaxonic), and to this form the siliceous skeleton
primarily conforms, though it may become discoid, rhabdoid, or
irregular. The nucleus is usually single, but numerous nuclei are
present in each central capsule of the Polycyttaria.

Fain. 1. SniJEitiDA, Haeck. Spherical Peripylwa with a spheri-
cal basket-work skeleton, sometimes surrounded by a spongy outer
skeleton, sometimes simple, sometimes composed of many concentric
spheres (never discoid, flattened, or irregular). The central capsule
sometimes encloses a part of the spherical skeleton, and often is
penetrated by radiating elements.

Genera (selected). Ethmosphmra, Haeck. ; Xi/ihosjJm-ra, Haeck. ;
Staurosphiera, Haeck. ; 7/r/i'<///i.Tra, Haeck. (Fig. XIV. 14) ; As-
trifinma, Haeck. ; Ilaliominn, Haeck. ; Aftinommn, Haeck. (Fig.
XIV. 17 ; note the sphere within sphere, the smallest lying in the
nucleus, and the whole series of spherical shells connected by radial
spines) ; Arai'lniw/ilm'i'it, Haeck. ; Plcrjmospheera, Haeck. ; Spunyo-
sphara, Haeck. (Fig. XVI. 8).

Fam. 2. DISCIPA, Hueck. Discoid Peripylrea ; both skeleton
and central capsule flattened.

Genera (selected). I'hteodiscns, Haeck. ; lldiodiscus, Haeck. ;
Spongodiscus, Haeck. ; Sponcjums, Haeck.

PROTOZOA

21

Fain. 3. TIIALASSICOLUDA. lYripyhea devoid of a skeleton, or
with a skeleton composed of loose siliceous spicules only. Nucleus
single ; central capsule and general protoplasm s|ilierieal.

Ccncra (selected). Thal,if:*i<vU,i, Huxley (Fig. XIII., Fig.
XIV. 1) ; Thalassospfitsra, Haeck. ; J'/ti/- nmiii'm, llaeek.

Fain. 4. POLYCYTTARIA. Peripvhea consisting of colonies of
many central capsules united by their eztracapsulai protoplasm.
Central capsules multiplying Ijy fission. Nuclei in each central
capsule numerous. Siliceous skeleton cither absent, or of loose
spicules, or having the form of a spherical fcncstrated shell sur-
rounding each central capsule.

Genera (selected). Collosphssra, Mnller (with fenestrated globular
skeleton); SjiJuerozoum, Haeck. (skeleton of numerous loose spicules
which are branched); J!:i/i!iii!ii:uitin, Hacck. (spicules simple); Col-
faouin, Miiller (devoid of skeleton, Fig. XIV. 2, 3, 4, 5).

1

each encloses a crystalline rod. c, yellow cells hing in tin- extraeapsnlar
protoplasm. 5. A small colony of Colluzott at. iu< riu<', magnified -J5

diameters. a, alveoli (vaeuolus) of tlie extraeapsular prntdjilasni ; 6,
central ea]isub s. each eontainiiiL.' besiilrs ].rotupla>Tn a hove oil-globule.
6-13. Yellow cells of various Kailiolai ia : (J, normal yellow cell; 7, 8.
division \\itb I.M ination of transverse septum ; it, a modilieil ronililiim
aeeonling to llraii'H ; in, division of a yellow cell into four ; 11, amieboid
condition of a yellow cell from the bu.ly of a dead Sphicro/.onn ; 1:2, a
similar cull in process of division ; 13, a yellow cell the protoplasm of
which is ereeping out of its cellulose envelope. 14. //'V/n..,y,/, < i -".

in, riiiii, Hacck., living example; x 400. a, nucleus; i>, central capsule ;
c, siliceous basket-work skeleton. IS. Two swarm-spore* (tla^-llnhe)

of Coltozoitiii in<'fn>i', set fl'cu trom such a central capsule as that drawn in
4 ; each contains a crystal b and a nucleus a. n;. Two swarm-spores

of Collozoum iiicrmc, of the second kind, viz., devoid of crystals, and of
two sizes, a macrospore and a microspore. They have been set free

from central capsules with c tents of a dilferent appearance from that

drawn in 4. a, nucleus. 17. Acttnomma asteracanthion, Haeck ; x 200;
one of the i'eripyloca. Entire animal in optical section, a, nucleus;
6, wall of the central capsule ; c, innermost siliceous shell enclosed iu the
nucleus; c\ middle shell lying within the central capsule ; c 2 , outer shell
lying in the extraeapsular protoplasm. Four radial siliceous spines, hold-
ing the three spherical shells together arc Been. The radial fibrillation of
the protoplasm and the fine extraeapsular pseudopodia are to be noted
18. Amphilonche M<'.(IH> H.S, Haeck; x 200; one of the Acanthometridea.
Entire animal as seen living.

ORDER 2. MONOPYL&A, Hertwig.

Characters. Silico-skeletal Kadiolaria in which the central cap-
sule is not spherical but monaxonic (cone-shaped), with a single per-
forate area (pore-plate) placed on the basal face of the cone ; the
membrane of the capsule is simple, the nucleus single ; the skeleton
is extraeapsular, and forms a scaffold-like or bee-hive-like structure
of mouaxonic form.

FIQ. XIV. Eadiolaria. 1. Central capsule of Thalamcolla nucleata,
Huxley, iu radial section, a, the large nucleus (Binnenblaschen); b,
corpuscular structures of the intracapsular protoplasm containing con-
cretions ; c, wall of the capsule (membranous shell), showing the fine
radial pore-canals ; d, nucleolar fibres (chromatiu substance) of the
nucleus. 2,3. Collozoinn i/ien/ie, J. Miiller, two dilferent forms of

colonies, of the natural size. 4. Central capsule from a colony of

Collozoum iturme, showing the intracapsular protoplasm and nucleus,
broken up into a number of spores, the germs of swarm-spores or flagellulc; ;

one of the Monopyhea.
central capsule ia
ch it is lodged.

Fam. 1. PLECTIDA, Haeck. Skeleton formed of siliceous spines
loosely conjoined.

Genera (selected). Pliiiiufimtlta, Haeck. ; Plcgmatium, Haeck.

Fam. 2. CYRTIDA, Haeck. Skeleton a monaxonic or triradiate
shell, or continuous piece (bee-hive-shaped).

Genera (selected). JL>1 hili/jilra, Haeck. ; Eueyrtidium, Haeck.
(Fig. XV.); CarpocanlttM. Haeck. (Fig. XVI. 3).

Fam. 3. BOTIUDA, Haeck. Irregular forms ; the shell composed
of several chambers agglomerated without definite order ; a single
central capsule.

Genera. Botryocyrtia, Haeck. ; Lithobotrys, Haeck.

Fam. 4. SPYKIDA, Haeck. Gcmmiuate forms, with shell con-
sisting of two conjoined chambers ; a single central capsule.

Fam. 5. STEPHIDA, Hacck. Skeleton cricoid, forming a single
siliceous ring or several conjoined rings.

Genera (selected). Acanthodesmia, Haeck.; Zygostcpkanus,
Haeck. ; Lithocirms, Haeck. (Fig. XVI. 1).

ORDERS. PHJIODARIA, Haeck. (Triinjlasa, Hertwig).
Characters. Silico-skeletal Kadiolaria iu which the central

22

PROTOZOA

Fia. XVI. Radiolaria, 1. Lithocircus annularis, Hertwig ; one of the
Monopylica. Whole animal in the living state (optical section), a, nucleus ;
6, wall of the central capsule ; c, yellow cells ; d, perforated area of the
central capsule (Monopyliea). 2. Cystidiuiu incniie, Hertwig ; one of the
Monopyltea. Living animal. An example of a Monopylaeon destitute of
skeleton, fl, nucleus ; 6, capsule-wall ; c, yellow cells in the extraeapsular
protoplasm. 3. Carjincaniuni diadema, Haeck. ; optical section of the bee-
hive-shaped shell to show the form and position of the protoplasmic body.
a, the tri-lobed nucleus ; b, the siliceous shell ; c, oil-globules ; d, the per-
forate area (pore-plate) of the central capsule. 4. Caelodendrum
gracillimum, Haeck. ; living animal, complete ; one of the Tripylrca. a, the
characteristic dark pigment (pheeodmm) surrounding the central capsule ft.
The peculiar branched siliceous skeleton, consisting of hollow fibres, and
the expanded pseudopodia are seen. 5. Central capsule of one of the
Tripytea, isolated, showing a, the nucleus ; b,c, the inner and the outer
lamina? of the capsule-wall ; d, the chief or polar aperture ; c,c, the two
secondary apertures. 6, 7. Acanthmmt rn Claimredei, Haeck. 7 shows
the animal in optical section, so as to exhibit the characteristic meeting of
the spines at the central point as in all Acanthometridea ; 6 shows the
transition from the uninuclear to the niultinnclear condition by the
breaking up of tile large nucleus, a, small nuclei ; ft, large fragments of
the single nucleus ; c, wall of the central capsule ; d, extracapsular jelly
(not protoplasm); c, peculiar intracapsular yellow cells. 8. Spongo-
spkirra streptacantlia, Haeck. ; one of the Peripylrca. .Siliceous skeleton
not quite completely drawn on the right side, a, the spherical extra-
capsular shell (compare Fig. XIV. 17), supporting very large radial spines
which are connected by a spongy network of siliceous "fibres. 9.
Aulosphxra eUgantousiTMt, Haeck.; one of the 1'hajodaria . Half of the
spherical siliceous skeleton.

capsule has a double membrane and more than one perforate area,
viz., one chief " polar aperture," and one, two, or more accessory
apertures (Fig. XVI. 5). The nucleus is single. Around the
central capsule is an abundant dark brown pigment (phieodium of
Haeckel). The siliceous skeleton exhibits various shapes regular
and irregular, but is often remarkable for the fact that it is built
up of hollow tubes.

Fam. 1. PH^EOCYSTIDA, Haeck. The siliceous skeleton is either
entirely absent or consists of hollow needles which are disposed
outside the central capsule, regularly or irregularly.

Genera (selected). Aulacantha, Haeck. ; Thalassoplancta, Haeck.

Fam. 2. PH^EOGROMIDA, Haeck. The siliceous skeleton consists
of a single fenestrated shell, which may be spherical, ovoid, or often
dipk'uric, but always has one or more large openings.

Genera (selected). Challcngeria, Wy. Thomson; Litliogromia,
Haeck.

Fam. 3. PHOSPH.ERIDA. The siliceous skeleton consists of
numerous hollow tubes which are united in a peculiar way to form,
a large spherical or polyhedral basket-work.

Genera (selected). Aulosplmra, Haeck. (Fig. XVI. 9); Aulo-
plegma, Haeck. ; C'annacantha, Haeck.

Fam. 4. PH^OCONOHIDA. The siliceous skeleton consists of two
separate fenestrated valves, similar to a mussel's shells ; often there
are attached to the valves simple or branched hollow tubes of silex.

Genera (selected). Gonchidimn, Haeck. ; Ccelodcndrum, Haeck.
(Fig. XVI. 4).

SUB-CLASS II. Acanthometridea, Lankester ( = AcantUno-skeUta).

Characters. Radiolaria in which the skeleton is composed of a
peculiar horny substance known as acauthin (rarely of silica).
The central capsule is uniformly perforate (Peripylsea type). A
divided or multiple nucleus is present in the capsule ; the capsule-
wall is single. The skeleton always has the form of spines which
radiate from a central point within the capsule where they are all
fitted to one another. Karely a fenestrated tangential skeleton is
also formed.

Fam. I. ACANTHONIDA, Haeck. Skeleton consisting of twenty
spines of acanthin disposed in five parallel zones of four spines each,
meeting one another at the central point of the organism ; nevei'
forming a fenestrated shell.

Genera (selected). AcanOiometra, J. Miiller (Fig. XVI. 6, 7) ;
Astrolonclie, Haeck. ; AmpJiilonche, Haeck. (Fig. XIV. 18).

Fam. 2. DIPLOCONIDA, Haeck. Skeleton a double cone.

Genus unieum. Diploeonus, Haeck.

Fam. 3. DORATASPIDA, Haeck. The twenty acanthin spines of
the skeleton form by transverse outgrowths a spherical fenestrated
shell.

Genera (selected). Stauraspis, Haeck. ; Dorataspis, Haeck.

Fam. 4. SPHJEROCAPSIDA, Haeek. The twenty acanthin spines
are joined together at their free apices by a simple perforate shell
of acanthin.

Genus unieum. Sph&rocapsa.

Fam. 5. LITHOLOPHIDA. Skeleton of many needles of acanthin
radiating from a single point without definite number or order.

Genera. Litholuphus, Haeck. ; Astrolophus, Haeck.

Further remarks mi the Radiolaria. It has not been possible in
the systematic summary above given to enumerate the immense
number of genera which have been distinguished by Haeckel (42) as
the result of the study of the skeletons of this group. The important
differences in the structure of the central capsule of different Radio-
laria were first shown by Hertwig, who also discovered that the spines
of the Acanthometridea consist not of silica but of an organic com-
pound. In view of this latter fact and of the peculiar numerical
and architectural features of the Acanthomctrid skeleton, it seems
proper to separate them altogether from the other Radiolaria. The
PeripyLea may be regarded as the starting point of the Radiolarian
pedigree, and have given rise on the one hand to the Acantho-
metridea, which retain the archaic structure of the central capsule
whilst developing a peculiar skeleton, and on the other hand to
the Monopyliea and Phajodaria which have modified the capsule
but retained the siliceous skeleton.

Phffiodaria.

PcripyUea.

Monopytea.

Acanthometridea.

Archi-peripyliea.
RADIOLARIA.

The occasional total absence of any siliceous or acanthiuous
skeleton docs not appear to be a matter of classiticatory importance,
since skeletal elements occur in close allies of those very few forms

PROTOZOA

23

which are totally devoid of skeleton. Similarly it does not appear
to be a matter of great significance that some forms (Polyeyttaria)
form colonies, instead of the central capsules separating from one
another after fission has occurred.

It is important to note that the skeleton of silex or acaiithin
does not correspond to the shell of other Gymnomyxa, which
appears rather to be represented by the membranous central cap-
sule. The skeleton does, however, appear to correspond to the
spiculcs of Heliozoa, and there is an undeniable affinity between
such a form as rlathrulina (Fig. VII. 2) and the Splwrid 1'eripyla-a
(such as lleliuspluera, Fig. XIV. 14). The Kadiolaria are, however,
a very strongly marked group, definitely separated from all other
Gymnoniyxa by the membranous central capsule sunk. 'in their proto-
plasm. Their differences inter sc do not affect their essential struc-
ture. The variations ill the chemical composition of the skeleton and
in the perforation of the capsule do not appear superficially. The
most obvious features in which they differ from one another relate to
tho form and complexity of the skeleton, a part of the organism so
little characteristic of the group that it may be wanting altogether.
It is not known how far the form-species and form-genera which
have been distinguished in such profusion by Haeckel as the
result of a study of the skeletons are permanent (i.e., relatively
permanent) physiological species. There is no doubt that very
many are local and conditional varieties of a single Protean species.
The same remark applies to the species discriminated among the
shell-bearing Reticularia. It must not be supposed, however, that
less importance is to be attached to the distinguishing and record-
ing of such forms because we are not able to assert that they are
permanent species.

The yellow cells (of spherical form, '005 to 0'15 of a millimetre
in diameter) which occur very generally scattered in the extra-
capsular protoplasm of Radiolaria were at one time regarded as
essential components of the Radiolarian body. Their parasitic
nature is now rendered probable by the observations of Cien-
kowski (43), Brandt (44), and Geddes (45), who have established
that each cell has a cellulose wall and a nucleus (Fig. XIV. 6 to 13),
that the protoplasm is impregnated by chlorophyll which, as in
Diatoms, is obscured by the yellow pigment, and that a starch-
like substance is present (giving the violet reaction with iodine).
Further, Cienkowski showed, not only that the yellow cells multiply
by fission during the life of the Radiolarian, but that when isolated
they continue to live ; the cellulose envelope becomes softened ;
the protoplasm exhibits amoeboid movements and escapes from the
envelope altogether (Fig. XIV. 13) and multiplies by fission.
Brandt has given the name Zooxanthdlti nutricola to the parasitic
unicellular Alga thus indicated. He and Geddes have shown that a
similar organism infests the endoderm cells of Anthozoa and of
some Siphonophora in enormous quantities, and the former has been
led, it seems erroneously, to regard the chlorophyll corpuscles of
Hi/'lra viritlis, Spongilla, and Ciliata as also parasitic Alga?, for
which he has coined the name Zoochlorella. The same arguments
which Brandt has used to justify this view as to animal chlorophyll
would warrant the creation of a genus " Phytochlorella " for the
hypothetical Alga which has hitherto been described as the
"chlorophyll corpuscles" of the cells of ordinary green plants.

Zoomnthclla nutricola does not, for some unknown reason, infest
the Acanthometridea, and it is by no means so universally present
in the bodies of the Silico-skeleta as was supposed before its
parasitic nature was recognized.

The streaming of the granules of the protoplasm has been observed
in the pseudopodia of Radiolaria as in those of Heliozoa and
Reticularia ; it has also been seen in the deeper protoplasm ; and
granules have been definitely seen to pass through the pores of the
central capsule from the intracapsular to the extracapsular pro-
toplasm. A feeble vibrating movement of the pseudopodia has
been occasionally noticed.

The proa'Ktion of swarm-spores has been observed only in
Acanthometra and in the Polycyttaria and Thalassicollidse, and
only in the two latter groups have any detailed observations been
made. Two distinct processes of swarm-spore production have
been observed by Cienkowski (43), confirmed by Hertwig (46) dis-
tinguished by the character of the resulting spores which are
called " crystalligerous " (Fig. XIV. 15) in the one case, and "di-
morphous" in the other (Fig. XIV. 16). In both processes the
nucleated protoplasm within the central capsule breaks up by a
more or less regular cell-division into small pieces, the details of
the process differing a little in the two eases. In those individuals
which produce crystalligerous swarm-spores, each spore encloses a
small crystal (Fig. XIV. 15). On the other hand, in those indi-
viduals which produce dimorphous swarm-spores, the contents of
the capsule (which in both instances are set free by its natural
rupture) are seen to consist of individuals of two sizes " macro-
spores" and "microspores," neither of which contain crystals
(Fig. XIV. 16). The further development of the spores has not
been observed in either case. Both processes have been observed
in the same species, and it is suggested that there is an alternation
of sexual and asexual generations, the crystalligerous spores

developing directly into adults, which in their turn produce in
their central capsules dimorphous swarm-spores (inaerosporcs and
mierospores), which in a manner analogous to that observed in the
Volvocinnaii Flagellata ru]ni]:ite (permanently fuse) with one
another (the larger with the smaller) before proceeding to develop.
The adults resulting fnun this process would, it is suggested, pro-
duce in their turn crystalligerous swarm-spores. Unfortunately
we have no observations to support this hypothetical scheme of a
life-history.

Fusion or conjugation of adult Radiolaria, whether preliminary
to swarni-spore-productiou or independently of it, has not been
observed this affording a distinction between them and Ilcliozoa,
and an agreement, though of a negative character, with the Reticu-
laria.

Simple fission of the central capsule of adult individuals and
subsequently of the whole protoplasmic mass has been observed in
several instances, and is probably a general method of reproduction
in the group.

The siliceous shells of the Radiolaria are found abundantly in
certain rocks. They furnish, together with Diatoms and .Sponge-
spicules, the silica which has been segregated as flint in the Chalk
formation. They are present in quantity (as much as 10 per cent.)
in the Atlantic ooze, and in the celebrated "Barbados earth" (a
Tertiary deposit) are the chief components.

GRADE B. CORTICATA, Lankester, 1878(64).

Characters. Protozoa in which the protoplasm of the cell-body,
in its adult condition, is permanently differentiated into two layers,
an outer denser cortical substance and an inner more fluid medul-
lary substance (not to be confused with the merely temporary
distinction of exoplasm and endoplasm sometimes noted in
Gymnomyxa. which is not structural but due to the gravitation and
self-attraction of the coarser granules often embedded in the
uniformly fluid protoplasm).

Since the Corticata have developed from simple Gymnomyxa
exhibiting both amceboid and flagellate phases of form and activity,
it results (1) that the forms of the body of many Corticata are
traceable to modifications of these primitive forms ; (2) that the
young stages of the Corticata are in the lower classes of that group
typical flagellulfe or amcebulrc ; and (3) that there are certain
archaic forms included in those lower classes whose position there
is doubtful, and which might be with almost equal propriety assigned
to the Gymnomyxa, since they are transitional from that lower grade
to the higher grade of Corticata.

CLASS I. SPOROZOA, Leuckart (47) ; Syn. Gregarinida, Auct.

Characters. Corticata parasitic in almost all classes and orders of
animals, imbibing nutriment from the diffusible albuminoids of
their hosts and therefore mouthless. In typical cases there is
hatched from a chlamydospore one or more modified nucleate or
non-nucleate flagcllulas (falciform young, drepanidium phase).
The flagellula increases in size and differentiates cortical and
medullary substance. Fission is common in the younger stages of
growth. The movements now become neither vibratile nor amoe-
boid but definitely restrained, and are best described as " eugle-
noid" (c/. Flagellata, Fig. XX. 27, 28). The nucleus is single,
large, and spherical. No contractile vacuole and rarely any vacuole
is present. A size of T \jth inch may be attained in this phase,
which may be definitely spoken of as the euglena phase corre-
sponding to the amreba phase of Gymnomyxa. It is usually of
oblong form, with sac-like contractile wall of cortical substance,
but may be spherical (Coceidiidea) or even amceboid (Myxosporidia).

Conjugation, followed directly or after an interval by sporulation,
may now ensue. The conjugated individuals (two), or sometimes a
single individual, become encysted. The contents of the cysts now
rapidly divide (by a process the details of which are unknown) into
minute ovoid nucleated (?) bodies ; sometimes a portion of the
protoplasm is not converted into spores but may form sporoducts
(cf. capillitium of Mycetozoa). Each piece acquires a special
cliitin-like colourless coat, and is then a chlamydospore. Rarely
one spore only is formed from the whole contents of a cyst. The
spore-coat is usually thick, and remarkable for processes and other
accessory developments. The included protoplasm of the chlamydo-
spore frequently divides into several pieces before hatching. These
usually, when set free from the spore-coat, have the form of modified
nucleated flagelluls, i.e., flagellula' in which the protoplasm is not
drawn out into a thread-like rlagellum but exhibits an elongate form,
uniformly endowed with vibratile activity. With few (if any) excep-
tions, the falciform young thus characterized penetrates a cell of some
tissue of its host and there undergoes the first stages of its growth
(hence called Cytozoa). In some forms the pre-cystic phase never
escapes from its'cell host. In other cases it remains connected with
the hospitable cell long after it has by growth exceeded by many
hundred times the bulk of its quondam entertainer ; often it loses
all connexion with its cell host and is carried away to some other
part of the infested animal before completing its growth and
encysting.

PROTOZOA

The Sporozoa are divided into four sub-classes, differing from one
another according to the form and development attained by the
euglena phase. We shall place the most highly developed first, not
only because our knowledge about it is most complete, but because
it is possible that one at least of the other sub-classes is derived by
degeneration from it.

SUB-CLASS I. Gregarinidea, Butschli (9).

Characters. Sporozoa in which the euglena phase is dominant,
being relatively of large size, elongate in form, definitely shaped,
having contractile but not viscid cortex, and exhibiting often active
nutritional and locomotor phenomena. Though usually if not
invariably cell-parasites in early youth, they become free before
attaining adult growth, and inhabit either the body-cavity or the
intestine of their hosts. Many spores are produced in the encysted
phase. The spores have an oblong, sometimes caudate coat, and
produce each one or several falciform young. At present only
known as parasites of Invertebrata.

1'jo. XVII. Sporozoa. 1, . .l/,,,,,,,-.,.,.v nil , Sb in ; 250; from the testis
of the Earthworm. Two phases of movement a ring-like contraction
passing along the body from one end to the other. 3. Individual of the

same species which has penetrated in the young stage a sperm -cell of the
Earthworm, and is now clothed as it were with spermatoblasts. 4.

Monocyitis inagna, A. Schmidt, from the testia of the Earthworm (L. tcrres-

tris, L.). Two individuals, which are implanted hy one extremity at 6 in
two epithelial cells of the rosette of the spermatic duct, a, nucleus of the
Monocystis. 5. Tailed chlamydospores of Monocystis sxmtridis,

Roll. 0. Two M. ayilis encysted, spores forming on the surface of the

protoplasm. 7. A similar cyst further advanced in spore-formation (see

Fig. XVIII.). 8. Spore of M. agilis, now elongated but still naked,
a, nucleus, x 1400. 9. The spore has now encased itself in a navicula-

shaped coat, a, nucleus. 10. The spore protoplasm has now divided

into several falciform swarm-spores, leaving a portion of the protoplasm
unused, b, Schneider's residual core. 11. Optical transverse section of
a completed spore, b, Schneider's residual core. 12. Chlamydospore

of Eluxsia c/iilonis, nov. sp., from the liver of Chiton (original.) 13,

14. Chlamydospore of Monocystis nemerlis, Koll., liberating falciform
young, b, Schneider's residue. 15. Monocystis pellucida, Kbll. (from

Nereis) ; x 150 ; to show the very thick cortical substance and its fibrilla-
tion (after Lankester, 54). 16. Monocystis sxnuridis, Kbll., two indivi-
duals adhering to one another (a syzygium). For spores see 5. 17. Mona-
cystis aphroditie, Lankester (55); x 00; remarkable among Monocystids
for its long proboscis resembling the epimerite of some Septata. 18.

Klossia lieiicinn, Aim. Schn., from the kidney of Helix Iwrtensis. A single
cell of the renul epithelium in which a full-grown Klossia is embedded.
a, nucleus of the Klossia ; a', nucleus of the renal cell. 19. Cyst of

Klossia ht'l/cina., the contents broken up into spherical chlamydo-
spores. 20. Single spore from the last, showing falciform young and a
Schneider's residue b. 21. The contents of the same spore. 22. A small
renal cell of Helix containing two of the youngest stage of Klossia. 23.
Monocystis sagittate, Lenck., from the intestine of Cajjitclla capitata ;
X 100. 24 to 31. Coeeidium oviforme, Leuck., fromtheliver of the Rabbit :
24, adult individual encysted ; 25, the protoplasm contracted a,
nucleus ; 26, 27, division into four spores, as yet naked ; 28, 29, the spores
have acquired a covering, i.e. , are chlamydospores, and each contains a single
falciform young ; 30, 31, two views of a chlamydospore more highly magni-
fied so as to show the single falciform young (from Leuckart). 32. Klossia
octopiana, Aim. Schn., from Cephalopoda, a, nucleus; b, cyst-membrane,
x 200 diam. 33. Single spherical spore of the same ; x 1400 diam ;
showing numerous falciform young, and b, Schneider's residue. 34.
M<f.ridium Lieberkuhiiii, Biitschli, one of the Myxosporidia, from the
bladder of the Pike (Esox) ; creeping euglena phase, showing strongly
lobed amoeboid character (pseudopodia and undifferentiated (?) cortex) ;
x CO diam. 35-39. Eimeriafalc/formis, Eimer sp., from the Mouse :
35, an adult non-encysted individual inhabiting an epithelial cell of the
intestine of the mouse ; 36, encysted phase ; 37, clear corpuscles appear
in the encysted protoplasm ; 38, the protoplasm now forms a single
spore containing several falciform young; b, Schneider's residue; 39,
isolated spore showing falciform young, and 6, Schneider's residue.
40. Chlamydospore of Myxobolus IHiUleri, Butschli, one of the Myxo-
sporidia from the gills of Cyprinoid Fishes, a, nucleus ; 6, refringent
corpuscle ; o, polar body or thread-capsule. 41. A similar chlamydo-
spore which has ejected the filaments from its thread capsules. 42.
Chlamydospore of a Myxosporidium infesting the kidney of Lotctmilgaris.
c, polar body (psorosperm of authors). 43, 44. Chlamydospores of
a Myxosporidium from the gills of Perca (psorosperm of authors).
Compare with the tailed chlamydospore of Monocystis sxnuridis, 5. 45
-47. Drepanidium ranarum, Lankester, the falciform young of an
unascertained Coccidiide infesting the Frog (supposed by Gaule to be pro-
duced by the blood corpuscles): 45, specimen stained by iodine ; 46, red-
blood corpuscle of Fl'Og, showing b, two contained Drepanidia, and a, the
nucleus of the blood corpuscle ; 47, living Drepanidinm. 48. Chlamy-
dospore of Lieherkuhn's Coeeidium of the Frog's kidney, perhaps belong-
ing to the life-cycle of Drepanidium ranarum.. The spore contains
two falciform young (Drepanidia?) and a Schneider's residue. 49.
Chlamydospore of Sfonocystis thatassemes, Lankester, containing nume-
rous falciform young. 50, 51. Sarcoci/stis Mie*cli>ri, Lankester: 50,
falciform young escaped from chlamydospores ; 51, adult englena phase
inhabiting a striated muscle fibre of the Pig.

OEDER 1. HAPLOCYTA, Lankester.

Characters. Gregarinidea in which there is never at any time a
partition of the medullary substance into two or more chambers.
The eugleuoid is always a single contractile sac with one mass of
medullary substance in which floats the large vesicular transparent
nucleus. Spores larger than in the next group, each producing
several falciform young.

Genus unicum. Monocystis, Stein, 1848. The various generic
subdivisions proposed by Aim. Schneider (48), and accepted by
Butschli, appear to the present writer to have insufficient characters,
and serve to complicate rather than to organize our knowledge of
the subject. We do not yet know enough of the sporulatiou and
subsequent development of the various monocystic Gregarinides to
justify the erection of distinct genera.

Monocystis ngilis, Stein, Fig. XVII. 1, 2, 3, 6, 7, 8, 9, 10, 11,
and Fig. XVIII. is the type. The other species of Monocystis
occur chiefly (and very commonly) in marine Annelids, Platyhel-
mintlics, Gephyiwa, and Tnnicata ; not in Arthropoda, Mollusca,
nor Vertebrata. The only definite differences which they present
of possibly more than specific worth, as compared with 3f. ngilis,
are in the form of the chlamydospores, which are sometimes tailed,
as in M. mrnnridis (Fig. XVII. 5), and in 31. ncmerlis (Fig. XVII.
13) and M. sipMTMStZi, and further also certain differences in the
general form, as for instance the anchor-like M. sagittata (Fig.
XVII. 231, and the prpboseidifercms .'/. iijiln;i<litx (Fig. XVII. 17).
The fine parallel striation of the cuticule in some species (M.
serjiulse, &c. ) might also be made the basis of a generic or sub-
generic group.

On the whole it seems best to leave all the species for the present
in the one genus Monocystis, pending further knowledge. It seems
probable that more than one species (at least two, .17. ngili.i and M.
niayiin) infest the common Earthworm.

OKIIEII 2. SEPTATA, Lankester.

Characters. Gregarinidea in which in the adult the medullary
substance is separated into two chambers a smaller anterior (the

PROTOZOA

protomerite) and a larger posterior (the ilputomoritc), in which lies
the nucleus. There is frequently if not always present, either in
early growth or more persistently, an anterior proboscis-like appen-
dage (the epimcrite) growing from the proti.merite. Tlie rpinn ni,
SCUTS to attach the parasite to its host, and may fur that purpose
carry booklets. It is always shed sooner or later. The phase in
which it is present is called a "cephalont," the phase after it has
broken oil' a "sporont " (see Fig. XIX. 2'2, 23). The spores are
smaller than in the preceding group, often very minute, and some-
times the cyst is complicated by the, formation of spcimdncts, and
by a kind of "capillitium " of residual protoplasm (Fig. XIX. 2).
Spores producing each only a single (?) falciform young.

Genera. Orcgarina, Dufour ; Uoplorhynchus, Yon Cams.

[The numerous genera which have been proposed at different
times by Ilammersehmidt and others, and more recently by Aime
Schneider, appear to the present writer to be unserviceable, owing
to the fact that our knowledge is as yet very incomplete. A
good basis for generic, or family distinctions might probably be
found in the greater or less elaboration of the cyst and the forma-
tion or not of sporoducts. But of the majority of Septata we do
not know the cysts or the history of sporulation ; we merely know
that some have simple cysts with complete spornlation leaving no
residue of protoplasm, and that others form cysts with double walls
and elaborate tubular ducts, whilst a part of the protoplasm is not
sporulated but forms a capillitium (Fig. XIX. 2).

Another possible basis for generic division of the Septata may
be found in the characters of the epimerite. This may be present
or absent altogether. It may exist only in the young condition or
persist until growth is completed. It may be simple, short,
elongate, or provided with booklets. The presence of booklets on
the epimerite is the only character which at present seems to serve
conveniently for generic distinction. With regard to the other
points mentioned we are not sufficiently informed, since we know
the complete history of development from the young form set free
from the spore in only one or two cases.]

The Septata are found exclusively in the alimentary canals of
Arthropoda (Insects, Myriapods, Crustacea, not Arachnida). See
Fig. XIX. for various examples of the group.

Flo. XVIII. Cyst of ilonoeystis agilis, the common Gregarinide of the
Earthworm ; x "50 diam. ; showing ripe chlamydospores and complete
absence of any residual protoplasm or other material in the cyst
(original).

SUB-CLASS II. Coccidiidea, Biitschli (9).

Sporozoa in which the euglena phase remains of relatively
minute size, of spherical shape and simple egg-cell-like structure.
It is not locomotive, but continues, until the cyst is formed, to
inhabit a single cell of the host. Many, few, or one single chlamy-
dospore are formed in the cyst. One or more falciform young
escape from each spore, and exhibit active movements (flagellula-
Hke) leading to a penetration of a tissue-cell by the young form as
in Gregarinidea. Many are parasites of Vertebrata.

OKIIER 1. MONOSPOEEA, Aim. Schn.

Characters. The whole content of the cyst forms but a single
epore.

Genus unicum. Einn'rla (in the intestinal epithelium of Triton,
Frog, Sparrow, Mouse, and the Myriapods Litliobius and Glomeris,
Fig. XVII. 35 to 39).

FIG. XIX. Sporozoa (.Septata). 1. Gregarina Uattarum, Siebold, from
the intestine of ISlatta orientalis; x 80. A syzygiltm of two individuals.
Each animal consists of a small anterior chamber, the protomerite, and a
large posterior chamber, the deutonierite, in which is the nucleus a. 2.
Over-ripe cyst of Gregarina Mattaruai, with thick gelatinous envelope e,
and projecting sporoducts d. The spores have been nearly all discharged,
but amass of them still lies in the centre of the cyst b. The specimen has
been treated with dilute KHO, and the granular contents of the cyst
dissolved. Around the central mass of spores is rendered visible the net-
work of protoplasmic origin in which the ejected spores were embedded.
This distinctly resembles in origin and function the capillitium of
Mycetozoa (Fig. III.), a, the plasmatic channels leading to the everted
sporoducts ; b, the still remaining spores ; c, the proper cyst-wall ; d, the
everted sporoducts ; e, the gelatinous envelope. 3. A ripe spore

(chlamydo spore) of Grfgarina blallarum, a long time after its escape
from the cyst; x 1600 diam. 4. Commencing encystment of a syzy-

gium of G. blatlannn. a, protomerite of one individual ; b, gelatinous
envelope ; c, protomerite of the second individual. 5. Three epithelial
cells of the mid-gut of Eliitta orientalis, into the end of each of which an
extremely young Gregarina blaltantin lias made its way. 6. Further

development of the young Gregarina ; only the epimerite a is now buried
in the substance of the epithelial cell, and this will soon break off and set the
Gregariua free. It is now a " cc]jbalont " ; it will then become a "sporont."
7. Basal part of an everted sporoduct of Gregarina blattcrinn. a, granu-
lar-fibrous mass investing the base of the duct; b, commencement of the
plasmatic channel in the interior of which the sporoduct was produced as
au invaginated cuticular formation before its eversion. 8. Gregarina

yigantea, E. Van Ben., fmm the iutestiiieof the Lobster ; x 150. a, nucleus.

26

PROTOZOA

a
o

!> Anterior end of the same more highly magnified, a, protomerite ; b, layer
of circular nbrilbe lying below'the cuticle ; c, cortical substance of the
deutomerite d, medullary substance of the deutomerite. 10. Two

spores of Gregarina mgantea (after Butschli), showing the very thick coat of
the spore. 11-15. Stayes in the development of Gregarina mgantea: 11,
recently escaped from the spore-coat, no nucleus; 12, still no nucleus,
one vibratile anil one motionless process ; 13, the two processes have
divided; one here drawn has developed a nucleus; 14, further growth;
15, the deutomerite commences to develop. 16. Cysts of Gregarina

igantea, from the rectum of the Lobster. The double contents are
jelieved by Ed. Van Beneden to be due not to conjugation previous to
encystment but to subsequent fission. 17, 18. Gregarina longicoltis,

Stein, from the intestine of Blaps nutrtitaga, : 17, cephalont phase, with a
long proboscis-like epimerite a, attached to the protomerite b ; 18,
sporont phase, the epimerite having been cast preliminarily to syzygy and
encystment. 19. Gregarina Manieri, Aim. Schneider, from the

intestine of Timarcha tenelirieosa, to show the network of anastomosing
fibres beneath the cuticle, similar to the annular fibrilUe of G. gigantea
shown in 9. 20. Gregarina (Iloylnrhynchus) obligacanthus, Stein,

from the intestine of the larva of Agrion. Cephalont witli spine-crowned
epimerite a. 21. Spores of Gregarina oligacanthus. 22, 23. Grega-

rina (Hoplorhynchus) Dujardini, Aim. Schneider, from the intestine of
Litkobius fnrticatus : 22, specimen with epimerite a, therefore a "cepha-
lont"; 23, specimen losing its epimerite by rupture and becoming a
"sporont."

ORDER 2. OLIGOSPOREA, Aim. Schn.

Characters. The cyst-content develops itself into a definite and
constant bxit small number of spores.

Genus unicum. Coccidium, Leuck. (in intestinal epithelium and
liver of Mammals, and some Invertebrates, Figs. XVII. 24 to 31).

ORDER 3. POLYSPOREA.

Characters, The cyst-content develops itself into a great num-
ber of spores (sixty or more).

Genus uuieum. Klossia, Aim. Schn. Three species of Klossia
are found in Mollusca viz., in Helix, in Cephalopoda, and in
Chiton. Schneider's genus, Adelea, from Lithobius, appears to
belong here. Kloss (49) discovered the parasite of the renal cells of
Helix hortensis represented in Fig. XVII. 18, 19, 20, 21, and 22;
Schneider that of Cephalopods, Fig. XVII. 32, 33. In Chiton Dr
Tovey has discovered a third species with very remarkable spores,
which are here figured for the first time (Fig. XVII. 12).

The Drcpnnidium Ranarum (Fig. XVII. 45, 46, 47), discovered
by Lankester (50) in the Frog's blood, is probably the falciform young
of a Coccidium parasitic in the Frog's kidney, and discovered there
by Lieberkiihn (51). A spore of this Coccidium is shown in Fig.
XVII. 48; whilst in 46 two Drepanidia which have penetrated a
red-blood corpuscle of the Frog are represented.

The Polysporous Coccidiidea come very close to the Gregarinidc
genus Mouocystis, from which they may be considered as being
derived by an arrest of development. The spores ami falciform
young of the Coceidiidea are closely similar to those of Monocystis,
and the young in both cases penetrate the tissue-cells of their host ;
but in Monocystis this is only a temporary condition, and growth
leads to the cessation of such "cell-parasitism." On the other
hand, growth is arrested in the Coccidiidea, and the organism is
permanently a cell-parasite.

Since the parasitism is more developed in the case of a cell-para-
site than in the case of a parasite which wanders in the body cavity,
it seems probable that the Coccidiidea have been derived from the
Gregarinidea rather than that the reverse process has taken place.

SUB-CLASS III. Myxosporidia, Butschli.

Characters. Sporozoa in which the euglena-phase is a large
multinucleate amceba-like organism (Fig. XVII. 34). The cysts
are imperfectly known, but appear to be simple ; some attain a
diameter of two lines. The spores are highly characteristic, having
each a thick coat which is usually provided with a bifurcate process
or may have thread capsules (like nematocysts) in its substance
(Fig. XVII. 40, 41, 42, 43, 44).

The spores contain a single nucleus, and are not known to produce
falciform young, but in one case have been seen to liberate an
amcebula. The further development is unknown. The Myxo-
sporidia are parasitic beneath the epidermis of the gills and fins, and
in the gall-bladder and urinary bladder of Fishes, both freshwater
and marine.

Genera. Myxidium, Butschli (Pike, Fig. XVII. 34); MyxoMii::,
Butschli (Cyprinoids) ; Lithocystis, Giard (the Lamellibranch Echino-
cardium).

The Myxosporidia are very imperfectly known. They present
very close affinities to the Mycetozoa, and are to be regarded as a
connecting link between the lower Gymnomyxa and the typical
Sporozoa. Possibly their large multinucleate amoeba phase is a
plasmodium formed by fusion of amrebula? set free from spores,
though it is possible that the many nuclei are the result of a division
of an original single nucleus, preparatory to spornlation.

Their spores arc more elaborate in structure than those of any
other Protozoa, and are more nearly paralleled by those of some
species of Monocystis than by those of Mycetozoa. The thread-
capsules of the spores are identical in structure with those of
Hydrozoa, and probably serve as organs of attachment, as do the
furcate processes of the spore-case. It is not certain that a definite

cyst is always or ever formed, but as occurs rarely in some" Gregari-
nidea, the spores may be formed in a non encysted amoeba form.

Although pseudopodia, sometimes short and thread-like, have been
observed in the amceba phase, yet it is also stated that a distinction
of cortical and medullary substance obtains.

The " psorosperms " of J. Miiller are the spores of Myxosporidia.

SUB-CLASS IV. Sarcocystidia, Butschli.

(This division is formed by Butschli for the reception of Sarco-
cystis, parasitic in the muscular fibres of Mammals, and of Amcebi-
diuin, parasitic in Crustacea. Both are very insufficiently known,
hut have the form of tubular protoplasmic bodies in which numer-
ous ovoid spores are formed from which falciform young escape.)

Genera. Sarcocystis, Lankester; Aincebidium, Cienkowski (52).
Sarcocystis(Fig. XVII. 50, 51, S. Micschcri, Lank. ), was first observed
by Miescher in the striated muscle-fibres of the Mouse ; then by
Rainey in a similar position in the Pig, and taken by him for the
youngest stage in the development of the cysts of Teenia solium ;
subsequently studied by Beale and others in connexion with the
cattle-plague epidemic, and erroneously supposed to have a causal
connexion with that disease. It is common in healthy butcher's
meat. See Leuckart (47).

Further remarks on the Sporozoa. The Sporozoa contrast
strongly with the large classes of Gymnomyxa, the Heliozoa,
Retieularia, and Radiolaria, as also with the Ciliate and Tentaculi-
ferous Corticata, by their abundant and rapidly recurrent forma-
tion of spores, and agree in this respect with some Proteomyxa,
with Mycetozoa, and some Flagellata. Their spores are remark-
able for the firm, chitin-like spore-coat and its varied shapes,
contrasting with the cellulose spherical spore-coat of Mycetozoa
and with the naked spores of Radiolaria and Flagellata.

The protoplasm of the more highly developed forms (Gregarini-
dea) in the euglenoid phase exhibits considerable differentiation.
Externally a distinct cuticle may be present, marked by parallel
ruga; (Monocystis serrmlx) or by fine tubercles (Monocystis sipun-
i-uli). A circlet of hooks may be formed by the cuticle at one end
of the body. Below the cuticle is sometimes developed a layer of
fibrils running transversely to the long axis of the body (Fig.
XIX. 9 and 19), which have been regarded as contractile, but are
probably cuticular. The cortical layer of protoplasm below these
cuticular structures is dense and ref'ringent and sometimes fibril-
lated (Monocystis pellurida, Fig. XVII. 15). It is the contractile
substance of the organism, and encloses the finely granular more
liquid medullary substance. The granules of the latter have been
shown by Butschli (9) to give a starch-like reaction with iodine,
&c. Probably the protoplasm in which they lie is finely reticulate
or vacuolar, and when the granules are few it is actually seen to be
so. No contractile vacuole is ever present. In Myxosporidia the
medullary protoplasm is coloured yellow by hrematoidin derived
from the blood of its host or by absorbed bile-pigment, and also
contains small crystals.

The nucleus of the Gregarinidea is a large clear capsule, with a
few or no nueleolar granules. It has never been seen in a state
of division, and it is not known what becomes of it during sporula-
tion, though sporulating Gregarinidea have been observed with
many minute nuclei scattered in their protoplasm, presumably
formed by a breaking up of the single nucleus.

The habit of attaching themselves in pairs which is common in
Gregarinidea is perhaps a reminiscence of a more extensive forma-
tion of aggregation plasmodia (compare Mycetozoa). The term
"syzygium" is applied to such a conjunction of two Gregarinidea ;
it is not accompanied by fusion of substance. The formation of
cysts is not connected with this pairing, since the latter occurs in
young individuals long before encystment. Also cysts are formed
by single Gregarinidea, as is always the case in the non-motile
Coccidiidea.

The encystment always leads to the formation of spores, but in
rare cases sporulation has been observed in unencysted Gregariui-
dea, and it occurs perhaps normally without true cyst-formation in
the Myxosporidia.

The cell-parasitism of the young Sporozoa, and their fiagellula-
like (falciform) young and active vibratile movement, are points
indicating affinity with the lower Gymnomyxa, and especially with
those Proteomyxa, such as Vampyiella and Plasmodiophora, which
are cell-parasites. Indeed it is probable that we have in this fact
of cell-parasitism, and especially of parasitism in animal cells, a
basis for the theoretical association of several unicellular organisms.
The Haplococcus of Zopf (regarded by him as a Mycetozoon) is
parasitic in the muscular cells of the Pig, and is probably related
to Sarcocystis. Recently Von Lendenfeld (53) has described in
Australia an ama-ba-like organism as parasitic in the skin of Sheep,
which will probably be found to be either a Sporozoon or referable
to those parasitic spore-producing Proteomyxa which are separated
from Sporozoa only by their negative characters (see previous
remarks on the negative characters of Proteomyxa).

The application of the name "Gregarines" has sometimes been

PROTOZOA

27

in. nl,: erroneously to external parasitic organisms, which have
nothing in common with the Sporozoa. This w;is tlie case in regard
to a fungoid growth in human hair the so-called "chignon
ilregariiK'. " Tne Silk-worm disease known as "pebrine" lias also
been attributed to a Gregarine. It seems probable that the parasitic
organism which causes that disease is (as is also the distinct parasite
causing the disease known as "flaccidezza" in the same animals)
one of the Schizomycetes (Bacteria). No disease is known at
present as due to Sporozoa, although (e.g., the A7></</ I'/iitonis)
they may lead to atrophy of the organs of the animals which they
infest, in consequence of their enormous numbers. Coccidia and
Sarcocystis are stated to occur in Man.

CLASS II. FLAGELLATA, 1 Ehrenberg.

Characters. Corticata in which the dominant phase in the life-
history is a corticate flagellula, that is. a nucleated cell-body pro-
vided with one or a few large processes of vibratile protoplasm.
Very commonly solid food particles are ingested through a distinct
cell mouth or aperture in the cortical protoplasm, though in some
an imbibition of nutritive matter by the whole surface and a nutri-
tional process chemically resembling that of plants (holophytic),
chlorophyll being present, seems to occur.

Conjugation followed by a breaking up into very numerous minute
naked spores is frequent in some ; as also a division into small
individuals (microgonidia), which is followed by their conjugation
with one another or with big individuals (macrogonidia) and subse-
quent normal growth and binary fission.

Many have a well-developed cuticle, which may form collar-like
outgrowths or stalk-like processes. Many product either gelatinous
or ehitin-like shells (cups or coanrecia), which are connected so as to
form spherical or arborescent colonies ; in these colonies the proto-
plasmic organisms themselves produce new individuals by fission,
which separate entirely from one another but are held together by
the continuity, with those already existing, of the new shells or
jelly-houses or stalk -like supports produced by the new individuals.
A single well-marked spherical nucleus, and one or more contractile
vacuoles, are always present in the full-grown form.

Often, besides ingested food-particles, the protoplasm contains
starch granules (amylon nucleus), paramylum corpuscles, chromato-
phors and chlorophyll corpuscles, some of which may be so abundant
as to obscure the nucleus. One or two pigment spots (stigmata or
so-called eye-spots) are often present at the anterior end of the body.

SUB-CLASS I. Lissoflagellata, Lankester.

Never provided with a collar-like outgrowth around the oral
pole.

ORDER 1. MONADIDEA, Biitschli.

Characters. Lissoflagellata of small or very small size and
simple structure; often naked and more or less aiiKeboid, sometimes
forming tests. Usually colourless, seldom with chromatophors.
With a single anterior large flagellum or sometimes with two
additional paraflagella. A special mouth-area is often wanting,
sometimes is present, but is never produced into a well-developed
pharynx.

Fam. 1. RHIZOMASTIGINA, Biitschli. Simple rnouthless forms
with 1 to 2 flagclla; either permanently exhibiting a Gymnomyxa-
like development of pseudopodia or capable of passing suddenly
from a firm-walled into a Gymnomyxa-like condition, when the
flagclla may remain or be drawn in. Ingestion of food by aid of
the pseudopodia.

Genera. Mrtstiyamceba, F. E. Schultze; Ciliophrys, Cienkowski
(65); Dimorpha, Gruber; Actinomonas, Kent; Trypanosoma, Gruby
(parasitic in the blood of Frogs and other Amphibia and Reptiles,
Fig. XX. 21, 22). The Rhizomastigina might all be assigned to
the Proteomyxa, with which they closely connect the group of
Flagellata. The choice of the position to be assigned to such a
form as Ciliophrys must be arbitrary.

Fam. 2. CERUOMOXADINA, Kent. Minute oblong cell-body
which posteriorly may exhibit amoeboid changes. One large
anterior flagellum. Mouth at the base of this organ. Reproduc-
tion by longitudinal fission and by multiple fission producing
spores in the encysted resting state.

Genera. Ccrcomonns, Duj. (Fig. XX. 32, 33); Hcrpetomonas, S.
Kent; Oikmnonas, Kent ( = j)/cmas, James Clark; Pscudospora,
Cienkowski, Fig. XX. 29, 3d, 31) ; Ancijrononas, S. K.

Fam. 3. CODOXCECINA, Kent. Small colourless monads similar
to Oikotnonas in structure, which secrete a fixed gelatinous or
membranous envelope or cup.

Genera. Cudonceca, James Clark; Plritythacca, Stein.

Fain. 4. BIKCECIXA, Stein. Distinguished from the last family
by the fact that the monad is fixed in its cup by a contractile
thread-like stalk ; cup usually raised on a delicate stalk.

Genera. Bicosaiai, J. Cl. ; Poteriodendron, Stein.

1 Butschli's work (9) luis been pretty closely followed in tlte diagnosis of the
groups of Flaijellata and the enumeration of genera here given.

FIG. XX. Flagellata. 1. Chlamydomonas vulciteulus, Ehr. (=Zygoselmis,
From.) ; one of the Phytomaetigoda ; free-swimming individual, a, nucleus ;
&, contractile vacuole ; c, starch corpuscle ; rf, cellulose investment ;
e, stigma (eye-spot). 2. Resting stage of the same, with fourfold

division of the cell-contents. Letters as before. 3. Breaking up of

the cell-contents into minute bithigellate swarm -spores, which escape,
and whose history is not further known. 4. Syjicrypta volvox, Ehr. ;

one of the Phytomastigoda. A colouy enclosed by a common gelatinous
test c. a, stigma; b, vacuole (non-contractile). 5. Cwfjlena volvox,

Ehr. ; one of the Monadidea. Half of a large colony, the flagellates
embedded in a conmiun jelly. 6. Chlaroyonium co'-h^n-n in, Ehr. ;

one of the Phytomastigoda. a, nucleus; 6, contractile vacuole; c, starch
grain; /, eye-spot. 7. Chlorogonium curhlorum, Ehr., one of the

Phytomastigoda. Copulation of two liberated microgonidia. a, nucleus;
b, contractile vacuole ; rf, eye-spot (so-called). S. Colony of Dinobryon

sertitla/'ia, Ehr.; x 200; one of the Monadidea. 1*. Bxmato-

coccus palustris, Girod (= Chlamydococcus, Braun, Protoeoccits Cohn),
one of the Phytomastigoda ; ordinary individual with widely separated
test, a, nucleus; b, contractile vacuole; c, amylnn nucleus (pyrenoid).
10. Dividing resting stage of the same, with eight fission products in
the common test e. 11. A microgonidium of the same. 12.

Phalansteriitjit cnn^n-intnm, Cienk., one of the Choanofiagellata ;
X 325. Disk-like o>l"iiv. 13. Eu-jlcna nVn/iX Ehr.; x 300 ; one of

the Euglenoidea. a, pigment spot (stigma) ; 6, clear space ; c, paramylum
granules ; d f chromatopnor (endocbrome plate). 14. Gvnium pectorals,
0. F. Mtiller ; one of the Phytomastigoda. Colony seen from the flat side.
X 300. a, nucleus ; b, contractile vacuole ; c, amylon nucleus. 15.

Dinobryon sertularia, Ehr. ; one of the Monadidea. a, nucleus ; b, con-

28

PROTOZOA

tractile vacuole ; c, amylon-nucleus ; rf, free colourless flagellates, probably
not belonging to Dinobryon ; e, stigma (eye-spot); /, chromatophors.
16. Peranema trichophorum, Ehr., (one ol the Euglenoidea), creeping
individual seen from the back ; x 140. a, nucleus ; b, contractile
vacuoles ; c, pharynx ; d, mouth. 17. Anterior end of Euglena acus,

Ehr., in profile, a, mouth ; b, contractile vacuoles ; c, pharynx ; rf, stigma
(eye-spot); e, paramylum-body ; /, chlorophyll corpuscles. 18. Part of

the surface of a colony of Volvox globatur, L. (Phytomastigoda), showing
the intercellular connective fthrils. a, nucleus ; b, contractile vacuole ;
c, amylura granule. 19. Two microgonidia of Volvox ylobator, L. a,

nucleus ; b, contractile vacuole. 20. Ripe asexually produced

daughter-individual of Volvox minor, Stein, still enclosed in the cyst
of the partheno-gonidium. a, young parthenp-gonidia. 21, 22.

Trypanosoma. sanguinis, Gruby ; one of the Rhizomastigina, from the
blood of Jtana esculenta. a, nucleus. x 500. 23-26. Repro-

duction of Boclo caudatus, Duj. (one of the Heteromastigoda), after Dallin-
ger and Drvsdale : 23, fusion of several individuals (plasmodium) ; 24,
encysted fusion-product dividing into four ; 25, later into eight ; 26, cyst
filled with swarm-spores. 27. Astasia tenax, O. F. Mull. (Proteus) ; one of
the Euglenoidea ; x 440. Individual with the two flagella, and strongly
contracting hinder region of the body, a, nucleus ; b, contractile vacuole,
close to the pharynx. 28. The same devoid of flagella. a, nucleus ;

c, c, the two dark pigment spots (so-called eyes) near the mouth. 29.

Oikoinonas tenno (Nonas tenno) Ehr. ; one of the Alonadidea. a, nucleus ;
b, contractile vacuole ; c, food-ingesting vacuole ; d, food-particle, x 440.
30. The food-particle d has now been ingested by the vacuole. 31.

Oikomonas mutabilis, Kent (Monadidea), with adherent stalk, a, nucleus ;
b, contractile vacuole ; c, food-particle in food vacuole. 32, 33. Cerco-
monas crassicauda, Duj. (Monadidea), showing two conditions of the
pseudopodium-protrudiug tail. a, nucleus ; b, contractile vacuoles ; c,
mouth.

Fam. 5. HETERCMONADINA, Biitschli. Small colourless or green
monads which possess, besides one chief flagelliim, one or two smaller
paraflagella attached near it, often forming colonies secreting a
common stalk.

Genera. Monas (Ehr.), Stein; Dendromonas. Stein; Cepludo-
thammum, Stein ; Anthophysa, Bory d. Vine. (Fig. XXI. 12, 13);
Dinobri/on, Ehr. (Fig. XX. 8 and 15) ; Epipyxis, Ehr. ; Uroglena,
Ehr. (Fig. XX. 5).

ORDER 2. EUGLENOIDEA, Biitschli.

Characters. Generally somewhat large and highly developed
monoflagellate forms, of mouaxonic or slightly asymmetrical
build. Cuticle present ; cortical substance firm, contractile, and
elastic ; some forms quite stiff, others capable of definite annular
contraction and worm-like elongation. At the base of the flagellum
a small or large mouth leading into a more or less distinct
pharyngeal tube. Near this is always the contractile vacuole.
Rarely a pair of flagella instead of one.

Fam. 1. CffiLOMOXADlNA. Coloured Euglenoidea, with numer-
ous small chlorophyll corpuscles or 1 to 2 large plate-like green or
brown chromatophors. Mouth and pharynx inconspicuous ; nutri-
tion probably largely vegetal (holophytic).

Genera. Ccelomonas, Stein ; Gonyostomum, Dies. ; Vacuolaria,
Cienk. ; Alicroglena, Ehr. ; Chromulina, Cienk. ; Cryptoglena, Ehr.

Fam. 2. EUGLENINA, Stein. Body monaxonic, elongated, hinder
end pointed. Spirally striated cuticle. A fine mouth-aperture
leads into the well-developed tubular pharynx. Flagellum usually
single, sometimes paired, often cast off. Near the pharynx is the
' ' reservoir " of the contractile vacuoles and several of the latter.
A single (sometimes two) stigma or colour-speck near the same
spot. Chromatophors nearly always present, generally bright
green. A large nucleus in the middle of the body. Multiplication
by longitudinal fission. Encysted condition and attendant fission
imperfectly studied. Copulation doubtful.

Genera. (a) With flexible cuticle -.EugUiM, Ehr. (Fig. XX. 13,
17; this is probably Priestley's "green matter," from which he
obtained oxygen gas ; though one of the very commonest of all
Protozoa, its life-history has yet to be worked out) ; Colacium,
Ehr. ; Eutrcptia, Perty.

(b) With stiff, shell-like cuticle : Ascoglcna, Stein ; Trachclo-
monas, Ehr. ; Lcpocinclis, Perty ; Pkacus, Nitzsch.

Fam. 3. MENOIDINA, Biitschli. Similar to the Euglenina, but
devoid of chlorophyll, a deficiency connected with the saprophytic
mode of life. Stigma always absent.

Genera. (a) With flexible cuticle : Astasiopsis, Biitschli ; Asia-
siodcs, Biitschli.

(b) With stiff cuticle and non-contractile body : Monoidium,
Perty ; Atraclotiema, Stein ; lihabdumonas, Fresenius.

Fam. 4. PERANEMINA. Very contractile (metabolic) colourless
Euglenoids. Mouth and pharynx large ; inception of solid nutri-
ment certainly observed.

Genera. Peranema, Duj. (Fig. XX. 16) ; Urccolus, Meresch.

Fam. 5. PETALOMONADINA. Colourless, non-metabolic forms.
Mouth opening at the base of the single large flagellum.

Genera. Petalomonas, Stein.

Fam. 6. ASTASINA. Colourless, metabolic, or stiff Euglenoids,
differing from the rest in having a small or large paraflagelluni in
addition to the chief one. Nutrition partly saprophytic partly
animal.

Genera. Astasia, Ehr. emend. Stein (Fig. XX. 27, 28) ; Setcro-
ncma, Duj. ; Zygoselmis, Duj. ; Sphenomuiias, Stein ; Tropido-
scyphus, Stein.

ORDER 3. HETEROMASTIGODA, Biitschli.

Characters. Small and large monads. Naked and even amo?boid
or with stiff cuticle. Two flagella at the anterior end differing in
size : the smaller directed forwards subserves the usual locomotor
function ; the larger is directed backwards and trailed, without
movement. Sometimes two backwardly directed Hagella are present.
Always a mouth and animal nutrition. Always colourless.

Fain. 1. BODONINA, Biitschli. Size of the two flagella not very
different.

Genera. Bodo, Ehb. emend. Stein (Fig. XX. 23 to 26, and Fig.
XXI. 10 ; the hooked monad and the springing monad of Dai-
linger and Drysdale (66) ; Heteromita of Dujardin and Kent);
1'hyllomitus, Stein ; Colponcma, Stein ; Dallingeria, Kent ; Tri-
mastix, Kent.

Fam. 2. ANISONEMINA, Kent. Large forms with cuticle ; differ-
ence of the two flagella considerable. Mouth, pharynx, and animal
nutrition.

Genera. Anisonana, Duj. ; Entosiphon, Stein.

ORDER 4. ISOMASTIGODA, Biitschli.

Characters. Small and middle-sized forms of monaxonic rarely
bilateral shape. Fore-end with 2, 4, or seldom 5 equal-sized and
similar flagella. Some are coloured, some colourless ; naked or
with strong cuticle or secreting an envelope. Mouth and pharynx
seldom observed ; nutrition generally holophytic (i.e., like a green
plant), but in some cases, nevertheless, holozoie (i.e., like a typical
animal).

Fam. 1. AMPHIMONADINA. Small, colourless, biflagellate Iso-
mastigoda.

Genera. Amphimonas, Duj. ( ? Pseudospora, Cienk.).

Fam. 2. SPONGOMONADINA, Stein. Small colourless oval forms
with two closely contiguous flagella. Chief character in the union
of numerous individuals in a common jelly or in branched gelatinous
tubes, the end of each of which is inhabited by a single and distinct
individual.

Genera. Spongomonas, Stein; Cladomonas, Stein; Ehipido-
monas, Stein.

[Group Phytomastigoda, Biitschli. The following three families,
viz., Chrysomonadina, Chlamydomouadina, and Volvocina, are so
closely related to one another as to warrant their union as a sub-
order. They are typical Isornastigoda, but have chlorophyll
corpuscles and holophytic nutrition with correlated deficient
mouth and pharynx, they are usually regarded. by botanists as
belonging to the unicellular Algfe.]

Fam. 3. CHRY.SOJIONADINA, Biitschli. Single or colony-forming ;
seldom an envelope. Spherical free-swimming colonies may be
formed by grouping of numerous individuals around a centre.
With two or rarely one brown or greenish brown chromatophor;
a stigma (eye-speck) at the base of the flagella.

Genera. Style/chrysalis, Stein; Chrysupyxis, Stein ; Nephrosel-
mis, Stein ; Synura, Ehr. ; Syncrypta, Ehr. (Fig. XX. 4).

Fam. 4. CHLAMYDOMONADINA. Fore-end of the body with two
or four (seldom five) flagella. Almost always green in consequence
of the presence of a very large single chromatophor. Generally a
delicate shell-like envelope of membranous consistence. 1 to 2
contractile vacuoles at the base of the flagella. Usually one eye-
sprrk. Division of the protoplasm within the envelope may pro-
duce four, eight, or more new individuals. This may occur in the
swimming or in a resting stage. Also by more continuous fission
microgonidia of various sizes are formed. Copulation is frequent.

Genera. Hymcaomonas, Stein; L'hlorawjium, Stein; C/iloro-
ffonium, Ehr. (Fig. XX. 6, 7) ; Pulyloma, Ehr. ; Chlamydomonas,
Ehr. (Fig. XX. 1, '2, 3); fftematoeoenus, Agardh ( = Chlamydo-
COCCHS, A. Braun, Stein ; Protococcus, Colin, Huxley and Martin ;
Chlamydomonas, Cienkowski); Carlcria, Diesing ; Spondylomomm,
Ehr. ; Coccomonas, Stein ; Phacotus, Perty.

Fam. 5. VOLVOCINA. Colony-building Phytomastigoda, the cell-
individuals standing in structure between Chlamydomonas and
Hsematoeoceus, and always biflagellate. The number of individuals
united to form a colony varies very much, as does the shape of the
colony. Reproduction by the continuous division of all or of only
certain individuals of the colony, resulting in the production of a
daughter colony (from each such individual). In some, probably
in all, at certain times copulation of the individuals of distinct
sexual colonies takes place, without or with a differentiation of the
colonies and of the copulating cells as male and female. The
result of the copulation is a resting zygospore (also called zygote or
oo-spermospore or fertilized egg-cell), which after a time develops
itself into one or more new colonies.

Genera. Gonium, 0. F. Muller (Fig. XX. 14) ; Stephanosph&ra,
Colin; Pandorina, Bory de Vine.; Eiulorina, Ehr. ; I'blwx,
Ehr. (Fig. XX. 18, 20).

[The sexual reproduction of the colonies of the Volvociua is one
of the most important phenomena presented by the Protozoa. In
some families of Flagelliita full-grown individuals become amoeboid,
fuse, encyst, and then break up into flagellate spores which develop

PROTOZOA

29

simply to the parental form (Fig. XX. 23 to 26). In the
Chlamydomonadina a single adult individual by division produces
small individuals, so-called "microgonidin." These copulate with
one another or with similar mierogonidia formed by other adults
(as in Chlorogonium, Fig. XX. 7) ; or more rarely in certain
genera a mierogonidium copulates with an ordinary individual
(macrogonidium). The result in either case is a " zygute, " a cell
formed by fusion of two which divides in the usual way to produce
new individuals. The microgonidium in this ease is the male
element and equivalent to a spermatozoon ; the niacrogonidiuni is
the female and equivalent to an egg-cell. The zygote is a fertilized
egg-cell, or oo-spermosporc. In the colony-building forms we find
that only certain cells produce by division mierogonidia ; and,
regarding the colony as a multicellular individual, we may consider
these cells as testis-cells and their mierogonidia as spermatozoa.
In some colony-building forms the mierogonidia copulate with
ordinary cells of the colony which, when thus fertilized, become
encysted as zygotes, and subsequently separate and develop by
division into new colonies. In Volvox the macrogonidia are also
specially-formed cells (not merely any of the ordinary vegetative
cells), so that in a sexually ripe colony we can distinguish egg-
cells as well as sperm mother-cells. Not only so, but in some
instances (Eudorina and some species of Volvox) the colonies which
produce sexual cells can not merely be distinguished from the
asexual colonies (which reproduce parthenogenetically), hut can be
distinguished also inter se into male colonies, which produce from
certain of their constituent cell-units spermatozoa or mierogonidia
only, and female colonies which produce no male cells, bnt only
macrogonidia or egg-cells which are destined to he fertilized by
the mierogonidia or spermatozoa of the male colonies.

The differentiation of the cell-units of the colony into neutral or
merely carrying cells of the general body on the one hand and
special sexual cells on the other is extremely important. It places
these cell-colonies on a level with the Euterozoa (Metazoa) in
regard to reproduction, and it cannot be doubted that the same
process of specialization of the reproductive function, at first com-
mon to all the cells of the cell-complex, has gone on in both
cases. The perishable body which carries the reproductive cells is
nevertheless essentially different in the two cases, in the Volvocina
being composed of equipollent units, in the Enterozoa being com-
posed of units distributed in two physiologically and morphologi-
cally distinct layers or tissues, the ectoderm and the endodenn.

The sexual reproduction of the Vorticellidae may be instructively
compared with that of the Phytomastigoda ; see below.]

Fam. 6. TETRAMITIXA. Symmetrical, naked, colourless, some-
what amoeboid forms, with four flagella or three and an undulating
membrane. Nutrition animal, but mouth rarely seen.

Genera. Collodidyon, Carter; Tetramitus, Perty (Fig. XXI.
11, 14 ; calycine monad of Dallingcr and Drysdale (66)) ; Monoccrco-
monaa, Grassi ; Trichomonas, Donne ; Trichomastix, Blochmann.

Fam. 7. POLYMASTIGINA. Small, colourless, symmetrical forms.
Two flagella at the hinder end of the body and two or three on each
side in front. Nutrition animal or saprophytic.

Genera. Hexamitus, Duj. (Fig. XXI. 5) ; Majastoma, Grassi ;
Polymastix, Biitschli.

Fam. 8. TREPOMONADINA, Kent. As Polymastigina, but the
lateral anterior flagella are placed far back on the sides.

Genera. Trepomonas, Duj., described recently without name by
Dallinger (67).

Fam. 9. CRTPTOMON T ADINA. Coloured or colourless, laterally
compressed, asymmetrical forms ; with two very long anterior
flagella, placed a little on one side springing from a deep atrium-
like groove or furrow (cf. Dinoflagellata and Noctiluca, to which
these forms lead).

Genera. Oyathomonas, From. ; Chilomonas, Ehr. ; Cryptomonas,
Ehr. ; Oxyrrhis, Duj.

Fam. 10. LOPHOMONADINA. A tuft of numerous flagella anteriorly.

Genus. Lophomonas, Stein (Fig. XXI. 9, connects the Flagel-
lata with the Peritrichous Ciliata).

Sub-class II. Choanoflagellata, Saville Kent.
Flagellata provided with an upstanding collar surrounding the
anterior pole of the cell from which the single flagellum springs,
identical in essential structure with the "collared cells" of Sponges.
Single or colony-building. Individuals naked (Codosit/a), orinhabit-
Ing each a cup (Salpingceca), or embedded in a gelatinous common
investment (Protcrosjxmgia).

ORDER 1. NUDA, Lankester.

Characters. Individuals naked, secreting neither a lorica (cup)
nor a gelatinous envelope.

Genera. Monosiya, S. Kent (solitary stalked or sessile) ; Codo-
siya, James Clark (united socially on a common stalk or pedicle,
Fig. XXI. 3, 4) ; Astrosiga, S. Kent ; Desmarella, S. Kent.

ORDER 2. LORICATA, Lankester.

Characters. Each individual collared-cell unit secretes a horny
cup or shell.

FIG. XXI. Flagellata. 1. Salpinyceca fustforwi*, S. Kent ; one of the
Choanoflagellata. The protoplasmic body is drawn together within the
goblet-shapeil shell, and divided into numerous spores, x 1500. 2.

Escape of the spores of the same as monoflagellate and swarm-spores.
3. Codosiga umbeliata, Tatem; one of the Choanoflagellata ; adult colony
formed by dichotomous growth ; x 625. 4. A single zooid of the same ;
x 1250. a, nucleus ; b, contractile vaeuole ; c, the characteristic "collar"
formed by cuticle on the inner face of which is a most delicate network of
naked streaming protoplasm. 5. Hcxamita injlatn, Duj, ; one of the

Isomastigoda ; x 650; normal adult; showinga, nucleus, and b, contrac-
tile vaeuole. 6, 7. Salfimja'ca itrcculata, S. Kent ; one of theCboano-
flagellata ; 6, with collar extended; 7, with collar retracted within the
stalked cup. a, nucleus; b, contractile vaeuole. 8. Polytoma nvt'lla,
Mull. sp. ; one of tbe Phytomastigoda. n, nucleus ; 6, contractile vaeuole.
X 800. 9. Lophonwnas i>lat/tiniin, Stein; one of the Isomastitroda,
from the intestine of islattn ur/V/ ( ^/V. a, nucleus. 10. Bodolens, Mull. ;
one of the Heterornastlgoda ; x 800. a, nucleus; 6, contractile vaeuole;
the wavy filament is a flagellum, the straight one is an immobile trailing
thread. 11. Tetramitus sulcatus, Stein; one of the Isomastigoda; x430.
a, nucleus ; b, contractile vaeuole. 12. Anthophysa vcgetans, O. F.
Miiller; oneof the Monaditlea; x 300. A typical, erect, shortly-branching
colony stock with four terminal monad-clusters. 13. Monad cluster of
the same in optical section (x 800), showing the relation of the
individual monads or flagellate zonids to the stem a. 14. Tetramitus
rostratus, Perty; one of the Isom&etigoda ; x 1000. a, nucleus; b, con-
tractile vaeuole. 15. Protero&pongia Haeckeli, Saville Kent ; one of
the Choanoflagellata ; x 800. A social colony of about forty flagellate
zooids. a, nucleus; b, contractile vaeuole; c, anibiciform zooid sunk

30

PROTOZOA

within the common jelly or test (compared by S. Kent to the mesoderm-
cells of a sponge-colony) ; d, similar zooid multiplying by transverse
fission ; e, normal zooids with their collars contracted ; /, hyaline mucila-
ginous common test or zoothecium ; g, individual contracted and dividing
into minute flagellate spores (microgonidia) comparable to the spermato-
zoa of a Sponge.

Genera. Salpingceca, James Clark (sedentary, Fig. XXI. 6, 7) ;
Lagenoeca, S. Kent (free swimming) ; Polyceca, S. Kent (cups united
socially to form a branching zocecium as in Dinobryon).

ORDER 3. GELATINIGERA, Lankester.

The cell-units secrete a copious gelatinous investment and form
large colonies.

Genera. P/ialanstcrium, Cienk. (Fig. XX. 12) ; Proterospongia,
Saville Kent (Fig. XXI. 15).

[The Choanoflagelhita were practically discovered by the Ameri-
can naturalist James Clark (68), who also discovered that the ciliated
chambers of Sponges are lined by collared cells of the same peculiar
structure as the individual Choanoflagellata, and hence was led to
regard the Sponges as colonies of Choanoflagellata. Saville Kent
(69) has added much to our knowledge of the group, and by his
discovery of Proterospongia (sue Fig. XXI. 15, and description)
has rendered the derivation of the Sponges from the Flagellata a
tenable hypothesis.]

Further remarks an the Flagellata. Increased attention has
been directed of late years to the Flagellata in consequence of the
researches of Cienkowski, Butsehli, James Clark, Saville Kent, and
Stein. They present a very wide range of structure, from the
simple amoeboid forms to the elaborate colonies of Volvox and
Proterospongia. By some they are regarded as the parent-group
of the whole of the Protozoa ; but, whilst not conceding to them
this position, but removing to the Proteomyxa those Flagellata
which would justify such a view, we hold it probable that they are
the ancestral group of the mouth-bearing Cortieata, and that the
Ciliata and Dinonagellata have been derived from them. One
general topic of importance in relation to them may be touched on
here, and that is the nature of the flagellum and" its movements.
Speaking roughly, a flagellum may be said to be an isolated filament
of vibratile protoplasm, whilst a cilium is one of mail}' associated
filaments of the kind. The movement, however, of a flagellum is
not the same as that of any cilium ; and the movement of all
flagella is not identical. A cilium is simply bent and straightened
alternately, its substance probably containing, side by side, a con-
tractile and an elastic fibril. A flagellum exhibits lashing move-
ments to and fro, and is thrown into serpentine waves during these
movements. But two totally distinct kinds of flagella are to be
distinguished, viz., (a) the pulsellum, and (J) the tractellum. An
example of the pulsellum is seen in the tail of a spermatozoon which
drives the body in front of it, as does the tadpole's tail. Such
a "pulsellum" is the cause of the movement of the Bacteria, It
is never found in the Flagellata. So little attention has been paid
to this fact that affinities are declared by recent writers to exist
between Bacteria and Flagellata. The flagellum of the Flagellata
is totally distinct from the pulsellum of the Bacteria. It is carried
in front of the body and draws the body after it, being used as a
man uses his arm and hand when swimming on his side. Hence
it may be distinguished as a "tractellum." Its action may be
best studied in some of the large Euglenoidea, such as Astasia.
Here it is stiff at the base and is carried rigidly in front of the
animal, hut its terminal third is reflected and exhibits in this
reflected condition swinging and undulatory movements tending to
propel the reflected part of the flagellum forward, and so exerting a
traction in that direction upon the whole animal. It is in this way
(by reflexion of its extremity) that the flagellum or tractellum of
the Flagellata also acts so as to impel food-particles against the base
of the flagellum where the oral aperture is situated.

Many of the Flagellata are parasitic (some hcematozoic, see Lewis,
70); the majority live in the midst of putrefying organic matter in
sea and fresh waters, but are not known to be active as agents of
putrefaction. Dallinger and Drysdale have shown that the spores
of Bodo and others will survive an exposure to a higher tempera-
ture than do any known Schizomyuetes (Bacteria), viz., 250 to
300 Fahr., for ten minutes, although the adults are killed at 180.

CLASS III. DINOFLAGELLATA, Butsehli.

Characters. Corticate Protozoa of a bilaterally asymmetrical form,
sometimes flattened from back to ventral surface (Diplopsalis,
Glenodiniiim), .sometimes from the front to the hinder region
(Ceratium, Peridininn, . sometimes from right to left (Dinophysis,
Amphidinium, Proroeentrum) tlie anterior region and ventral
surface being determined by the presence of a longitudinal groove
and a large flagellum "jertiug from it. In all except the genus
Proroceutrum (Fig. XXII. 6) there is as well as a longitudinal
groove a transverse groove (hence Dinifera) in which lies horizon-
tally a second (lagellum (Klebs and Butsehli), hitherto mistaken for
a girdle of cilia. The transverse groove lies either at the anterior
end of the body (Dinophysis, Fig. XXII. 3, 4 ; Amphidiiiium) or

at the middle. In Gymnodinium it takes a spiral course. In
Polykrikos (a compound metameric form) there are eight indepen-
dent transverse grooves.

The Dinoflagellata are either enclosed in a cuticular shell
(Ceratium, Peridinium, Dinophysis, Diplopsalis, Glenodinium,
Prorocentrum, &c. ) or are naked (Gymnodinium and Polykrikos).
The cuticular membrane (or shell) consists of cellulose or of a
similar substance (cf. Labyrinthulidea) and not, as has been sup-
posed, of silica, nor of chitin-like substance ; it is either a simple
cyst or perforated by pores, and may be built up of separate plates
(Fig. XXII. 10).

The cortical protoplasm contains triehocysts in Polykrikos.

The medullary protoplasm contains often chlorophyll and also
diatomin and starch or other amyloid substance. In these cases
(Ceratium, some species of Peridinium, Glenodinium, Prorocentrum,
Dinophysis acuta) nutrition appears to be holophytic. But in
others (Gymnodinium and Polykrikos) these substances are absent
and food-particles are found in the medullary protoplasm which
have been taken in from the exterior through a mouth ; in these
nutrition is holozoic. In others which are devoid of chlorophyll
and diatomin, &c., there is found a vesicle and an orilice connected
with the exterior near the base of the flngellum (cf. Flagellata) by
which water and dissolved or minutely granular food-matter is
introduced into the medullary protoplasm (Protoperidinium pellu-
cidum, Peridinium divcrgcns, Diplopsalis lenticula, Dinophysis
lie.ris). It is important to note that these divergent methods of
nutrition are exhibited by different species of one and the same
genus, and possibly by individuals of one species in successive
phases of growth (?).

No contractile vacuole has been observed in Dinoflagellata.

The nucleus is usually single and very large, and has a peculiar
labyrinthine arrangement of chromatin substance.

Transverse binary fission is the only reproductive process as yet
ascertained. It occurs either in the free condition (Fig. XXII. 2)
or in peculiar horned cysts (Fig. XXII. 8). Conjugation has been
observed iu some cases (by Stein in Gymnodinium).

Mostly marine, some freshwater. Many are phosphorescent.

The Dinoflagellata are divisible into two orders, according to the
presence or absence of the transverse groove.

ORDER 1. ADINIDA, Bergh.

Characters. Body compressed laterally ; both longitudinal and
transverse flagellum placed at the anterior pole ; a transverse groove
is wanting ; a cuticular shell is present.

Genera. Prorocentrum, Ehr. (Fig. XXII. 6, 7); Exuviella,
.( = Dinopy,iis, Stein; C'njptomonas, Ehr.).

ORDEE 2. DINIFERA, Bergh.

Characters. A transverse groove is present and usually a longi-
tudinal groove. The animals are either naked or loricate.

Fam. 1. DINOPHYIDA, Bergh. Body compressed ; the transverse
groove at the anterior pole ; the longitudinal groove present ;
longitudinal flagellum directed backwards ; loricate.

Genera. Dinophysis, Ehr. (Fig. XXII. 3, 4) ; Amphidinium,
Cl. & L. ; Ainphisolcnia, Stein; Histioneis, Stein; C itharistes,
Stein ; Ornithoccrcus, Stein.

Fam. 2. PERIDINIDA, Bergh. Body cither globular or flattened ;
transverse groove nearly equatorial ; longitudinal groove narrow or
broad ; loricate.

Genera. Protoperidinium, Bergh; Peridinium (Ehr.), Stein
(Fig. XXII. 1, 2); Protoceratium, Bergh; Ceratium, Schrank (Fig.
XXII. 15); Diplopsalis, Bergh; Glenodinium, Ehr. ; Hclcroai/isa,
Stein ; Gonyaulax, Diesiug ; Goniodama, Stein ; Blspharocysta,
Ehr. ; Podolampas, Stein ; Amphidoma, Stein ; Oxytoxum, Stein ;
Plychodiscus, Stein ; Pyrvjijtacus, Stein ; Cemtucorys, Stein.

Fam. 3. GYMNODINIDA, Bergh. As Peridinida but no lorica
(cuticular shell).

Genera. Gymnodinium (Fig. XXII. 5), Stein ; Hcmidinium,
Bergh.

Fam. 4. POLYDINIDA, Biitschli. As Gymnodinida, but with
several independent transverse grooves.

Genus. Polykrikos, Biitschli.

Further Remarks on the Dinoflayellata.1\\\s small group is at
the moment of the printing of the present article receiving a large
amount of attention from Bergh (81), Klebs (83), and Biitschli (82),
ami lias recently hern greatly extended by the discoveries of Stein
(80), the last work of the great illustrator of the Ciliate Protozoa
before his death. The constitution of the cell-wall or cuticle from
cellulose, as well as the presence of chlorophyll ami diatomin, and
the holophytic nutrition of many forms recently demonstrated by
Bergh, has' led to the suggcstiim that the Dinoflagellata are to be
regarded as plants, and allied to the Diatomacere and Desmidiaeese.
Physiological grounds of this kind have, however, as has been
pointed out above, little importance in determining the affinities
of Protozoa. Biitschli (82) in a recent very important article has
shown in confirmation of Klebs that the Diuoflagellata do not

PROTOZOA

31

possess a girdle of cilia as previously supposed, but that the struc-
ture mistaken for cilia is a second flagellum which lies horizontally
in the transverse groove. Hence the name Ciliollagellata is super-
seded by Dinoflagellata (Gr. dinos, the round area where oxen tread
out on a threshing floor).

19

FIG. XXII. Dinoflagellata and Rhynchodagellata. jv.c. In all these
figures the apparent girdle of cilia is, accodrinf; to Klebs and Butschli's
recent discovery, to be interpreted as an encircling flagellum lying in the
transverse groove. 1. Peridinium uberrimum, Allman ; x 300 (fresh-

water ponds, Dublin). Probably (according to Butschli) the processes on
the surface are not cilia nor flagellum. Both the longitudinal and the
transverse groove are well seen. 2. The same species in transverse

fission. 3. Dinophysis ovata, Cl. and L; x 350 (salt water, Norwegian

coast). 4. Dinppnysis acuininata, Cl. and L. ; X350 (salt water,

Norwegian coast). 5. Synmodinium, sp. ; xOOO. 6. Prorocen-

IniM micans, Ehr.; X300 (salt water). 7. Dorsal aspect of the

same species. 8, 9. Cysts of Peridinia; the contents of 8 divided

into eight minute naked Peridinia; X300. 10. Empty cuirass of

Cfratium divergens. Cl. and L. ; X500 ; showing the form and disposition
of its component plates. 11. The same species with the animal con-

tracted into a spherical form. The transverse groove well seen. 12.

The same species in the normal state. The apparent girdle of cilia is
really an undulating flagellum lying in the transverse groove. 13, 14.

Young stages of Noctiluca miliaris. n, nucleus; s, the so-called spine
(superficial ridge of the adult); n, the big flagellum ; the unlettered filament
(8 a flagellum which becomes the oral flagellum of the adult. 15. Cera-

tium tripm, mitt. The transverse groove well seen. The cilia really are
a single horizontal llagcllum. 10, 17. Two stages in the transverse

lission of Nootiluca miliiirix, Suriray. H, nucleus; N, fond-particles- ( tho
muscular flagellum. IS. NoetUum tnilinrix, viewed from tin: aboral

side (after Allman, Quint. ./../. Mi,: Met., Is"'.!), a, the entrance to the
atrium or Bagellar fossa (=longitudlnal grooic of liinnibgc llata); c the
superllcial ridge; il. the l.ig flagellum (=the llagellum of the transverse
groove of Dinoflagellata); li, tin- nucleus. i. The animal acted upon
by iodine solution, showing the protoplasm like the "primordial utricle"
of a vegetable cell shrunk away frum the structureless linn .sli. II or
cuirass. 20. Lateral view of Noctiluca, showing . the entrain ' f Hi.-

groove-like atrium or llagcllar fossa in which (/ is placed ; c, the superficial
ridge; rf, the big llagellum; <, the mouth and gullet, in which is seen
Krohns oral llagellum (-the chief llagellum or Hagellum of the longitu-
dinal groove of Diuo-fiagcllata) ; /, broad process of protoplasm extending
from the superllcial ridge c to the central protoplasm; ./, duplicating o(
the shell in connexion with the superlicial ridge ; /<, nucleus.

Butschli further suggests that the Dinoflagellata with their
two flagella and their i-shapcd combination of longitudinal and
transverse grooves may be derived from the Cryptomonadina (see
p. 858). In the latter a groove-like recess is present in connexion
with the origin of the two llagclla. Butschli thinks the large pro-
boscis-like Hagellum of Noctiluca (Rhynchoflagellata) represents
the horizontal flagellum of Dinoflagellata, whilst the prominent
longitudinal tlagelium of the Dinoflagellata is represented in that
animal by the small flagellum discovered by Krohn within the
gullet (see Fig. XXII. 20, c). The young form of Noctiluea (Fig.
XXII. 14) has the longitudinal flagellum still of large size.

The phosphorescence of many Dinoflagellata is a further point
of resemblance between them and Noetilnca.

Bergh has shown that there is a considerable range of form in
various species of Dinoflagellata (Ceratium, &c.), and has also drawn
attention to the curious fact that the mode of nutrition (whether
holophytic or holozoic) differs in allied species. Possibly it may be
found to differ according to the conditions of life in individuals of
one and the same species.

The drawings in Fig. XXII. were engraved before the publication
of Butschli's confirmation of Klebs's discovery as to the non-existence
of cilia in the transverse groove. The hair-like processes figured
by Allmau (91) external to the transverse groove in his Peridinium
uberrimum (Fig. XXII. 1, 2) cannot, however, be explained as a
flagellum. Biitsclili inclines to the opinion that their nature was
misinterpreted by Allman, although the latter especially calls
attention to them as cilia, and as rendering his P. ulerrimum
unlike the Peridinium of Ehrenberg, in which the cilia (horizontal
flagellum) are confined to the transverse groove.

y.B.Sfe Fig. XXVII., and explanation, p. 37.

CLASS IV. RHYNCHOFLAGELLATA. Lankester.

Characters. Corticate Protozoa of large size (^Vth inch) and
globular or lenticular form, with a firm cuticular membrane and
highly vacuolated (reticnlar) protoplasm. In Noetiluca a deep
groove is formed on one side of the spherical body, from the bottom
of which springs the thick transversely striated proboscis or
"big flagellum." Near this is the oral aperture and a cylin-
drical pharynx in which is placed the second or smaller flagellum
(corresponding to the longitudinal flagellum of Dinoflagellata).

Nutrition is holozoic. No contractile vacuole is present ; granule-
streaming is observed in the protoplasm. An alimentary tract and
anus have been erroneously described. The nucleus is spherical
and not proportionately large (see for details Fig. XXII. 18 to 20).

Reproduction by transverse fission occurs, also conjugation and,
either subsequently to that process or independently of it, a forma-
tion of spores (Cienkowsld, 87), the protoplasm gathering itself,
within the shell-likacuticnlar membrane, into a cake which divides
rapidly into numerous flagellated spores (flagellulas). These escape
and gradually develop into the adult form (Fig. XXII. 13, 14).

The proboscis-like large flagellum is transversely striated, and
exhibits energetic but not very rapid lashing movements.

Noctiluca is phosphorescent, the seat of phosphorescence being,
as determined by Allman (86), the cortical layer of protoplasm
underlying the cuticular shell or cell-wall as the primordial cuticle
of a vacuolated vegetable cell underlies the vegetable cell-wall.

Genera. Only two genera (both marine) are known : Noctiluca,
Suriray (90) (Fig. XXII. 17-20) ; Leptodiscus, Hertwig (88).

'

Further Eemarks on the EhiinrhafliiycUatit. The peculiar and
characteristic feature of Noctiluca appears to be found in its large
transversely-striated flagellum, which, according to Butschli, is not
the same as the longitudinal flagellum of the Dinoflagellata, but
probably represents the horizontal flagellum of those organisms in
a modified condition ; hence the name here proposed Rhyncho-
flagellata.

Noctiluca is further remarkable for its large size and cyst-like
form, and the reticular arrangement of its protoplasm, like that of
a vegetable cell. This is paralleled in Trachelius mum among the
Ciliata (Fig. XXIV. 14), where the same stiffening of the cuticle
allows the vacuolation of the subjacent protoplasm to take place.
The remarkable Lcptodiscus mcdusoidcs of R. Hertwig (88) appears
to be closely related to Noctiluca.

It would no doubt be not unreasonable to associate the Dino-

32

PROTOZOA

flagellata and the Rhynchoflagellata with the true Flagellata in one
class. But the peculiarities of the organization of the two former
groups is best emphasized by treating them as separate classes de-
rived from the Flagellata. Neither group leads on to the Ciliata or
to any other group, but they must be regarded as forming a lateral
branch of the family tree of "Corticata. The relationship of Nocti-
luca to Peridinium was first insisted upon by Allman, but has quite
recently been put in a new light by Biitschli, who identifies the
atrial recess of Noctiluca (Fig. XXII. 20, 6) with the longitudinal
furrow or groove of the Dinoflagellata, and the large and minute
flagella of the former with the transverse and longitudinal flagella
respectively of the latter. The superficial ridge c of Noctiluca
appears to represent the continuation of the longitudinal groove.

The phosphorescence of the sea, especially on northern coasts, is
largely caused by Noctiluca, but by no means exclusively, since
Medusre, Crustaceans, Annelids, and various Protozoa often take part
in the phenomenon. Not unfrequently, however, the phosphor-
escence on the British coasts seems to be solely due to Noetiluca,
which then occurs in millions in the littoral waters.

FIG. XXIII. Ciliata. i. Bpiroitomum ambiguum, Ehr.; one of the Hetero-
, tricha; x 120. Observe on the right side the oral groove and special hetero-

trichous band of long cilin. ft, moniliform nucleus ; b, contractile vacuole.

2. Stentor polymorphic, Miiller ; one of the Heterotricha ; x 50 ; group of

individuals with the area fringed by the heterotrichous cilia expanded
trumpet-wise. 3. Tintinnns lagenula, C. and L. ; one of the Hetero

tricha; x 300. 4. Strombidium Claparedii, S. K.; one of the Peritricha;
x 200. 5. Empty shell of Codonella campanella, Haeck.; one of the

Heterotricha ; x 180. 6, 7. Torquatella typica, Lankester. p, the supra-
oral lobe seen through the membranous collar. 8, 9. View of the
base and of the side of Trichodina pediculus, Ehr.; one of the Peritricha;
x 300. a, nucleus ; c, corneous collar ; d, mouth. 10. Sjiirochona
gemmipara, Stein ; one of the Peritricha ; x 350. a, nucleus ; g, bud. 11.
Vorticella citrina, Ehr.; x 150 (Peritricha). At d multiple fission of an
individual cell to form "microgonidia." 12. Vorticella -uricrostoma,
-Ehr. (Peritricha); x 300. At e eight "microgonidia" formed by fission
of a single normal individual. 13. Same species, binary fission, a,
elongated nucleus. 14. Vorticella nebidifira, Ehr. ; free-swimming
zooid resulting from fission in the act of detaching itself and swimming
away, possessing a posterior circlet of cilia, e, ciliated disk ; /,
pharynx. 15. Vorticella mtcrostoma, Ehr.; normal zooid with two
microgonidia (or microzooids) c,d, in the act of conjugation, o, nucleus ;
6, contractile vacuole ; e, ciliated disk ; /, pharynx. 16, Vorticella
microstoma, Ehr., with stalk contracted and body enclosed in a cyst, a,
nucleus. 17. Vorticella ncbitli/fra, Ehr. a, nucleus ; 6, contractile
vacuole ; c, 'muscular region of the body continuous with the muscle of the
stalk ; rf, pharynx (the basal continuation of the oral vestibule which
receives at a higher point the fcecal excreta and the ejected liquid from
the contractile vacuole). 18. Carchesittm spectabile, Ehr. ; retractile
colony; X 50. 19 Trichocysts of Epistylis Jlavicans, Ehr., as figured
by Greeff. 20. Opercularia stenostoma, Stein ; x 200 ; a small colony.
Observe the ciliation of the oral vestibule and the upstanding ciliate disk
(opercular-like). 21, 22. Pyzicola affinis, S. K.; one of the stalked
loricate Peritricha, in expanded and retracted states, x, the true oper-
culum. 23, 24. Gyrocoris oxyura, Stein ; one of the free-swimming
Peritricha, with spiral equatorial cilia-band ; x 250. b, contractile
vacuole. 25, 26. Ttiuricola valvata, Str. AVright ; one of the sessile
tubicolous Peritricha. Two individuals are as a result of fission tempo-
rarily occupying one tube ; tt, the valve attached to the tube, like the door
of the trap-door spider's nest and the valve of the Gasteropod Clausilium.

CLASS V. CILIATA, Ehrenherg (Infusoria seusu stricto).

Characters. Corticata of relatively large size, provided with
either a single band of cilia surrounding the anteriorly placed oral
aperture or with cilia disposed more numerously over the whole
surface of the body. The cilia are distinguished from the flagella
of Flagellata by their smaller size and simple movements of
alternate flexion and erection ; they serve always at some period of
growth as locomotor organs, and also very usually as organs for
the introduction of food particles into the mouth. Besides one
larger oblong nucleus a second (the paranucleus) is invariably (?)
present (Fig. XXV. 2), or the nucleus may be dispersed in small
fragments. Conjugation of equal-sized individuals, not resulting
in permanent fusion, is frequent. The conjugated animals separate
and their nuclei and paranuclei undergo peculiar changes ; but no
formation of spores, either at this or other periods, lias been de-
cisively observed (Fig. XXV. 8 to 15). Multiplication by transverse
fission is invariably observed in full-grown individuals (Fig. XXV.
16), and conjugation appears to take place merely as an interlude
in the fissiparous process ; consequently young or small Ciliata are
(with few exceptions) unknown. Possibly spore-formation may
hereafter be found to occur at rare intervals more generally than is
at present supposed (Fig. XXIV. 15, 18). A production of micro-
gonidia by rapid fission occurs in some Peritricha (Fig. XXIII.
11, 12, 14, 15), the liberated microgonidia conjugating with the
normal individuals, which also can conjugate with one another.

The Ciliata, with rare exceptions (parasites), possess one or more
contractile vacuoles (Fig. XXV. 3). They always possess a delicate
cuticle and a body-wall which, although constant, in form is elastic.
They may be naked and free-swimming, or they may form horny
(Fig. XXIII. 21, 25) or siliceous cup-like shells or gelatinous
envelopes, and may be stalked and form colonies like those of
Choanoflagellata, sometimes with organic connexion of the con-
stituent units of the colony by a branching muscular cord (Vorti-
cellidoe). Many are parasitic in higher animals, and of these some
are mouthless. All are holozoic in their nutrition, though some are
said to combine with this sapropliytic and holophytic nutrition.

The Ciliata are divisible into four orders according to the
distribution and character of their cilia. The lowest group (the
Peritricha) may possibly be connected through some of its members,
such as Strombidium (Fig. XXIII. 4), with the Flagellata through
such a form as Lophomonas (Fig. XXI. 9).

In the following synopsis, chiefly derived from Saville Kent's
valuable treatise (71), the characters of the families and the names
of genera are not given at length owing to the limitation of our
space.

ORDER 1. PEKITRICHA, Stein (79).

Characters. Ciliata with the cilia arranged in one anterior
circlet or in two, an anterior and a posterior ; the general surface of
the body is destitute of cilia.

Sub-order 1. NATANTIA (animals never attached).

Fam. 1. TOKQUATELLID.E.

Genns. Torquatclla, Lankester, like Slrombidium, but the^cilia
adherent so as to form a vibratile membranous collar (Fig. XXIII.
6, 7).

Fam. 2. DICTYOCYSTID.E. Animals loricate.

Fam. 3. ACTINOBOLIIXE. Illoricate, with retractile tentacula.

PROTOZOA

33

Fam. 4. HALTEium.E.

Genera. Slrombidium, Cl. & L. (Fig. XXIII. 4) ; ITaltcria,
Dujnrd., with a supplementary girdle of springing hairs ; Didinium,
Stein, (Fig. XXIV. 19).

Fam. 5. GYROCOKID/E.

Genera. Oyracoris, Stein, with an equatorial ciliary girdle spirally
disposed (Fig. XXIII. 23, 24); Uroccutrum, Nitzsch, girdle annular.

Flo. XXIV. Ciliata- 1. Ophaltnopsis sepiolse, Foett. ; a parasitic Holo-
trichous mouthless Ciliate from the liver of the Squid, a, nuclei ; b,
vacuoles (nou-contractile). 2. A similar specimen treated with picro-

carmine, showing a remarkably branched and twisted nucleus; a, in
place of several nuclei. 3. Trichonympha ay His, Leidy ; parasitic

in the intestine of the Termites (White Ants); x 600. a, nucleus; 6,
granules (food?). 4. Opalina ranarum, Purkinje ; a Holotrichrms

mouthless Ciliate parasitic in the Frog's rectum ; adult ; x 100. a, a, the
numerous regularly dispersed nuclei. 5. The same; an individual in pro-
cess of binary fission, a, nuclei. 6. The same; the process of fission has
now reduced the individuals to a relatively small size. 7. Smallest fission-
produced fragment encysted, expelled from the Frog in this state and
swallowed by Tadpoles. 8. Young uninucleate individual which has

emerged from the cyst within the Tadpole, and will now multiply its
nuclei and grow to full size before in turn undergoing retrogressive
fission. 9. Anoplophrya naidos, Duj. ; a mouthless Holotrichous

Ciliate parasitic in the worm Nais; x 200. a, the large axial nucleus; 6,
contractile vacuoles. 10. Anoplophriia prolifera, C. and L.; from the

intestine of Clitellio. Remarkable for the adhesion in a metameric series

of incomplete fission-products, a, nucleus. 11. Amphileptui gigas,

C. and L. ; oncof the Bolotricha; x 100. It, contractile vacuoles ; c, tricho-
cysts (see Fig XXIII. Ill); ''. nurlriis ; e, pharynx. 12, 13. TVoiW.,,,

nioeus, Ehr.; one of the lliiliitricha; x 75. a, nucleus; b, contra- hi.
vacuole ; c, pharynx with horny fascicular lining. 12. The fasciculate
cuticle of the pharynx isolated. 14. 2'r.7,, /,,,,. ,,/,, Ehr. (llolo-

tricha) ; x SO ; showing the reticulate arrangement of the medullary pro-
toplasm, b, contractile vacuoles; c, the cuticle-lined pharynx. IT., 10,
17, is. rcthyophthinus iimHi/ilms, Fouquet ; one of the Holotriilia;
X 120. Free individual ami successive stages of division to fonu spores.
a, nucleus; b, contractile vacuoli's. 1!. Didintum ItiUUtuan, .Miill. ;

one of the Pcritriclia ; x 200. The pharynx is everted and has seized a
Paramo2cium as food, a, nucleus; 6, contractile vacuole; c, everted
pharynx. 20. Euplotet charon, Miill.; one of the Hypotricha ; lateral

view of the animal when using its great hypotrichous processes, , as
ambulatory organs. 21. Euplotes Itarpa, Stein (Hypotricha); x 150.

h, mouth; x, hypotrichous processes (limbs). 22. Nyctotkcnu cordi-

funiiis, Stein ; a Hetei'otrichous Ciliate parasitic in the intestine of the
Frog, a, nucleus ; b, contractile vacuole ; c, food particle ; d, anus ; e,
heterotrichous band of large cilia ; /, </, mouth ; h, pharnyx ; i t small cilia.

Fam. 6. UROEOI.ARUD^E.

Genera. Trichodina, Ehr. ; two ciliate girdles ; body shaped as a
pyramid with circular sucker-like bnse, on which is a toothed corneous
ring (Fig. XXIII. 8, 9); Licnophora, Clap.; Cvdochata, Hat. JacKa.

FIG. XXV. Ciliata (conjugation, Ac.). 1. surface view of Holotrichous
Ciliate, showing the disposition of the cilia in longitudinal rows. 2.

34

PROTOZOA

Diagrammatic optical section of a Ciliate Protozoon, showing all structures
except the contractile vacuoles. a, nucleus; 6, paranucleus (so-called
nucleolus) ; c, cortical substance ; D, extremely delicate cuticle ; E,
medullary (more fluid) protoplasm ; /, cilia; (/, trichocysts ; h, filaments
ejected from the trichocysts ; i, oral aperture ; If, drop of water contain-
ing food-particles, about to sink into the medullary substance and form

lary protoplasm ; p, pharynx. 3. Outline of a Ciliate (Paramcecium), to
show the form and position of the contractile vactioles. 4-7.

Successive stages in the periodic formation of the contractile vacuoles.
The ray-like vacuoles discharge their contents into the central vacuole,
which then itself bursts to the exterior. 8-15. Diagrams of the changes

undergone by the nucleus and paranucleus of a typical Ciliate during
and immediately after conjugation : N, nucleus; jm, paranucleus; S,
condition before conjugation ; 9, conjugation effected ; both nucleus
and paranucleus in each animal elongate and become flbrillated ; 10,
two spherical paranuclei pit? in each, two dividing or divided nuclei
N 4 ; 11, the spherical paranuclei have become fusiform ; 12, there
are now four paranuclei in each (pn* and pn*), and a nucleus
broken into four or even more fragments ; 13, the two paranuclei
marked pn* in 12 have united in each animal to form the new nucleus
pn* ; the nuclear fragments are still numerous ; 14, after cessation
of conjugation the nuclear fragments N and the two unfused paranudear
pieces pn* are still present ; 15, from a part or all of the fragments
the new paranucleus is in process of formation, the new nucleus (pn 1 = N)
is large and elongated. 10. Diagram of a Ciliate in process of trans-

verse fission. 17. Condition of the nucleus N, and of the paranucleus

pn in Paramceciitm aurclia after cessation of conjugation as observed
by Biitschli. 18. Stylvnichia mytilus (one of the Hypotricha),

showing endoparasitic unicellular organisms b, formerly mistaken for
spores ; a, nuclei (after conjugation and breaking up).

Fam. 7. OPHRYOSCOLEflDJE.

Genera. Astylozoon, Engelm. ; Ophryoscolcx, Stein.

Sub-order 2. SEDENTARTA, animals always attached or sedentary
during the chief part of the life-history.

Fam. 1. VORTICELLID.E. Animals ovate, campanulate, or sub-
cylindrical ; oral aperture terminal, eccentric, associated with a
spiral fringe of adoral cilia, the right limb of which descends into
tlie oral aperture, the left limb encircling a more or less elevated
protrusible and retractile ciliary disk.

Sub-family 1. Vortieelliuse : animalcules naked.

a. Solitary forms.

Genera. Gcrda, Cl. andL. ; Scyphidia, Dujnrd. ; Spirochona, Stein
(sessile with peristome in the form of a spirally convolute mem-
branous expansion, Fig. XXIII. 10) ; Pyxidium, Kent (with a
non-retractile stalk) ; Vorticella, Linn, (with a hollow stalk in
which is a contractile muscular filament).

0. Forming dendriform colonies.

Genera. Carchcsium, Ehr. (Fig. XXIII. IS, with contractile
stalks) ; Zoothammiiim, Ehr. (contractile stalks) ; Epistylis, Ehr.
(stalk rigid) ; Opercularia, Stein (stalk rigid, ciliated disk oblique ;
an elongated peristomial collar, Fig. XX 11 1. 20).

Sub-family 2. Vaginicolirue : animalcules secreting firm cup-like
or tube-like membranous shells.

Genera. Vaginicola, Lamarck (no internal valve); Thtmcola,
Kent (with a door-like valve to the tube, Fig. XXIII. 25, 26) ;
Cothurina, Ehr. (lorica or shell pediculate ; no operculum); Pijxicola,
Kent (lorica pedunculate, animal carrying dorsally a horny oper-
culum, Fig. XXIII. 21, 22).

Sub-family 3. Ophrydina : animalcules secreting a soft gelatinous
envelope.

Genera. OpUionella, Kent; Ophrydium, Ehr.

ORDER 2. HETEROTRICHA, Stein.

Characters, A band or spiral or circlet of long cilia is
developed in relation to the mouth (the heterotrichous band)
corresponding to the adoral circlet of Peritricha ; the rest of the
body is uniformly beset with short cilia.

a. Heterotrichal band circular.

Genera (selected). Tintinnus, Schranck (Fig. XXIII. 3); Tri-
chodinopsis, Cl. and L. ; Codonella, Haeck. (with a peri-oral fringe
of lappet-like processes) ; Calccolus, Diesing.

ff. Heterotrichal band spiral.

Genera (selected). Stcntor, Oken (Fig. XXIII. 2); BUpharisma,
Perty (with an undulating membrane along the oral groove);
Spirostomum, Ehr. (oral groove linear and elongate, Fig. XXI 11.
1); Lcucophrys, Ehr. (oral groove very short).

y. Heterotrichal band in the form of a simple straight or oblique
adoral fringe of long cilia.

Genera (selected). Bursaria, Mtiller ; Nyctothcrus, Leidy (with
well-developed alimentary tract and anus, Fig. XXIV. 22) ; Jlalan-
tidium, Cl. and L. (V. culi parasitic in the human intestine).

ORDER 3. HOLOTRICHA, Stein.

Characters. There is no special adoral fringe of larger cilia, nor
a band-like arrangement of cilia upon any part of the body ; short
cilia of nearly equal size are uniformly disposed all over the surface.
The adoral cilia sometimes a little longer than the rest.

o. With no membraniform expansion of the body wall.

Genera. Paramcecium, Ehr. (Fig. XXV. 1, 2) ; Prorodon, Ehr.

(Fig. XXIV. 13); Coleps, Ehr. ; Enchclys, Ehr. ; Trachelocerea, Ehr. ;
Tracliclius, Ehr.; Amphileptus, Ehr.; Ictiiyopkthirius, Fouquet
(Fig. XXIV. 15).

. Body with a projecting membrane, often vibratile.

Genera. Ophryoglena, Ehr.; Colpidium, Stein; Lcmbus, Cohn ;
Trichonympha, Leidy (an exceptionally modified form, parasitic,
Fig. XXIV. 3).

7. Isolated parasitic forms, devoid of a mouth.

Genera. Opalina, Purkinje (nuclei numerous, no contractile
vacuole, Fig. XXIV. 4 to 8) ; Bcnedcnia, Foett. ; Opalinopsis,
Foett. (Fig. XXIV. 1, 2); Anoplophrya, Stein (large axial nucleus,
numerous contractile vacuoles in two linear series, Fig. XXIV. 9
10) ; Haptophrya, Stein ; Hoplitoplmja, Stein.

OKDEE 4. HYPOTK1CHA, Stein.

Characters. Ciliata in which the body is flattened and the
locomotive cilia are confined to the ventral surface, and are often
modified and enlarged to the condition of muscular appendages
(seta; so-called). Usually an adoral baud of cilia, like that of
Heterotricha. Dorsal surface smooth or provided with tactile
hairs only. Mouth and anus conspicuously developed.

a. Cilia of the ventral surface uniform, fine, and vibratile.

Genera. Chilodon, Ehr. ; Loxodcs, Ehr. ; Dystcria, Huxl. ;
Ifuxlcya, Cl. and L.

j3. Cilia of the ventral surface variously modified as- setae
(muscular appendages), styles, or uncini.

Genera. <S7j/Zo)uc7n', Ehr. (Fig. XXV. 18); Oxytricha, Ehr.;
Euplotes, Ehr. (Fig. XXIV. 20, 21).

Further remarks on the Ciliata. The Ciliata have recently
formed the subject of an exhaustive treatise by Mr Saville Kent (71)
which is accessible to English readers. On the other hand Prof.
Biitschli has not yet dealt with them in his admirable critical
treatise on the Protozoa. Hence a large space has not been devoted
in this article to the systematic classification and enumeration of
their genera. See (79) and (93).

One of the most interesting features presented by the group is
the presence in many of a cell anus as well as a cell mouth (Fig.
XXIV. 22, d). In those devoid of an anus the undigested
remnants of food are expelled either by a temporary aperture on
the body-surface or by one opening into the base of the pharynx.
In many parasitic Ciliata, as in higher animal parasites, such as
the Cestoid worms, a mouth is dispensed with, nutriment being
taken by general imbibition and not in the solid form. Many
Ciliata develop chlorophyll corpuscles of definite biconcave shape,
and presumably have so'far a capacity for vegetal nutrition. In
Vorticella viridis the chlorophyll is uniformly diffused in the pro-
toplasm and is not in the form of corpuscles (72).

The formation of tubes or shells and in connexion therewith of
colonies is common among the Peritricha and Heterotricha. The
cuticle may give rise to structures of some solidity in the form of
hooks or tooth-like processes, or as a lining to the pharynx (Fig.
XXIV. 12).

The phenomena connected with conjugation and reproduction
are very remarkable, and have given rise to numerous misconcep-
tions. They are not yet sufficiently understood. It cannot be
surely asserted that any Ciliate is at the present time known to
break up, after encystment or otherwise, into a number of spores,
although this was at one time supposed to be the rule. Icthyoph-
thirius (Fig. XXIV. 15 to 18) and some Vorticellre (76) have been
stated, even recently, to present this phenomenon ; but it is not
impossible that the observations are defective. The only approach
to a rapid breaking up into spores is the multiple formation (eight)
of microgonidia or microzooids in Vortieellidte (Fig. XXIII. 11,
12); otherwise the result of the most recent observations appears to
lie that the Ciliata multiply only by binary fission, which is very
frequent among them (longitudinal in the Peritricha, transverse
to the long axis in the others).

Several cases of supposed formation of spores within an adult
Ciliate and of the production eiidogeuously of numerous "acineti-
form young " have been shown to be cases of parasitism, minute
unicellular parasites, c.y., parasitic Arineta' (such as Sphierophrya
described and figured in Fig. XXVI.) being mistaken for the young.

The phenomenon of conjugation is frequent in the Ciliata, and is
either temporary, followed by a separation of the fused individuals,
as in most cases, or permanent, as in the case of the fertilization
of normal individuals by the microgonidia of Vorticellidre.

Since the process of conjugation or copulation is not followed
by a formation of spores, it is supposed to have merely a fertilizing
effect on the temporarily conjoined individuals, which nourish
themselves and multiply by binary fission more actively after the
prut-ess than 1'cl'ure (In-nee termed "rejuvenescence)."

Remarkable changes have been from time to time observed in
the nuclei of Ciliata during m- subsequently to conjugation, and
these were erroneously interpreted by Balbiani (73) as indicating
the formation of spennatozoa and ova. The nuclei exhibit at one
period great elongation and a distinct fibrillation, as in the dividing

PROTOZOA

35

nuclei of tissue cells (compare Fig. I. and Fig. XXV. 9, 11, 17).
The tibrilhe were supposed to lie apermatozoids, and this erroneous
view was confirmed by the observation of rod-like Bacteria
(Schizomycetes) which in some instances infest the deeper proto-
plasm of large L'iliata.

The true history of the changes which occur in the nuclei of
conjugating Ciliata has been determined by Butschli (74) in some
typir.'il instances, but the matter is by no means completely under-
stood. The phenomena present very great obstacles to satis-
factory examination on account of their not recurring very fre-
quently and passing very rapidly from one phase to another.
They have not been closely observed in a sufficiently varied
number of genera to warrant a secure generalization. The follow-
ing scheme of the changes passed through by the nuclei must be
regarded as necessarily referring to only a few of the larger
Heterotricha, Holotricha, and Hypotricha, and is only probably
true in so far as details are concerned, even for them. It is at
the same time certain that some such series of changes occurs in
all Ciliata as the sequence of conjugation.

In most of the Ciliata by the side of the large oblong nucleus is a
second smaller body (or even two such bodies) which has been very
objectionably termed the nucleolus (Fig. XXV. 8), but is better
called the " parauucleus " since it has nothing to do with the nucle-
olus of a typical tissue-cell. When conjugation occurs and a
"syzygium" is formed, both nucleus and paranucleus in each con-
jugated animal elongate and show fibrillar structure (Fig. XXV.
10). Each nucleus and paranncleus now divides into two, so that
we get two nuclei and two paranuclei in each animal. Elongation
and fibrillation are then exhibited by each of these new elements
and subsequently fission, so that we get four nuclei and four para-
nuclei in each animal (11, 12). The fragments of the original
nucleus (marked N in the figures) now become more dispersed and
broken into further irregular fragments. Possibly some of them
are ejected (so-called " cell excrement "); possibly some pass over
from one animal to the other. Two of the pieces of the four-times-
divided paranucleus now reunite (Fig. XXV. 13), and form a
largish body which is the new nucleus. The remaining fragments
of paranucleus and the broken down nucleus now gradually dis-
appear, and probably as a remnant of them we get finally a few cor-
puscles which unite to form the new paranucleus (14, 15). The
conjugated animals which have separated from one another before
the later stages of this process are thus reconstituted as normal
Ciliata, each with its nucleus and paranucleus. They take food
and divide by binary fission until a new period of conjugation
arrives, when the same history is supposed to recur.

The significance of the phenomena is entirely obscure. It is not
known why there should be a paranucleus or what it may correspond
to in other cells whether it is to be regarded simply as a second
nucleus or as a structurally and locally differentiated part of an
ordinary cell-nucleus, the nucleus and the paranucleus together
being the complete equivalent of such an ordinary nucleus. An
attempt has been made to draw a parallel between this process and
the essential features of the process of fertilization (fusion of the
spermatic and ovicell nuclei) in higher animals ; but it is the fact
that concerning neither of the phenomena compared have we as yet
sufficiently detailed knowledge to enable us to judge conclusively as
to how far any comparison is possible. Whilst there is no doubt
as to the temporary fusion and admixture of the protoplasm of the
conjugating Ciliata, it does not appear to be established that there
is any transference of nuclear or paranuclear matter from one indi-
vidual to the other in the form of solid formed particles.

Conjugation resulting merely in rejuvenescence and ordinary fis-
sive activity is observed in many Flagellata as well as in the Ciliata.

A noteworthy variation of the process of binary fission occurring
in the parasite Opalina deserves distinct notice here, since it is inter-
mediate in character between ordinary binary fission and that
multiple fission which so commonly in Protozoa is known as spore-
formation. In Opalina (Fig. XXIV. 4) the nucleus divides as the
animal grows ; and we find a great number of regularly disposed
separate nuclei in its protoplasm. (The nuclei of many other
Ciliata have recently been shown to exhibit extraordinary branched
and even "fragmented "forms; compare Fig. XXIV. 2.) At a certain
stage of growth binary fission of the whole animal sets in, and growth
ceases. Consequently the products of fission become smaller and
smaller (Fig. XXIV. 6). At last the fragments contain each but
two, three, or four nuclei. Each fragment now becomes encased
in a spherical cyst (Fig. XXIV. 7). If this process had occurred
rapidly, we should have had a uninucleate Opalina breaking up
at once into fragments (as a Gregarina does), each fragment being
a spore and enclosing itself in a spore-case. The Opalina ranarum
lives in the rectum of the Frog, and the encysted spores are
formed in the early part of the year. They pass out into the
water and undergo no change unless swallowed by a Tadpole, in
the intestine of which they forthwith develop. From each spore-
case escapes a uninucleate embryo (Fig. XXIV. 8), which absorbs
nourishment and grows. As it grows its nucleus divides, and so
the large multinucleate form from which we started is reattained.

This history has important bearings, not only on the nature of
sporulatiou, but also on the question of the significance of the
multinucleate condition of cells. Here it would seem that the
formation of many nuclei is merely an anticipation of the retarded
fissive process.

It is questionable how far we are justified in closely associating
Opalina, in view of its peculiar nuclei, with the other Ciliata. It
seems certain that the worm-parasites sometimes called Opalinre, but
more correctly Anaplophrya, &c., have no special affinity with the
true Opalina. They not only differ from it in having one large
nucleus, but in having numerous very active contractile racuoles
(75).

Recently it has been shown, more especially by Gruber (84), that
many Ciliata are multinucleate, and do not possess merely a single
nucleus and a paranucleus. In Oxytricha the nuclei are large and
numerous (about forty), scattered through the protoplasm, whilst
in other cases the nucleus is so finely divided as to appear like a
powder or dust diffused uniformly through the medullary proto-
plasm (Trachelocerca, Choenia). Carmine staining, after treatment
with absolute alcohol, has led to this remarkable discovery. The
condition described by Foettinger (85) in his Opalinopsis (Fig.
XXIV. 1, 2) is an example of this pulverization of the nucleus. The
condition of pulverization had led in some cases to a total failure
to detect any nucleus in the living animal, and it was only by the
use of reagents that the actual state of the case was revealed.
Curiously enough, the pulverized nucleus appears periodically to
form itself by a union of the scattered particles into one solid
nucleus just before binary fission of the animal takes place ; and
on the completion of fission the nuclei in the two new individuals
break up into little fragments as before. The significance of this
observation in relation to the explanation of the proceedings of the
nuclei during conjugation cannot be overlooked. It also leads to
the suggestion that the animal cell may at one time in the history
of evolution have possessed not a single solid nucleus but a finely
molecular powder of chromatin-substance scattered uniformly
through its protoplasm, as we find actually in the living Trachelo-
cerca.

Some of the Ciliata (notably the common Vorticella;) have been
observed to enclose themselves in cysts ; but it does not appear that
these are anything more than " hypnocysts " from which the animal
emerges unchanged after a period of drought or deficiency of food.
At the same time there are observations which seem to indicate that
in some instances a process of spore-formation may occur within
such cysts (76).

The differentiation of the protoplasm into cortical and medul-
lary substance is very strongly marked in the larger Ciliata.
The food-particle is carried down the gullet by ciliary currents
and is forced together with an adherent drop of water into the
medullary protoplasm. Here a slow rotation of the successively
formed food-vacuoles is observed (Fig. XXV. 2, I, m, n, o), the
water being gradually removed as the vacuole advances in position.
It was the presence of numerous successively formed vacuoles which
led Ehrenberg to apply to the Ciliata the not altogether inappro-
priate name " Polygastrica. " The chemistry of the digestive pro-
cess has not been successfully studied, but A. G. Bourne (8) has
shown that, when particles stained with water-soluble aniliu blue
are introduced as food into a Vorticella, the colouring matter is
rapidly excreted by the contractile vacuole in a somewhat concen-
trated condition.

The differentiation of the protoplasm of Ciliata in some special
cases as "muscular" fibre cannot be denied. The contractile
filament in the stalk of Vorticella is a muscular fibre and not
simple undifferentiated contractile protoplasm ; that is to say, its
change of dimensions is definite and recurrent, and is not rhythmic,
as is the flexion of a cilium. (Perhaps in ultimate analysis it is
impossible to draw a sharp line between the contraction of one side
of a cilium which causes its flexion and the rhythmical contraction
of some muscular fibres. ) The movements of the so-called " setae "
of the Hypotricha are also entitled to be called "muscular," as
are also the general contractile movements of the cortical substance
of large Ciliata. Haeckel (77) has endeavoured to distinguish
various layers in the cortical substance; but, whilst admitting that,
as in the Gregarinre, there is sometimes a distinct fibrillation of
parts of this layer, we cannot assent to the general distinction of a
" myophane" layer as a component of the cortical substance.

Beneath the very delicate cuticle which, as a mere superficial
pellicle of extreme tenuity, appears to exist in all Ciliata we
frequently find a layer of minute oval sacs which contain a spiral
thread ; the threads are everted from the sacs when irritant
reagents are applied to the animal (Fig. XXV. 2, g, h). These
were discovered by Allman (78), and by him were termed " tricho-
cysts." They appear to be identical in structure and mode of
formation with the nematocysts of the Ccelentera and Platyhelmia.
Similar trichocysts (two only in number) are found in the spores
of the Myxosporidia (see ante, page 855).

The comparative forms of the nucleus and of the contractile
vacuoles, as well as of the general body-form, &c., of Ciliata may

36

PROTOZOA

be learnt from an examination of Figs. XXIII., XXIV., XXV.,

and the explanations appended to them.

CLASS VI. ACINETARIA, Lankester (Tentaculifera, Huxley).

Characters. Highly specialized Corticate Protozoa, probably
derived from Ciliata, since their young forms are provided with a
more or less complete investment of cilia. They are distinguished
by having no vibratile processes on the surface of the body iu the
adult condition, whilst they have few or many delicate but firm

Fro. XXVI. Acinetaria. 1. Rhynclieta cydopum, Zenker. a, nucleus;
6, contractile vacuole ; only a single tentiicle, ami that suctorial ; x 150.
Parasitic on Cyclops. 2. Sphterophrya uroxttjlm, Maupas ; normal

adult; x 200. a. nucleus ; 6, contractile vacuole. Parasitic in ri.istyhi.
3. The same dividing by transverse fission, the anterior moiety with tem-
porarily developed t-ilia. , nucleus; b, contractile vacuole. 4, 5, 6.
Spharophrya xti'iit'irea, Maupas; x 200. Parasitic in Stentor, and at one
time mistaken for its young. 7. Trichnphrya epistylidis, Cl. and L. ;
x 150. ft, nucleus; b, contractile vacimlr. 8. ffemiovhrya <j>'i/iuii-
para, Hertwig; x 400. Example with six buds, into each of which a
branch of the nucleus a is extended. 9. Tile same species, showing
the two kinds of tentacles (the suctorial ami the pointed), and the con-
tniL'tile vacuoles l>. 10. Cilmted embryo of Podnpl/rya Sleinii, ('1. and
L.; x 300. 11. Arini'tii iiriiinlia, Saville Kent; X 100 ; showing pedun-
culated lorica, ami animal with two hunches of entirely suctorial tentacles.
a, nucleus. 12. Sphurophrya mayna, Maupas ; x 300. It has seized

with its tentacles, and is in the act of sucking out the juices of six examples
of the ciliate Cvlpoda paruifrons. 13. Podophrya elongata, Cl. and L. ;

x 150. a, nucleus; b, contractile vacuole. 14. Hemiophrya Benedenii,
Fraip.; x 200; the suctorial tentacles retracted. 15. Vendrocometes

paradoxus, Stein; x 350. Parasitic on Gammarus pulcx. a, nucleus;
b, contractile vacuole ; c, captured prey. 16. A single tentacle of

Podophrya; x 800. (Saville Kent.) 17-20. Dendrosoma radians, Ehr. :
17, free-swimming ciliated embryo, X 600 ; 18, earliest fixed condition of
the embryo, x 600 ; 19, later stage, a single tentaculiferous process now
developed, X 600; 20, adult colony; c, enclosed ciliated embryos ; d,
branching stolon ; e, more minute reproductive (!) bodies. 21. Ophryo-
dendron pedicellatum, Hincks ; x 300.

tentacle-like processes, which are either simply adhesive or tubular
and suctorial. In the latter case they are provided at their ex-
tremity with a sucker-disk and have contractile walls, whereas in
the former case they have more or less pointed extremities. The
Acinetaria are sedentary in habit, even if not, as is usual, per-
manently fixed by a stalk. The nucleus is frequently arboriform.
Reproduction is effected by simple binary fission, and by a modified
fission (bud-fission) by which (as in Reticularia and Arcella) a
number of small bud-like warts containing a portion of the branched
parental nucleus are nipped off from the parent, often simul-
taneously (Fig. XXVI. 8). These do not become altogether dis-
tinct, but are for a time enclosed by the parental cell each in a
sort of vacuole or brood-chamber, where the young Acinetarian
develops a coat or band of cilia and then escapes from the body of
its parent (Fig. XXVI. 10, 17). After a brief locomotive existence,
it becomes sedentary, develops its tentacles, and loses its cilia.

The Acinetaria have one or more contractile vacuoles. Their
nutrition is holozoic.

The surface of the body in some crises is covered only by a
delicate cuticle, but in other cases a definite membranous shell or cup
(often stalked) is produced. Freshwater and marine. See Fraipont
(89).

ORDER 1. SUCTORIA, Kent.

A greater or less proportion or often all of the tentacles are
suctorial and terminated with sucker-like expansions.

Genera. Ehyncheta, Zenker (stalkless, naked, with only one
tentacle ; epizoic on Cyclops ; Fig. XXVI. 1) ; Urnula, C. and L. ;
Sphszrophrya, C. and L. (naked, spherical, with distinctly capitate
tentacles only ; never with a pedicle ; parasitic within Ciliata,
supposed young ; Fig. XXVI. 2-6, 12) ; Trichophrya, C. and L. (as
Sphxrophrya, but oblong and temporarily fixed without a pedicle);
Podophryn, Ehr. (naked, solitary, globose, ovate or elongate, fixed
by a pedicle ; tentacles all suctorial, united in fascicles or distri-
buted irregularly; Fig. XXVI. 10, 13, 16) ; Hemiophrya, S. Kent (as
Podophrya, but the tentacles are of the two kinds indicated in the
definition of the group ; Fig. XXVI. 8, 9, 14); Podocyathus, S. Kent
(secreting and inhabiting stalked membranous cups or loricse ; ten-
tacles of the two kinds) ; Solcnophrya, C. and L. (with a sessile
lorica ; tentacles only suctorial) ; Acineta, Ehr. (as Solcnophrya,
but the lorica is supported on a pedicle; Fig. XXVI. 11); Dendro-
cometcs, Stein (cuticle indurated ; solitary, sessile, discoid ; tentacles
peculiar, viz., not contractile, more or less branched, root-like, and
perforated at the extremities and suctorial in function ; Fig.
XXVI. 15). Dendrosoma, Ehr. (forming colonies of intimate!)'
fused individuals, with a basal adherent protoplasmic stolon and
upstanding branches the termination of which bear numerous capi-
tate suctorial tentacles only ; Fig. XXVI. 17-20).

ORDERS. NON-SUCTORIA, Lankester (*= Actinaria, Kent).

Characters. Tentacles filiform, prehensile, not provided with a
sucker.

Genera. Ephdota, Str. Wright (solitary, naked, pedunculate,
with many flexible inversible tentacles) ; Adinocyathus, S. Kent ;
Ophryodcndron, C. and L. (sessile, with a long, extensile, anterior
proboscis bearing numerous flexible tentacles at its distal extremity ;
Fig. XXVI. 21) ; Acinctopsis, Robin (ovate, solitary, secreting a
stalked lorica ; from the anterior extremity of the animal is deve-
loped a proboscis-like organ which does not bear tentacles).

Further remarks on the Acinetaria, The independence of the
Acinetaria was threatened some years ago by the erroneous view of
Stein (79) that they were phases in the life-history of VorticelHdae.
Small parasitic forms (Sphserophrya) were also until recently
regarded erroneously as the " aciuetiform young " of Ciliata.

They now must be regarded as an extreme modification of the
Protozoon series, in which the differentiation of organs in a
unicellular animal reaches its highest point. The sucker-tentacles
of the Suctoria are very elaborately constructed organs (see Fig.
XXVI. 16). They are efficient means of seizing and extracting the
juices of another Protozoon which serves as food to the Acinetarian.
The structure of Dendrosoma is remarkable on account of its
multieellular character and the elaborate differentiation of the
reproductive bodies.

The dilation of the embryos or young forms developed from the
buds of Acinetaria is an indication of their ancestral connexion
with the Ciliata. The cilia are differently disposed on the young
of the various genera (see Fig. XXVI. 10, 17).

PROTOZOA

37

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Lcipsic, 1R76. (47) LEFCKAPT (Spornznn), Die mrnxchlichcn Paraxiten, 2d ed. t
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p. 515, ls;r,, p. l:;-j ami p. 41CI, Ihsl, p. :;s7. (49) KUMB(Coccidiiik- of Helix),
A?>!i<i>t>i. >i. jS'-vjX 1 . ni>< r<j. n-iturf. (jfSfltxi'h., 1., ISijii. (50) LANKESTKIC, E. UAV
(Drepanidhun), Quart. JOUT. 2tffcr. .S-/., vol. xxii., 1S8L', p. 5a. (51) Lir;iiEi:KUHN
(Coccidlam of ITO^'S ki'liu-y), Archiv /. Annt. and J'hysioloy., 18J4. (52)
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LENDENKBLD (parasitic aimcboid oi^unisin). in i'r<><-<-lin<j* of Linnean Xociely of
New South Wales, 1885. (54) LANKKSTER, E. RAY (Alanocystis pelfucida), Quart.
Jour. Aficr. Sci. (IR-W series), vol. vi., isiifi. (55) LANKISTER, E. RAY (Mono-
cyst is aphroditie), Quart. Jour. Aficr. AVi. (new series), vol. iii., 1863. (56)
HEICTWIO, R. (Aphrothoi'aca), in (trintniiinii* dfr Radiolarien, Jtna, 1879. (57)
ARCHER (Chlareydophora), " Ke'sunn'. iVc.," (^nart. Jour. Ahcr. Sci., vol. xvi.,
1876. (58) HERTWIG, It., und LESSEE (Chalarothoraca), Archiv/. Mikrosk. Anat. t
x., Supplement, 1874. (59) LANKKSTER, E. KAY (Haliphysema), Quart. Jour.
Aficr, Sci. (new series), vol. xix., 187'J. (60) HAKCKKL (I'liysemaria), Jt-naischc
Zfitschr., x. (61) BESSELS (Astrnrhiza), J<:nni$fhc Z> ttschr., ix. (62) CARPENTER
(classification of Reticularia), "Researches on the Fovaminifera," Phil. Trans.,
185(i-59-(iO. (63) HAECKEI, (Hadiolaria), JJie liadw/arien, Berlin, 1862. (64)
LANKESTER, E. RAY (term Corticata), Preface to the English edition of Gegenbaur's
Elements of Comparative Anatomy, 1878. (65) CIENKOWSKI (Ciliophrys), Archie
f. Afikrosk. Anat., xii., 1876, p. 15-50. (66) DALUNGER and DRYSDALE (hooked
and springing Monads), a serk-s of papers in the Monthly Aficroscopical Journal,
1873-74-75. (67) IULLIXGKR (Trcpomonas), President's Address, Jour, of the
Hoy. Aficr. Soc., April 1885. (68) JAMES CLARK (Choanoflagellata, Alemoirs of
the Boston Society of A'at. Hist., 18U7, vol. i. (69) SAVILLE KENT (Choano-
flagellata), Monthly Aficroscopical Journal, vol. vi., 1871. (70) LEWIS, T. R.
(Hrematoznic Flagellatu), Quart. Jour. Alicr. S<'i., vol. xxiv., 1884, and vol. xix.,
1879. (71) SAVILLE KENT, Manual of the Jnfusoria, London, 1882. (72)
SALLITT, J. (chlorophyll of Ciliata), Quai t. Jour. Alicr . Sci. t 1884. (73) BALBIANI
(sexuality of Ciliata), Journal de la Physiologic, i., iii., and iv., and Archives de
Zool. Experim.i ii., 1873. (74) BUTSCHLI (conjugation of Ciliata), Abhand. d.
Senkenberg. naturf. Gesetlschaft., x., 1876. (75) LANKESTER (Opalina=Anaplo-
phyra), Quart. Jcur. Aficr. Sci. (new series), vol. x., 1870. (76) ALLMAN (encysted
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HAECKEL (structure of CiJiata), Zur Morphologic der hifusorien, Leipsic, 187-t.
(73) ALLMAN (trichocysts of Ciliatn), Quart. Jour. Aficr. Sci., vol. iii., is;,-,.
(79) STEIN (relations of Acinetx to Ciliata) Der Organismus der Infusionstliitre t
Abth. i., Leipsic, 1S59. (80) STEIN (Dlnonagellata), Der Organismus, &c. t Abth.
iii., Ltipsic, 1883. (81) BERGU (Dinoflagellata), Morpholoy. Jahrb., vii., 1881.
(82) BUTSCHLI (Dinonagellata), Morpholog. Jahrb., x., 1885. (83) KLEBS (Dino-
flagellata), Botan. Ztitung, 1884, pp. 7L'2, 737. (84) GKUBER (nuclei of Ciliiita),
Zeitschr. f. wiss. Zoologie, xi., 1884. (85) FOETTINGER (Opalinopsis, &c.),
Archives de Biologie, vol. ii. (86) ALLMAN (Noctiluca), Quart. Jour. Aficr. Sci.
(new series), vol. xii., 1872, p. 326. (87) CIENKOWSKI (Noctiluca spores), Arch,
f. Afikrosk. Anat., vii., 1871. (88) HERTWIG (Leptodiscus), Jenaische Zeitachr^
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Bulletins de VAcad. Roy. BruxeUes, 1877-78. (90) SURIRAY, Magasin de Zoologie,
1836. (91) ALLHAN (Peridinium), Quart. Jour. Aficr. Sci., iii., 1855. (92) LEIDY,
U.S. Geological Survey of the Territories, vol. xii. (93)CLAi-AREDiiandLACRSiANN,
Etudes sur les Infusoires et les Rhisopodes t Geneva, 1858-61. (E. B.L.)

FIG. XXVII.

FIG. XXVII. Dinoflagellata. This figure is not contained in the
article as published in the Encydopsedia Britannica. It presents
the recent discoveries of Klebs, Biitschli, and Stein.

1. Diagram of the Dinoflagellate Hemidinium. n, nucleus ; /,

flagellum of the transverse groove ; h, flagellum of the vertical
groove.

2. Diagram of the Cryptomonadine Oxyrrhis (to compare with the

preceding). , nucleus; g, the deep fossa or pit in which the
two flagella are affixed; t, the origin of the flagellum which
corresponds with that of the transverse groove of Dino-
flagellata. The second flagellum is seen to be attached near
the mouth of the fossa.

3. Olenodinium cinctum, Ehr., seen from the ventral surface, a,

amyloid granules ; b, eye-spot ; c, chromatophores ; d, flagellum
of the transverse groove; c, flagellum of the vertical groove;
v, vacuole.

4. The same, seen from the hinder pole (letters as in 3).

5. Cuticle of Histioneis cymbalaria, Stein, from the Atlantic, i,

ventral process ; k, cuticular collar ; I, posterior process.

6. The same, seen from the dorsal surface, m, cephalic funnel (k

and I as iu 5).

7. Cuticle of Amphisolcnia globifcra, Stein, from the Atlantic, seen

from the left side, i, narrow ventral processes ; m, cephalic
funnel ; o, the mouth ; ]>, pharynx ; q, the shrunken proto-
plasm.

8. Cuticle of Ornithoccrcus magnificus, Stein, from the Atlantic.

mm', the cephalic funnel ; rr', the two largu rilis of the
cuticular collar (the collar itself similar to k in No. 5 is not
drawn); s, the two rows of dorsal cuticular teeth.

9. Cuticle of Ceratocorys horrula, Stein, from the Southern

Ocean, i, the large frontal plate ; pp' the outgrown margins
of the transverse groove ; v, if, basal plates ; w, one of the/
four frontal horns ; y, the dorsal horn ; y, the ventral horn.

39

rS P N CT E S

(By ][ r . Johnson tiollas, LL.D., F.It.S., Professor of Geology, Trinity College, Dublin.)

THE great advance which has been made during the
past fifteen years in our knowledge of the sponges
is due partly to the vivifying influence of the evolutional
hypothesis, but still more to the opportunities afforded by
novel methods of technique. To the strength and weak-
ness of the deductive method Haeckel's work on the Kalk-
schwamme (6) l is a standing testimony, while the slow but
sure progress which accompanies the scientific method is
equally illustrated by the works of Schulze (20), who by
a masterly application of the new processes has more
than any one else reconstructed on a sure basis the general
morphology of the sponges. In the general progress the
fossil sponges have been involved, and the application of
Nicol's method of studying fossil organisms in thin slices
has led, in the hands of Zittel and others (24, jj), to a
complete overthrow of those older classifications which
relegated every obscure petrifaction to the fossil sponges,
and consigned them all to orders no longer existing.
But, whilst many problems have been solved, still more
have been suggested. An almost endless diversity in
details differentiates the sponges into a vast number
of specific forms; the exclusive possession in common of
a few simple characters closely unites them into a compact
group, sharply marked off from the rest of the animal
kingdom. 2

1 These italic numbers refer to the bibliography which will be
found at page 54.

2 Since this was written, in 1887, four large monographs, includ-
ing considerably over 2000 pages of letterpress, have been published on
the Sponges. Three of these, viz. : Schulze on the Hexactinellidu,
Ridley and Dendy on the Monaxonida, and Sollas on the Tetractind-
lida appear as Reports of the "Challenger" Expedition, the fourth by
Von Leudenfeld on the " Horny Sponges " as a special volume issued
by the Royal Society. With this addition to our knowledge a longer
preface than this would be possible, but for the general student the
following amended classification of the Monaxonida will probably be
found sufficient.

Order. Monaxonida.
Sub-order 1. ASEMOPHORA, Sollas.

Family 1. HOMORAPHTM, Ridley and Dendy. Megascleres either
oxeas or strongyles. No microscleres. Ex. : Halichondria.

Sub-order 2. MENISCOPHORA, Sollas.

The microscleres when present are sigmaspires, sigmas, or cymbas.

Family 1. HETERORAPHEDJE, Ridley and Dendy. Megascleres of
various forms, microscleres never cymbas. Ex.: lihizochalina, O.S.

Family 2. DESMACIDONIM:, O.S. Megascleres usually mouactiual,
microscleres cymbas. Ex.: Desmacidon, O.S.

Sub-order 3. SPIXTHAROPHORA, Sollas.

The microsclere when present is some form of aster.

Group 1. HOMOSCLERA. The spicules are all microscleres.

Family 1. ASTROPEPLID.E. The microscleres are microxeas and
asters. Ex. : Astropeplus, Soil.

Group 2. HKTEROSCLERA, Soil. Megascleres are always present,
and sometimes microscleres.

DEHDS 1. CENTROSPINTHARA, Soil. The microsclere when present
is a euaster.

Family 1. AsiNELLiDa;, O.S. Non-corticate, mesoderm collen-
chymatous, chamber system eurypylous. The skeleton consists of
axial and radial spicular fibres. Ex.: Axinella, O.S.

Family 2. DOUYFLKRID.E, Soil. Non-corticate, mesoderm colleu-

Structure and Form.

Description of a Simple Sponge. As an example of Simple
one of the simplest known sponges we select Ascetta s P n S e -
primordialis (fig. 1), Haeckel. This is a hollow vase-like
sac closed at the lower end, by which it is attached,
opening above by a comparatively large aperture, the
osculum or vent, and at the sides by numerous smaller
apertures or pores, which perforate the walls. Except for
the absence of tentacles and the presence of pores it offers
a general resemblance to some simple form of Hydrozoon.
Histologically, however, it presents considerable dif-
ferences, since, in addition to an endoderm and an

FIG. 1. Ascetta primordialis, Hacckel.
After Uaeckel.

ectoderm, a third or mesodermic layer contributes to
the structure of the walls ; and the endoderm consists of
cells (see fig. 21, g) each of which resembles in all essential
features those complicated unicellular organisms known
as choanoflagellate Infusoria (see PROTOZOA, vol. xix. p.
858). With this positive character is associated a nega-
tive one : nematocysts are entirely absent. The activity

divmatous. Skeleton consisting of oxeas arranged without order.
Ex. : Doryplercs, Sol).

Family 3. TETHYID^E, Vosm. Corticate. Skeleton consisting of
radially arranged oxeas. The microsclere is a spheraster. Ex.:
Tftliyn, Lam.

DEMUS 2. SPIRASPINTHARA, Soil. The microsclere is a spiraster.

Family 1. ScoLOPlDJE, Soil. The cortex is thin and fibrous, with
radially arranged closely-packed microxeas and oxeas. The skeleton
consists of oxeas collected into radially disposed fibres. The micro-
sclere when present is an amphiaster. Ex. : Sculojitts, Soil.

Family 2. SOBHRITIDJE, O.S. Cortex with a skeleton of radially
arranged styles. Microscleres usually absent. The megascleres are
tylostyles. Ex. : Suberites, Nardo .

Family 3. SPIRASTRELLID.E, Ridley and Deudy. The megascleres
are rhabdi or styles. The microscleres are spirasters or discasters.
Ex.: Spiraslrella, O.S.

40

SPONGES

of the Ascetta, as of all sponges, is most obviously mani-
fested, as Grant (j) first observed, by a rapid outflow of
water from the oscule and a gentle instreaming through
the pores, a movement brought about by the energetic
action of the flagella of the
endoderrnic cells. The in-
streaming currents bear with
them into the cavity of the
sac (paragastric cavity) both
protoplasmic particles (such as
Infusoria, diatoms, and other
small organisms) and dissolved
oxygen, which are ingested by
the flagellated cells of the en-
doderm. The presence of one
or more contractile vacuoles in
these cells suggests that they
extricate water, urea, and car-
bonic acid. The insoluble re-
sidue of the introduced food,
together with the fluid excreta,
is carried out through the os-
cule by the excurrent water.
New individuals are produced
from the union of ova and
spermatozoa, which develop
from wandering amoeboid cells
in the mesoderm. The walls
of Ascetta are strengthened by
calcareous scleres, more especi-
ally designated as spicules, FIG. 2. Homoderma sycamim, Lfd.
which have the form of tri- m edian a ^ectlon aW Afte/v a Lend'en!

radiate needles. If we make feid(xabout 6).

abstraction of these we obtain an ideal sponge, which

Haeckel has called Olynthus (6), and which may be re-

Canal System. We shall now trace the several modifi-
cations which the Olynthus has undergone as expressed in
the different types of canal system.

The simple paragaster of Ascetta may become compli- Ascon
cated in a variety of ways, such as by the budding off tJT 6 -
from a parent form of stolon-like extensions, which then
give rise to fresh individuals, or by the branching of the
Ascon sac and the subsequent anastomosis of the branches;
but in no case, so long as the sponge remains within the
Ascon type, does the endoderm become differentiated into
different histological elements. The most interesting
modification of the Ascon form occurs in Homoderma sy-
candra (i2\ in which from the walls of a simple Ascon
csecal processes grow out radiately in close regular whorls,
each process reproducing the structure of the parent
sponge (figs. 2, 3). From this it is but a short step to
the important departure which gives rise to the Sycons.

In the simplest examples of this type the characters of Sycon
Homoderma sycandra are reproduced, with the important type,
exception that the endoderm lining the paragastric cavity
of the original Ascon form loses its primitive character,

FIG. 3. Humodcrma syctiiulm, Lfd. Transverse section, showing radial tubes opening
into central naragustric cavity. After V. Lendeiiteld (xabout !-)

garded as the ancestral form from which all other sponges
have been derived. To give greater exactness to our ab-
straction we should perhaps stipulate for the Olynthus a
somewhat thicker mesoderm and more spherical form than
a decalcified Ascon presents.

FIG. 4. Heteropegnwnodus-gordii, Pol. Part of a transverse section. The straight
lines indicate spicules ; the poriferous surface is uppermost; the branching
radial tubes are rendered dark by numerous small circles representing
clioauocytes. After PolejaefT, ' ' Challenger " Report ( X 50).

and from a layer of flagellated cells becomes converted
into a pavement epithelium, not in any distinguishable
feature different from that of the ectoderm. The
flagellated cells are thus restricted to the caecal
outgrowths or radial tubes. Concurrently with
this differentiation of the endoderm a more abun-
dant development of mesoderm occurs. In some
Sycons (Sycaltis, Hk.) the radial tubes remain
separate and free; in others they lie close together
and are united by trabeculte, or by a trabecular
network, consisting of mesodermic strands sur-
rounded by ectoderm (fig. 4). The spaces between
the contiguous radial tubes thus become converted
into narrow canals, through which water passes
from the exterior to enter the pores in the walls
of the radial tubes. These canals are the " inter-
canals " of Haeckel, now generally known by their
older name of incurrent canals. The openings of
the incurrent canals to the exterior are called
pores, a term which we have also applied to the
openings which lead directly into the radial tubes
or paragastric cavity; to avoid ambiguity we shall
for the future distinguish the latter kind of open-
ing as a prosopyle. The term "pore" will then be

restricted to the sense in which it was originally used by
Grant. The mouth by which a radial tube opens into the
paragaster is known as a gastric ostimn. In the higher
forms of Sycons the radial tubes nolonger arise as simple out-
growths of the whole sponge- wall, but rather as outgrowths

SPONGES

41

of the emloderm into the mesoderm, \vliirh, together with
the ectoderm, exhibits an independent growth of its own;
and this results in the formation of a thick investment,
known as the cortex (fig. 5), to the whole exterior of the

'

Kb. agon
type.

Fio. 5. Utc Argcnted, Pol. Fart of a transverse section. The concentric circles,
indicating transviTsr sections of spicules, lie within the cortex. After Pule-
jaeff, " Challenger" Report ( x 100).

sponge. The radial tubes may branch, Heteropegma (fig.
4). If the branches are given off regularly, as the radial
tubes were in the first plan, and if at the same time the
original radial tube exchanges its flagellated for a pave-
ment epithelium, a structure as shown in fig. 6 (Polejna

Fio. 6. Polejna connexiva, Pol. Part of a transverse section. E, excurrent
canals, into which the flagellated chambers open. After Poleiaeff, " Challenger"
Effort (KM).

connexiva, Pol.) will result. This form might also be
brought about by unequal growth of the gastral endoderm
leading to a folding of the inner part of the sponge-wall.
Very little direct evidence exists as to which of these two
plans has actually been followed. Phylogenetically the
transition from a simple Ascon to the most complicated
Sycon can be traced step by step ; and ontogeny shows
that such a Sycon form as Grant in r<iphanus passes through
an Ascon phase in the course of its larval development.

Returning to the ancestral form of sponge, Olynthus,
let us conceive the endoderm growing out into a number
of approximately spherical chambers, each of which com-
municates with the exterior by a prosopyle and with the
paragastric cavity by a comparatively large aperture, which
we may term for distinction an apapyle; at the same time
let the endoderm lose its flagellated character and become

converted into a pavement epithelium, except in the
spherical chambers. Such a form, called by llaeckel
"dyssyciis," maybe more briefly named a ]{lni<i<,ii from
the grape-like form of its flagellated chambers, which differ
from those of a Sycon both by their form and their smaller
dimensions. The Khagon occurs as a stage in the early
development of Plakiiia monoloji/ui (Sehulxe) and llt'iiiera,
fcrtitis (9) (fig. 7); a calcareous sponge which appears to

FIG. 7. Vertical section of a Rhagon, partly diagrammatic, o, oseulc ; p,
paragaster. After Keller (X about 100).

approach it somewhat is Leucopsis pedunndatn, Lfd. By
the folding of the wall of a Ehagon, or by its outgrowth
into lobes, a complicated structure such as that of Plakina
monolopha (20) (see fig. 26 /) results. This is character-

Fio. 8. Transverse section across an excurrent. canal and surrounding choano-
some of Cydoniitm eosuster, Soil, e, excurreut canal ; /, flagellated chambers
communicating with it. by aphodal canals ; ;., an incurrent canal cut across ; 5,
a sterraster ; o, an oxea cut across. After SoUas, " Challemjcr " .Report (x 125).

ized by the chambers retaining their immediate communi-
cation with the incurrent and excurrent canals, opening
into the latter by the widely open apopyle and receiving
the former by one or
several prosopyles. This ','
may be termed the e ury-
pylous type of Ehagon
canal system. The fold-
ing of the sponge -wall
may be simple, as in the
example given, or too , ~<},
complex to unravel. In
higher forms of sponges
(Geodinidx, Sttlhttidx)
the chambers cease to
open abruptly into the
excurrent canals : each is
prolonged into a narrow
canal, apfiodus, or alii(a,
which usually directly,
sometimes after uniting
with one or more of its PI Q. 9. mplodaTcanal system in Cort;?;,n.

fellows Opens into an candelabrum, O.S. e, excutrent canal ; the
. ,, incurrent canal is ><li"\ni <*n the k-ft-hand
excurrent canal. llie side, near its commencement in the cortex,
prosopyles, now. restrict- After F - E - Scllulze < x :
ed to one for each chamber, may remain unchanged in
character, or at the most be prolonged into very short

F

42

SPONGES

tubes, each a prosodus or aditus (fig. 8). This may be
termed the aplwdal or racemose type of Rhagon system,
since the chambers at the ends of the aphodi radiating
from the excurrent canal look like grapes on a bunch. As
Haeckel, however, has used "racemose" in a different sense,
we shall adopt here the alternative term. By the exten-
sion of the prosodal or adital canals into long tubes a still
higher differentiation is reached (fig. 9). This, which from
the marked presence of both prosodal and aphodal canals
may be termed the diplodal type of the Rhagon canal
system, occurs but rarely. Chondrosia is an example.

The following scheme will render clear the foregoing
distinctions :

1. Ascon type : simple, ex. Ascetta, Hk. ; strobiloid, ex. Homo-

derma, Lfd.

2. Sycon type : simple radial tubes, ex. Sijcctta, Hk. ; branched

radial tubes (cylindrical chambers), ex. Hctcropegma, Fl. ;
chamber-layer folded, ex. Polcjna, Pol.

3. Rhagon type : eurypylous, with several prosopyles to each

chamber, ex. S/jtmyelia ; with a single prosopyle to eacli
chamber, ex. Oscarctta, Thenca ; aphodal, aphodal canals well
developed, ex. Gcodia, Link. : diplodal, with both aphodal
and prosodal canals well developed, ex. Chondrosia, O.S.

In the case of the calcareous sponges Polejaeff has argued
forcibly that the eurypylous type arises directly from the
Sycon and not from the Rhagon. It is therefore doubtful
how far the Rhagon in other sponges is a primitive form
derived directly from an Olynihus, or whether it may not
be a secondary larval state resulting from the abbreviated
development of a former Sycon predecessor. Whatever
may have been its past history, the Rhagon serves now at
all events as a starting-point for the development of the
higher forms of canal system.

Subder- In the higher Rhagons, as in the Sycons, further com-
ma l plications ensue, owing to an independent growth of the
cavities. ex t erna i ectoderm and the adjacent mesoderm. While the
endoderm, with its associated mesoderm, is growing out
or folding to form the excurrent canal system, the super-
ficial mesoderm increases in thickness, and the ectoderm,
extending laterally from the sides of the incurrent sinuses,
burrows into it, parallel to the surface of the sponge.
Thus it forms beneath the skin (i.e., the layer of superficial
mesoderm and investing ectoderm) cavities which may be
either simple and spacious or be broken up into a number
of labyrinthine passages by a network of mesoblastic
strands (invested with ectoderm) which extend irregularly
from roof to floor of the chamber. These cavities are
known as subdermal chambers.

With the appearance of subdermal chambers the sponge
Ecto- becomes differentiated into two almost independent regions,
some, all ou ter or ectosome and an inner or choanosome, which is
some" " characterized by the presence of flagellated chambers.
The ectosome forms the roof and walls of the subdermal
chambers, and is in its simplest form merely an investing
skin ; but in a large number of sponges it acquires con-
siderable thickness and a very complicated histological
structure. It is then known as a cortex. The thickening
which gives rise to a cortex takes place chiefly beneath
those parts of the skin which are not furnished with pores.
Beneath the pores in this case collected into sieve-like
areas dome-like cavities are left in the cortex ; they open
freely into the subdermal cavities below and their roof is
formed by the cribriform pore membrane above. In many
sponges (Geodia, 8/rl/et/a) the cortical domes are constricted
near their communication with the subdermal cavity (sub-
cortical crypt) by a transverse muscular sphincter, which
defines an outer division or ectnchone from an inner or
endochone (fig. 10), the whole structure being a chone.
Chone. The endochone is frequently absent (fig. 10). The early
development of the cortex has scarcely yet been studied.
In Stdlettaphrissens($o\\,), one of the "Challenger" Stel-

lettidx, an early form of the sponge (fig. 11), shows the
choanosome already characteristically folded within the
cortex, which forms a com-
plete not-folded envelope
around it. The roots of
the incurrent sinuses form ,
widely open spaces imme-
diately beneath the cortex
and are the rudiments of ;
subcortical crypts. Again,
in some sponges a part of i
the endoderm and asso-
ciated mesoderm may like- 1 j(
wise develop independ- 1| /
ently of the rest of the /J
sponge, as in the Hexac-
tine/lida, where the choa-
nosome forms a middle
layer between a reticula-
tion of ectosome on
one side and of endoderm ;
and mesoderm, i.e., em.li-
some, on the other. Fin-
ally, the attached or lower Fl (
half of a Rhagon may de-
velop in an altogether dif-
ferent manner from the ,

The dotted circles in the cortex are sterr-
Otner or upper hall, the asters connected by fibrous strands.

endoderm not producing After Soiias 1 "CtaZtoff-Bepor(x 73).

any flagellated chambers. In this case the upper portion
alone is characterized by the flagellated chambers, which
are the distinctive mark of a sponge, and hence may be

Uj

10. Section through tho cortex of (> Endo-
Jtnnuiti eososfer, SolL, showing the pore- some,
sieve overlying the chone, which com-
municates through a sphinctrate aperture
with the subcortical crypt, lying in the
choanosome with its flagellated chambers.

Fin. 11. Young sponge of stelletta pTirissena, Soil. Longitudinal median sec-
tion, showing the clnaiuisomi' lol.U'd within the cortex, o, oscnle. After
Sollas, " Cltatlenijtr" Rc^n-t (x50).

called the spongomere ; the lower half, which consists of
all three fundamental layers, may be called the hypomtre.
The form and general composition of sponges are ex-
ceedingly various and often difficult to analyse, presenting,
along with some important differences, a remarkable general
resemblance to the Co-lentem in these respects. Like Oscule.
them, some sponges are simple, and others, through
asexual multiplication, compound. The only criterion by
which the individual sponge can be recognized is the oscu-
lum ; and, as it is frequently difficult, and in many cases
impossible, to distinguish this from the gastric opening of
a large excurrent canal, there are many cases in which the
simple or compound nature of the sponge must remain
open to doubt. The oscule may also fail (lipostomosis),
and so may the paragastric cavity (lijn.il/as/rrisiif) ; the
problem then becomes insoluble. The loss of the oscule

SPONGES

Mineral
spicules.

may in some cases be duo to the continued growth of
several endodermal folds towards the exterior, with a
corresponding absorption of the mcsoderm and ectoderm
which lie in the way, till the folds penetrate to the ecto-
derm and open at the exterior, thus giving rise to exeurrent
openings, which are not readily distinguishable from pores.
At the same time the original osculum closes up and
entirely disappears. Lipogastrosis, on the other hand,
may be produced by the growing together of the roots of
the choanosomal folds, thus reducing the paragastric cavity
to a labyrinth of canals, which may easily be confounded
with the usual form of exeurrent canals. While in some
sponges the original oscule is lost, in others secondary
independent openings, deceptively like oscules, are added.
This pseudostomosis is due to a folding of the entire sponge,
so as to produce secondary canals or cavities, which may
be incurrent (vestibular) or exeurrent (cloacal), the opening
of the latter to the exterior being termed a false oscule
or pse-udostvme. The faulty use of the term oscule for
what is neither functionally nor morphologically a mouth
is here obvious, for in one sense the oscule is always a
pseudostome ; it would be better if the term pseudojjroct
could be substituted.

Skeleton. Skeleton. All sponges, except three or four genera be-
longing to the Myxospongise, possess some kind of skeletal
structures. They may be either calcareous or silicious or
horny scleres, the latter usually having the form of fibres,
which sometimes enclose silicious needles (spicules) or
foreign bodies introduced from without. Foreign bodies
also contribute to the formation of the skeleton of some
silicious sponges, and occasionally form the entire skeleton,
no other hard parts being present.

Mineral scleres usually occur in the form of spicules.
The spicules of calcareous sponges consist of carbonate of
lime, having the crystalline structure and other properties
of calcite (29). Each spicule, so far as its mineral com-
ponent is concerned, is a single crystal, all the molecules
of calcite of which it is built up being similarly oriented.
On the other hand, its form and general structure are
purely organic. Its surfaces are always curved, and usually
it has the form of a cone or combination of cones, each of
which consists of concentric layers of calcite surrounding
an axial fibre of organic matter, probably of the same
nature as spongiolin or spongin, the chief constituent of
the fibres of horny sponges. A thin layer of organic matter,
known as the spiaile sheath, forms an outer investment to
the spicule and is best rendered visible as a residue by
removing the calcite with weak acid. Silicious spicules
consist of colloid silica or opal, and hence can be distin-
guished from calcareous by having no influence upon polar-
ized light. Structurally the two kinds of spicules present
no important difference. The spicules of different sponges
differ greatly both in form and in size. They may be
conveniently divided into two groups, minute or flesh
spicules, which usually serve as the support of a single cell
only (microaderes), and larger or skeletal spicules, which
usually contribute to the formation of a more or less con-
sistent skeleton (meffasclereii). The distinction is not one
that can be exactly defined, and must so far be regarded
as of a provisional nature. There is usually but little diffi-
culty in applying it in practice, except in some doubtful
cases where large spicules do not form a continuous skeleton,
or in others where flesh spicules appear to be passing into
those of larger size. It is indeed highly probable that all
large spicules have originated from flesh spicules (/.?).

(1) Monaxon Biradiate Type (rhabdus). By far the
commonest form is the oxea, a needle-shaped form pointed
at both ends and produced by growth from a centre at the
same rate in opposite directions along the same axis. It
is therefore uniaxial and eguibiradiate (fig. 12). (2) Mon-

Type (stylus). By the suppression of one
of the rays of an oxea, an acuate spicule or stylus results
(fig. 12 I). (3) Triaxon Trira<l!nte Ti/jie. Linear growth

\

V

FIG. 12. Typical megascleres. , rhabdus (moiiaxon diactine); b, stylus
(monaxon iiionactim-) ; i', trind (tri;u\on triactine); d, call limps (trtraxon
U'tractinO ; i', triaxnli hexartiiR-; /, <li-snia nf an aiioiiiockuline Lithistid
(polyaxon) ; ff, sterraster (iiolyaxon) ; /(, radial section through the outer
part of g, showing two actine.s soldered togrtlnT l>y inlrrvnilng silica, tin-
in ends terminating in recurved spines ana the axis traversed by a eentral
fibre.

from a centre in three directions inclined at an angle of
120 to each other gives rise to the primitive form of tri-
radiate spicule so eminently characteristic of the calcareous
sponges, but by no means confined to them (fig. 12 <). (4)
Tetraxon Quadriradiate Type (Culthi-ups). Growth from a
centre in four directions inclined at about 110" to each
other produces the primitive quadriradiate form of the
Tetractintllida and of some calcareous sponges (fig. 1 2 d).
(5) Sexradiate Type. Growth in six directions along three
rectangular axes produces the primitive sexradiate spicule
of the Hexactindlida sponges (fig. 12 e). (G) Multiradiate
Type. Extensions radiating in many directions from a
centre produce a stellate form (fig. 12/). (7) Spherical
S'-l'Ti-f. Concentric growth of silica about an organic
particle produces the sphere, which occurs as a reduction
of the rhabdus in some species of Peecillfisti-a, or as an
overgrown globule (flesh spicule) in Caminus.

Usually conical, the spicular rays often become cylindrical ; usu- Uniaxial
ally pointed (oxeatc) at the ends, they are also frequently rounded type,
off (strongylate), or thickened into 'knobs (tylotatc), or branched
(cladosc). Their growth is not always rigorously confined to a

A

Mega-
scleres.

FIG. 13. Modifications of monaxon type, a, strongyle ; 6, tylote ; r, oxea ; rf,
tylotoxea ; e, tylostyle ; /, style ; g, spined tylostyle ; h, sagittal tried (a
triaxon form derived from the nioiiaxon) ; j, oxytylote ; k, anatriaene ; ?, pro-
trijcne; m, orthotrirene ; u, dichotriitnc ; o, centrotrkene ; ji, amphitneene
(this is trichocladow) ; ry, crcpiilwl strongyle (basis of Khabdoorepid I.iihislid
di-sma); /, young form of Rhabdocrepid desnia, showing crepidial strongyle
coated with successive layers of silica ; , Rhahdncrepiil di'sma fully gro\vn.
The dotted liue through the upper figures marks the origin of the actiues.

straight line : frequently they are curved or even undulating. They
are also liable to become spined, either by mere superficial thicken-
ing or by a definite outgrowth involving the axial fibre (fig. 13 g, h).
The rhabdus if pointed at both cuds is known as an oxea (fig.
13 c) ; if rounded at both ends as a slrongylc (fig. 13 a) ; if knobbed

44

SPONGES

at both ends as a tylote (fig. 13 b) ; the tylote if pointed at one end
is a tylotoxea (fig. 13 d) ; the strongyle similarly becomes a stronyyl-
oxea. These last two forms are with difficulty distinguished from
the stylus, which is usually pointed at the end, and strongylate (fig.
13/) or tylotate (fig. 13 e) about the origin. A particular case of
the cladose rhabdus, but one of the most frequent occurrence, is
the trixnc ; in this form one ray of a rhabdus ends in three branches,
which diverge at equal angles from each other. The rhabdus then
becomes known as the shaft or rhabdomc, and the secondary rays
are the amis or cladi, collectively the head or cladomc of the spicule.
The arms make different angles with the shaft : when recurved a
grapnel or anatrissne is produced (fig. 13 k), when projecting forwards
a protrixne (fig. 13 I), and when extended at right angles an ortho-
tri&ne (fig. 13 in). The arms of a triiene may bifurcate (dichotriirnc)
once (fig. 13 n), twice, or oftener, or they may trifurcate. Again,
they may extend laterally into undulating lamellae, or unite to form
a disk, the tri;ene character of which is indicated by the included
axial fibre. The shaft may also become trifid at both ends, amjihi-
trixnc (fig. 13 p), and the resulting rays all bifurcate, or the elndome
may arise from the centre of the rhabdome, centrotriaine (fig. 13 o).
Amongst one group of Lithistid sponges (Mhabdocrcpida) the normal
growth of a strongyle is arrested at an early stage ; it then serves
as a nucleus upon which further silica is deposited, and in such a
manner as to produce a very irregularly branching sclere or dcsina
(fig. 13 s), within which the fundamental strongyle can be seen en-
closed. In such a desina no axial fibre besides that of the enclosed
strongyle is formed.

Triradi- The chief modification of the triradiate spicule is due to an elonga-

ate type, tion of one ray, distinguished as apical, the shorter paired rays
being termed basal, and the whole spicule a sagittal triradiate. The
angle included by the basal rays is usually over 120 (fig. 14 a).

Quadri- Some or all of the rays of the primitive calthrops (fig. 14 b) may

radiate

type.

FIG. 14. Modifications of the triaxon and tetraxon types, n, sagittal triradiate
or tri"d ; fr, calthro]is ; c, candelabra (a polycladose microcaltlirops) ; d, a
spiued microealthrops ; c, Tctradadiue Lithistid desina.

subdivide into a number of terminal spines candelabra (fig. 14 c} ;

or some or all of them may bifurcate once or twice and finally

terminate by subdividing into numerous variously shaped processes ;

such a trtmcludinc desnia (fig. 14 c) characterizes one division of the

Lithistid sponges.

Sexradi- By the excess or defect of one or more rays a series of forms such
ate type, as are represented in fig. 15 arise. In the oxea, which results from

FIG. 15. Modifications of the triaxon hexactine type, a, dagger ; 6, c, two
varieties of pinnulus ; d, ainphidisk ; c, pentactine ; f, staurus ; g, dermal
rhabdus. After Schulze.

the suppression of all raj's but two, the sexradiate character is some-
times preserved by the axial fibre, which gives off two or four pro-
cesses in the middle of the spicule where the defective arms would
arise. Let fig. 12 c represent a regular sexradiate spicule with its
four horizontal arms extended beneath the dermis of its sponge ;
the over-development of the proximal ray and a reduction of the
distal ray produce a form known as the dagger (fig. 15 a) ; the
suppression of the proximal ray and the development of spines pro-
jecting forwards on the distal ray produce the piimulns (fig. 15 b, c) ;
the suppression of both proximal and distal rays gives the stmini*
(fig. IS/), and the suppression of two of the remaining horizontal
rays a dermal rhabdus (fig. 15 g). The suppression of a distal ray,
excessive development of a proximal ray, and recurved growth of
the remaining rays produce an anchor. In Hijalonema (glass rope
sponge:) anchors over a foot long occur, but their arms or teeth are
not restricted to four, and the axial fibre gives off its processes
before reaching the head of the spicule. Such a grapnel helps to
support the sponge in the ooze of the sea-bed. Other character-

"yj
FIG. 10. a, uncinaria ; b, clavula ; c, scopularia. After Schulze.

istic spicules belonging to sponges distinguished by sexradiate
spicules are the following ; the uncinaria (fig. 16 a), a spiuose

oxea with the spines all pointing one way ; the clavula, a tylotate
form with a toothed margin to the head (fig. 16 b); the scopularia
(fig. 16 c), a besom-shaped spicule with tylotate rays, which vary
in number from two to eight ; the amphldisk (fig. 15 d), a shaft
terminating at each end in a number of recurved rays. "When the
sexradiate spicules of the Hcxactincllida unite together in a manner
to be described later, the rays may be bent in a variety of ways
out of the triaxial type, so that the sexradiate character alone
remains.

Mitltiradiatc Type. The rays of an aster as of other spicules Multi-
may be spined or tylotate. In one remarkable form known as a radiate
sterraster (fig. 12 g, h), and characteristic of the family Gcodinidx, type,
the rays are almost infinite in number, and coalesced for the greater
part of their length ; the distal ends, however, remain separate,
and, becoming slightly tylotate, are produced into four or live re-
curved spines, which give attachment to connective tissue fibres
by which adjacent sterrasters are united together.

In one aberrant group of Lithistid sponges (Anomocladina) the
skeleton is formed of desmas, which are multiradiate, each present-
ing a massive centrum (with an included cavity) produced into a
variable number (4 to 8) of rays, which rays terminate in expanded
ends (fig. 12/).

It is doubtful whether a distinction between megascleres and Micro-
microscleres can be maintained in the calcareous sponges, unless scleres
the minute oxeas which occur in Eilhardia, schuhci, Pol. (16), are
to be referred to this group. They are widely distributed through-
out the silicious sponges, and by their different forms afford charac-
ters of the highest importance in classification.

One of the simplest forms is the sigmaspire (fig. 17 a, b) it looks
like the letter C or S, according to the direction in which it is

FIG. 17 Microscleres. n, !>, sigmaspire viewed in different directions, n, along

, , ,

axis, and I, obliquely; c, toxaspire ; d, spiraster ; e, saniclaster; /, amplii-
aster ; g, sigina or cymba ; h, cynilia, with three pteraat each end, the central
one a proral pteron aud the lateral, pleural ptera ; j, one end of another form
of cymba, showing seven ptera ; 1;, monopteral cymba, proral ptera only,
developed at ends, tropidial ptera much enlarged ; /, oocymba, in which proral

tylote ; s, microxea (q, r, and s arc reduced asters) ; (, rosette,
viewed, its actual form being that of a single turn of a cylindrical
spiral. A turn and a part of a turn of a spiral of somewhat higher
pitch than that of a sigmaspire gives the toxaspire (fig. 17 c) ; a con-
tinued spiral growth through several revolutions gives the poly-
spii-c. The sigmaspire becoming spined produces the spiraster or
spinispinda (fig. 17 d) ; this, by losing its curvature, becomes the
sanidastcr (fig. 17 <), and by simultaneous concentration of its spines
into a whorl at each end, the amphiastcr (fig. 17/). By reduction
of the spire the spiraster passes into the stellate or aster (fig. 17 n).
A thickening about the centre of the aster produces the sphcrastcr
(fig. 17m), allied to which is the sterraster. By a reduction in the
number of its rays the aster becomes a minute calthrops, from which,
by increased growth, the skeletal calthrops may very well be derived ;
by further reduction to two rays a little rhabdus or microrabd re-
sults, and of this numerous varieties exist, of which the oxeate
microrabd is the most interesting, since it only differs in size from
the commonest of all skeletal spicules, the oxeate or acerate rhab-
dus. The sigmaspire is formed as a superficial spiral thickening
in the wall of a spicule cell or scleroblast ; as superficial deposits
also the next group of spicnles, the so-called anchorates, arise.
Take a hen's egg as the model of a scleroblast, draw round it a
broad meridional band, interrupted only on one side, for 30 above
and below the equator ; this will represent a truly C-sliMpcd spicule,
which differs from a sigmaspire by the absence of spiral twist.
It may be termed a cimilifi (fig. 17 .7). The back of the "C" is the
keel or tropis; the points are the prows or prorae. Now broaden out
the prora on the eggshell into oval lobes (proral plercs) ; and from
each pole draw a lobe midway between the prora and the tropis
[pleural ji/n-f/i), and a common form of auchorate, the

SPONGES

45

results (tig. 17 /(). The pterocymlia is subject to considerable modi-
fications: tin; prows may I"' simil;ir i/inmo/i/vi/w/) ar dissimilar
(hetcroproral) ; the ptcivs may In 1 lamellar or lingual ; additional
lainclhc (ti'iijiii/iiil jiti-i'e.t'i may be produced by a lateral nut growth
of the keel (tig. 17 ) ; and by growing towards tin 1 equal or tin 1
opposed proral ami pleura! ptcres may conjoin, producing a spicnlo
of two meridional bands (oocymfes ; iig. 170- A curious group of
flesh spieulrs are the //'/r/i/Y.x In this group silica, instead of being
deposited in concentric coatings around an axial lilire, forms within
the sclcroblast a sheaf of immeasurably line librilhc or trichites,
which maybe straight (fig. 17 ) or twisted. The triehite sheaf
may be regarded as a tibrjllated spicule. Triehite sheaves form in
some sponges, as Dragmastra (zj), a dense aecumulation within
the cortex. In Hexactinellid sponges the rays of the aster are
limited to six, arranged as in a primitive sexradiate spicule, but
divided at the ends into an indefinite number of slender filaments,
which may or may not be tylotate, rosettes (fig. 17 0.
Spongiu Spongin is a horny substance, most similar to silk in
Bcleres. chemical composition, from which it differs in being in-
soluble in an ammoniacal solution of copper sulphate
(cuproso-ammonium sulphate). In Darwinc/la awta, F.
Miiller, it occurs in forms somewhat resembling tri-,
quadri-, and sex-radiate spicules. But usually the spongin
skeleton takes the form of fibres, consisting of a central
core of soft granular substance around which the spongin
is disposed in concentric layers, forming a hollow cylinder
(fig. 23 I). The relative diameters of the soft core and
of the spongin cylinder differ greatly in different sponges.
The fibres branch so as to form antler-like twigs or bushy
tree-like growths, or anastomose to form a continuous net-
work, as in the bath sponge (Suspongia qfflcinalis). The
detailed characters of the network differ with the species,
and are useful in classification. In lanthdla certain cells
(sponginblasts) become included between the successive
layers of the spongin cylinder, and their deep violet colour,
contrasting with the amber tint of the spongin, renders
them very conspicuous.

Union of In some sponges the scleres are simply scattered through the
scleres luesoderm and do not give rise to a continuous skeleton, Carl i,' in ,,i,
into a ChomlfiUfi, Th i-ouilus. In the Calcarca and many silicious sponges
skeleton, they are dispersed through the mesoderm, but so numerously that
by the overlapping of their rays a loosely felted skeleton is pro-
duced. In the calcareous sponges the spicules are frequently regu-
larly disposed ; and in the Sycons in particular a definite arrange-

FIG. IS. Articulate ami inarticulate tubar skeletons of calcisponges. a, articu-
late ; !), inarticulate skeleton. After Haeckd.

incnt, on two plans, the articulate and iunrticidnlc, can be traced
in the skeleton of the radial tubes. On the latter plan the triradi-
ate or quadriradiate spicules, the apical rays of which are of con-
siderable length, are arranged in two sets, one having the basal
rays lying in the mesoderm of the paragastral wall and the other
with the corresponding rays in the dermal mesoderm. The apical
rays of each set lie in the mesoderm of the radial tubes parallel to
their length, but pointing in opposite directions (fig. IS I). In the
articulate division numerous spicules, small in comparison with
the size of the radial tubes, form a series of rows round the tubes,
their basal rays lying parallel to the paragastric surface and the
apical pointing towards the ends of the radial tubes (fig. 18 o).

In the Siliciajimiyia sheaves of long oxeate spicules radiate from
the base of the sponge if of a plate-like form, or from the centre if
globular, and extend to the surface. If triaeues are present their
arms usually extend within the mesoderm immediately below the

dermal surface dig. 10). Single spicules reach from centre to sur-
face only ill small sponges. As the sponge increases in sixe, the
spicules must either correspondingly lengthen, or fresh spicules
mii-t be added, if a
continuous skeleton is
to be formed. The
latter is the plan fol-
lowed in fact : the ad-
ditional spicules over-
lap the ends of those
first formed like the
fusiform cells in a
woody fibre. YVitli the
formation of a fibre,
often strengthened by
spongin or bound to-
gether with connective
tissue, there appears to
lie a tendency for the
constituent spicules to
diminish in size, and
the length of each in
the most markedly Fie. 10. Morle of arrangement of spicules in a
fibrous sponges is ill- >"""!! St.-llottid sponge, Dragmnstra nonaani,
significant when com- *' M ' Altw Sollas -

pared with the length of the fibre. The spiculnr fibre thus
formed may lie simple or echinated by spicules either similar to
those which form its mass or different. More usually they are
different, and generally styles, often spiuose about their origin.
The spongiu which sometimes cements together the spicules of a
fibre may progressively increase in quantity and the spicules di-
minish in number, till a horny fibre containing one or more rows
of small oxeas results. In an echinated fibre the axial spicules
may disappear and the echinating spicules persist. Finally all
spicnles may be suppressed and the horny fibre of the Ceratose
sponges results. The horny fibres may next acquire the habit of
embedding foreign bodies in their substance, though foreign en-
closures are not confined to the ('ernlo.vt, but occur in some Silici-
sponyiai as well. The included foreign bodies may increase in
quantity out of all proportion to the horny fibres ; and finally the
skeleton may consist of them alone, all spongiu matter having
disappeared.

In the Lithistid sponges a skeleton is produced by the articula-
tion of desmas into a network. The rays of the desrnas (figs. 12/,
13 s, 14 c) terminate in apophyses, which apply themselves to some
part of adjacent desmas, either to the centrum, shaft, arms, or
similar apophyses, ami then, growing round them like a saddle on
a horse's back, clasp them firmly without anchylosis. Thus they
give rise to a rigid network, in conjunction with which fibres com-
posed of rhabdus spicules may exist. In the HcxactincUida both
spicular felts and fibres occur, and in one division (Diclyonina) a. rigid
network is produced, not, however, by a mere clasping of apophyses,
but by a. true fusion. The rays of adjacent spicules overlap and a
common investment of silica grows over them.

Histology.

The ectoderm usually consists of simple pavement Ecto-
epithelial cells (pinnococytes), the margins of which can derm,
be readily rendered visible by treatment with silver nitrate,
best by Banner's method. 1 The nucleus and nucleolus
are usually visible in preparations made from spirit speci-
mens, the nucleus being often readily recognizable by its
characteristic bulging beyond the general surface. In some
sponges (ThecKjJtorct) the epithelium, may be replaced
locally by columnar epithelium, and the cells of both pave-
ment and columnar epithelium may bear flagella (AplysUla
violacect, Oscarella lobitlaris). The endoderm presents the Endo-
sarue characters as the ectoderm, except in the Ascons and derm,
the flagellated chambers of all other sponges, where it is
formed of collared flagellated cells or choanocytes, cells
with a nearly spherical body in which a nucleus and nucleo-
lus can be distinguished and one or more contractile vacu-
oles. The endoderm extends distally in a cylindrical neck
or collum, which terminates in a long flagellum surrounded
by a delicate protoplasmic frill or collar (fig. 21r/). In
Tetractinellida, and probably in many other sponges cer-
tainly in some the collars of contiguous choanocytes
coalesce at their margins so as to produce a fenestrated
membrane, which forms a second inner lining to the flagel-

1 S. F. Manner, " On a Method for the Silver Staining of Marine
Objects," Mitth. Zooloy. Staliun ~i> Xaijtcl, 1SS4, p. 445.

46

SPONGES

lated chamber (fig. 20, ii.). The presence of this membrane
enables us readily to distinguish the excurrent from the

Fio. 20. Choanocytes with coalesced collars, (i.) Longitudinal section through
two flagellated chambers of Anthastra <:n/n/nunis, Soil.; j, prosopyles; c,
aphodal canals leading from the flagellated chambers ; e, excnrrent canal ;
the tissue surrounding the chambers is sarcenchyme (X360). (ii.) Diagram
showing the fenestrated membrane (in) produced by coalesced collars of
Choanocytes. After Sollas, " Challenger" Report.

incurrent face of the chamber, since its convex surface is
always turned towards the prosopyle. In sponges with an

FIG. 21. Histological elements, a, collcncytes, from Tlmicn mnricata; b,
chondrenchyrnr, from enrtrx <il' I'm-lir'nuu fi/uli'tuhn/M (lln 1 nnsliadrd bodies
are niicrosch-ivs); r, pv.strni-liynir. from r>i>1i//tiiiitt<nt<i ji>lni*t,>ui (partly dia-
grair.inatiV) ; d. deswacyte, from /v<i[/m.</m tun-muni i >', ii.vorytcs in con-
nexion with coilrnryl.-s, tViim Oinachyn Imrhiin; f, thesocyte, from Thrum
mitricatfi\ g t choanocyte, from Xii<-im<lr m^/m/Mi* ; ft-fi, scleroblasts /<, of

a young oxra, Ii i an iMnbiyo of ( 'ruini lln enmiwm ; i, ol'a fully grown oxea,

fi'oin an adult <'. rnniiuin ; j, urthotriM-m-, with associated scleroblast from
x/rll</i"; /,,Mta tetracladine desma, trom Tlirourll" *tr;,,i,<>/i ; /, of a sigma-
sjthv, tViuii rrnuirU'i cranium; m, of an orthodragma, 1'rom Disyrtnga '/is.
similis ; n, of a stcrrast.er, from Gcudia burretti. Figs, b and ;/ al'lrr Schulze,
the others after Sollas.

aphodal canal system the flagellated chambers usually pass
gradually into the aphodal canal, but the incurrent canal

enters abruptly. This abrupt termination of the incurrent
canal appears to mark the termination of the ectoderm
and the commencement of the endoderm. The flagellated
chambers differ greatly in size in different sponges, and
evidently manifest a tendency to become smaller as the
canal system increases in complexity; thus Sycon are always
larger than Ehagon chambers, and eurypylous than aphodal
Rhagon chambers. In most sponges except the Ascons the
mesoderm is largely developed, and in many it undergoes Meso-
a highly complex histological differentiation. In its com- de rm.
monest and simplest form it consists of a clear, colourless,
gelatinous matrix in which irregularly branching stellate
cells or connective tissue corpuscles are embedded ; these
may be termed collenc-ytes (fig. 21 a) and the tissue collen-
chyme. In the higher sponges (Geodia, Stelletta) it consists
of small polygonal granular cells either closely contiguous
or separated by a very small quantity of structureless jelly,
and in this form may be termed sarcenchyme (fig. 20).
Collenchyme does not originate through the transformation
of sarcenchyme, as one might expect, for it precedes the
latter in development. Schulze (20), who has compared
collenchyme to the gelatinous tissue which forms the chief
part of the umbrella of "jelly-fish," describes it as becoming
granular immediately in the neighbourhood of the flagel-
lated chambers in the bath sponge, the granules becoming
more numerous in sponges in which the canal system
acquires a higher differentiation, till at length the collen-
cytes are concealed by them. According to this view,
sarcenchyme would appear to originate from a densely
granular collenchyme. Amoeboid wandering cells or arc/ue-
ocytes (fig. 22) are scattered through the matrix of the
collenchyme. They evidently serve very different purposes :
some appear to act as carriers of nourishment or as
scavengers of useless or irritant foreign matter ; others
may possibly contribute to the formation of higher tissues,
some certainly becoming converted into sexual products.
Their parentage and early history are unknown.

A tissue (cystencTiyme) which in some respects resembles certain
forms of vegetable parenchyme occurs in some sponges, particularly
Geodinidas and other Tetrad iiu'lliilo. It consists of closely ad-
jacent large oval cells, with thin well -defined walls and fluid
contents. Somewhere about the middle of the cell is the nucleus
with its nucleolus, supported by protoplasm, which extends from
it in fine threads to the inner side of the wall, where it spreads out
in a thin investing film (fig. 21 c). Cystenchyme very commonly
forms a layer just below the skin of some Gcodimdie, particularly of
Pacln/matisma, and, as on teasing the cortex of this sponge a large
number of refringent fluid globules immiscible with water are set
free, it is just possible that it is sometimes a fatty tissue, and if so
the contained oil must be soluble in alcohol, for alcoholic prepara-
tions show no trace of it. A tissue resembling cartilage, chondren-
ckymc, occurs in Corticidie (fig. 21 b).

Connective-tissue cells or desmacytes are present in most Desma
sponges ; they are usually long fusiform bodies, consisting cytes.
of a clear, colourless, often minutely fibrillated sheath,
surrounding a highly refringent axial fibre, which stains
deeply with reagents (fig. 21 d). In other cases the des-
macyte is simply a fusiform granular cell, with a nucleus
in the interior and a fibrillated appearance towards the
ends. The desmacytes are gathered together, their ends
overlapping, into fibrous strands or felted sheets, which in
the ectosome of some sponges may acquire a considerable
thickness, often constituting the greater part of the cortex.
The spicules of the sponge often furnish them with a sur-
face of attachment, especially in the Geoiliifid.v, where each
sterraster of the cortex is united to its neighbours by des-
macytes, in the manner shown in fig. 10.

Contractile fibre cells or myocytes occur in all the higher Myo-
npungL's. They appear to be of more than one kind. Host c ytes.
usually they are fine granular fusiform cells with long
filiform terminations, and with an enclosed nucleus and
nucleolus (fig. 21 e). In the majority of sponges both ex-
current and incurrent canals art- constricted at intervals

SPONGES

47

cytes.

by transverse diaphragms or vela, which contain myocytes
concentrically and sometimes radiatcly arranged. The
excessive development of myocytcs in such a velum gives
rise to muscular sphincters such as those which close the
chones of many corticate sponges, such as PachymatismoL.
In this spoimv, which occurs on the llritish shores, the
function of the oscular sphincters can be readily demon-
strated, since irritation of the margin of the oscule is
invariably followed after a short interval by a slow closure
of the sphincter.

(Supposed sense-cells or xstkucytes (fig. 22) were first
observed by Stewart and have since been described by
Von Lendenfeld (/.?). According to the latter, they are
spindle-shaped cells, O'Ol mm. long by 0'002 thick; the
distal end projects beyond the ectodermal epithelium in a
fine hair or palpocil ; the body is granular and contains a
large oval nucleus ; and the inner end is produced into
fine threads, which extend into the collenchyme and are
supposed though this is not proved to become con-
tinuous with large multiradiate collencytes, which Von
Lendenfeld regards as multipolar ganglion cells (fig. 22).

Proto-
plasmic
con-
tiuuity.

FIG. 22. Transverse section through the edge of a pore in Demh-iUa cavernosa,
Lfd. ; cells in the middle to the right, archsocytes ; fusiform cells on
each side of them, myocytes ; g, above and below these, with processes
terminating against the epithelium, gland cells ; fusiform cells terminating
against the epithelium at s, :t- sthacytes ; at their inner ends these are con-
tinuous with ganglion cells. After Von Lendenfeld ( x SOO).

More recently he has described an arrangement of these
cells curiously suggestive of a sense-organ. Numerous
sesthacytes are collected over a small area, and at their
inner ends pass into a granular mass of cells with well-
marked nuclei, but with boundaries not so evident ; these
he regards as ganglion cells. From the sides of the gan-
glion other slender fusiform cells, which Von Lendenfeld
regards as nerves, pass into the mesoderm, running tan-
gentially beneath the skin. The inner end of the ganglion
is in communication with a membrane formed of fusiform
cells which Von Lendenfeld regards as muscular. If his
observations and inferences are confirmed, it is obvious
that we have here a complete apparatus for the conversion
of external impressions into muscular movements.

In most sponges a direct connexion can be traced by
means of their branching processes between the collen-
cytes of the mesoderm and the cells of the ectodermal
and endodermal epithelium and the choanocytes of the
flagellated chambers. As the collencytes are also united
amongst themselves, they place the various histological
constituents of the sponge in true protoplasmic continuity.
Hence we may with considerable probability regard the
collencytes as furnishing a means for the transmission of
impulses : in other words, we may attribute to them a
rudimentary nervous function. In this case the modifica-
tion of some of the collencytes in communication with the
ectoderm might readily follow and special eesthacytes arise.
Fusiform collencytes perpendicular to the ectoderm, and
with one end touching it, are common in a variety of
sponges ; but it is difficult to trace the inner end into
connexion with the stellate collencytes, so that precisely in

those cases in which it -would be most interesting to find
such a connexion absolute proof of it is wanting.

The colour of sponges usually depends on tin; presence Pigment
of cells containini; granules of pigment ; though dispersed cclls -
generally through the mesoderm, these cclls are most richly
developed in the ectosome. Pigment granules also occur
in the choanocytes of some sponges, Oscaret/a lolmhiris
and Aplysina aerophoba, for instance. In the latter the
pigment undergoes a remarkable change of colour when
the sponge is exposed to the air, and finally fades away.
In many cases sponges borrow their colours from parasitic
alga: (Otcillatoria and Nostoc) with which they are infested
The colours of sponge-pigments are very various. They
have been examined by Krukenberg and Merejknovsky.
Zoonerythin, a red pigment of the lipochrome series, is one
of the most widely diffused ; it is regarded as having a
respiratory function. Reserve cells or thesoeytes (fig. 21 /)
have been described in several sponges as well as amylin
and oil-bearing cells.

Each spicule of a sponge originates in a single cell Sclero-
(fig. 21 h-n), within which it probably remains enclosed blasts,
until it has completed its full growth ; the cell then prob-
ably atrophies. During its growth the spicule slowly
passes from the interior to the exterior of the sponge, and
is finally (in at least some sponges, Geodia, Stelletta) cast
out as an effete product. The sponge is thus constantly
producing and disengaging spicules; and in this way we
may account for the extraordinary profusion of these struc-
tures in some modern marine deposits and in the ancient
stratified rocks. Within the latter these deciduous spicules
have furnished silica for the formation of flints, which have
been produced by a silicious replacement of carbonate of
lime (26).

The horny fibres of the Ceratosn are produced as a
secretion of cells known as sponginblasts, which surround
as a continuous mantle the sides of each growing fibre, and
cover in a thick cap each growing point (fig. 23). The

Fin. 23. Section through the horny fibre and associated tissues of a horny
sponge (Dcndrilla). A, longitudinal section ; s, layers of spongin, surrounded
at the sides by the lateral mantle of sponginhlasts, and at the ends by the
terminal cap. A desmachymatous sheath, a, surrounds the whole (x!50).
B, transverse section; in the centre is the soft core, surrounded by wavy

spongin layers, the outermost being surrounded by s] ginblssts, and these

by a fibrous sheath : i, part of an incurrent canal lined by llagt-lluti-il epi-
thelium ; e, part of an excurreut canal ; /, part of a flagellated chamber ( X 150).
After Von Lendenfeld.

lateral sponginblasts are elongated radially to the fibre ;
the terminal cells are polygonal and depressed. The latter
give rise to the soft granular core and the former to the
spongin- walls of the fibre. Cells similar to the lateral
sponginblasts, and regarded as homologous with them,
occur in a single layer just below the outer epithelium of
some horny sponges (Apfyxi/lit and DenJriUa), and under
certain circumstances secrete a large quantity of slimy
mucus (//).

48

SPONGES

Classification.

Class!- The phylum Parazoa or Spongix consists of two main
fication. branches, as follows :

Branch A. MEGAMASTIC- Branch B. MICROMASTIC-

TORA. TOR A.

Class CALCAKEA, Grant. Class I. MYXOSPOXGM:,

Order 1. llonwcaila, Pol. Haeckel.

Order 2. Heterocosla, Pol. Order 1. Halisardna.

Order 2. Chondrosiiui.

ClaSS II. SlLICISPONGLE.

Sub-class i. HEXACTINELLIDA,

0. Schmidt.

Order 1. Li/wciim, Zittel.
Order 2. Dic/i/uiiinn, Zittel.

Suh- class ii. DEMOSI'ONOI^E,

Sollas.
Tribe a. Monaxonida.

Order 1. Mi>iinj;n>ii.

Order 2. Ceratosa, Grant.

Tribe 1. Tetractinellida,

Marshall.

Order 1. Choristida, Sollas.
Order Z.Lithistida, O.S.

Position By the possession of both sexual elements and a complex histo-

in animal logical structure, and in the character of their embryological devel-

kingdom. opment, the sponges are clearly separated from the Protozoa ; on

the other hand, the choanoflagellate character of the endoderm,

which it retains in the flagellated chambers throughout the group

without a single exception, as clearly marks them off from the

JUctazoa. They may therefore be regarded as a separate phylum

derived from the choanoflagellate Infusoria, but pursuing for a

certain distance a course of development parallel with that of the

Mctazoa.

Different views have been propounded by other authors. Savile
Kent regards the sponges as Protozoa (10) ; Balfour suggested that
they branched off from the Metazoau phylum at a point below the
Ccelcntera, and considered them as intermediate between Protozoa
and Mctazoa ; Schulze regards them as derived from a simple
ancestral form of Ccelcntera (23) ; Marshall advocates the view that
they are degraded forms derived from Ccelenterates which were
already in possession of tentacles and mesenteric pouches (14).
Subdivi- As a phylum the Spongiie are certainly divisible into two branches,
siou in one including the Calcarea and the other the remaining sponges,
groups, which Yosmaer has termed Non- Calearca, and others Plethospongise.
Since, however, the choanocytes of the Calearca are usually, if not
universally, larger than those of other sponges, we may make use
of this difference in our nomenclature, and distinguish one branch
as the Megamastictora (fiaffriKTup, "scourger") and the other as
the Micromastictora.

Branch A. MEGA MA STIC'TORA .

Sponges in which the ehoanocytes are of comparatively large
size, 0'005 to 0'009 mm. in diameter (Haeckel, 6).

Class CALCAREA.

Calcarea. Megamastictora in which the skeleton is composed of calcareous
spicules.

Order 1. HOMOCCELA. Calcarea in which the endoderm consists
wholly of choanocytes. Examples : Lcucosolcnia, Bwk. ; Homo-
derma, Lfd.

Order 2. HETEKOCCSLA. Calcarea in which the endoderm is dif-
ferentiated into pinnacocytes, which line the paragastric cavity
and excurrent canals, and choanocytes, which are restricted to special
recesses (radial tubes or flagellated chambers). Examples : Si/con,
0. S. ; Grantia, Fl. ; Leuconia, Bwk.

Branch B. MICROMASTICTORA.

(Non-Calcarca, Vosmaer ; riclltosjioniiiie, Sollas.) Sponges in
which the choauocytcs are comparatively small, O'OOS mm. in
diameter.

Class I. MYXOSPONGI5!.

Myxo- Micromastictora in which a skeleton or scleres are absent.

. Order 1. HAUSAIICIXA. Myxosponqies in which the canal system
is simple, with simple or branched Sycon or enrypylous Rhagon
chambers. An ectosome sometimes and a cortex always absent.
Examples: Halisarca, Duj.; Oscarella, Vosin. ; Bajnlus, Lfd.

Order 2. CHOXDROSIXA. .l/iMvw//ii//;//,r in which the canal
system is complicated, with diplodal Rhagon chambers and a
well-developed cortex. Example : Chondrosia, O.S.

The ffalifairciii't are evidently survivals from an ancient and
primitive type. The simplicity of the canal system is opposed to
the view that they are degraded forms ; we may therefore regard
the absence of scleres as a persistent primary and not a secondary
acquired character. They are as interesting, therefore, from out-

point of view (absence of scleres) as the Ascons are from another
(uudifferentiated endoderm). With the Chondrosina the case is
different ; they differ only from Chondrilla and its allies by the
absence of asters ; these differ only from the Tcthyidsz by the
absence of strougyloxeas ; and we may very reasonably assume that
in these three groups we have a series due to loss of characters, the
Chondrill& being reduced Tcthyidss and the Chondrosina reduced
Clumdrillss. Still, as Huxley has well remarked, " classification
should express not assumptions but facts " ; and therefore till we
are in possession of more direct evidence it will be well to exclude
the Chondrosina from the Silicisponcjix.

Class II. SmCISPONSI-E.

Micromaslidora possessing a skeleton or scleres which are not
calcareous.

Sub-class i. HEXACTINELLIDA.

Silicispongise characterized by sexradiate silicious spicules. Hexacti-
Canal system usually simple, with Sycou chambers. Sponge nellida.
differentiated into ecto-, choano-, and endo-some.

Order 1. LYSSACIXA. HcxactincUula in which the skeleton is
formed of separate spicules, or, if united, then by a subsequent not a
contemporaneous deposit of silica. Examples : Eiiplcdella, Owen ;
Asconcma, S. Kent ; Hyaloncma, Gray ; Rossclla, Crtr.

Order 2. DlCTTONlNA. Hexactincllida in which sexradiate
spicules are cemented together by a silicious deposit into a con-
tinuous network pan passu with their formation. Examples :
Ftimct, Bwk. ; Eurete, Marshall ; Aphrocallistcs, Gray ; Myliusia,
Gray ; Daclylocabix^ Stutchbury.

The Hexactinellida are a very sharply defined group, impressed
with marked archaic features. No other Silicisponyiie possess, so
far as is known, so simple a syconate canal system. The oldest
known fossil sponge is a member of the Lyssacina (7 and 24), viz.,
Protospongia, Salter, from the Menevian beds, Lower Cambrian,
St David's Head, Wales. The group is almost world-wide in distri-
bution, chiefly affecting deep water, from 100 to 300 fathoms, but
often extending into abyssal depths ; occasionally, however, though
rarely, it frequents shallow water (Cystispongia supcrstcs dredged off
Yucatan in 18 fathoms).

Sub-class ii. DEMOSPONGLSI.

SilicisponrjiK in which sexradiate spicules are absent. Demo-

Tribe a. MOXAXOXIDA. spongia

Dcmosjionyiie in which the skeleton consists either of silicious
spicules which are not quadriradiate, or of horny scleres or in-
cluded foreign bodies, or of one or more of these constituents ill
conjunction.

Order 1. MOXAXONA. The skeleton is characterized by either
uniaxial or polyaxial spicules. Examples : Amorpkina, 0. S.
("crumb of bread" sponge); Sponrjilla, Link, ("freshwater"
sponge) ; Chalina, Bwk. ; Trthija, Link.

Order 2. CEKATOSA. The skeleton consists of horny scleres
which never include "proper" spicules, or of introduced foreign
bodies, or of both these in conjunction. Examples : Darwinella,
F. Muller ; Euspongia, Broun (the " bath " sponge).

Tribe 5. TETRACTINELLIDA.

Demospongiss possessing quadriradiate or triame spicules or
Lithistid scleres (desmas).

Order 1. CHORISTIDA. Tetrad incllida with quadriradiate or
triajne spicules, which are never articulated together into a rigid
network. Examples: Tctilla, 0. S. ; Thenea, Gray ; Gcodia, Lmk. ;
Dcrcitus, Gray.

Order 2. LITHISTIDA. Tetrad incllida with branching scleres
(desmas), which may or may not be modified tetrad spicules, arti-
culated together to form a rigid skeleton. Tria>ne spicules may or
may not be present in addition. Examples: Thecmdla, Gray ; Coral-
Uslfn, O.S. ; Azorica, Crtr.; Vctulina, O.S.

This large sub-class embraces the great majority of existing sponges.
Its external boundaries are fairly well defined, its internal divisions
iiiurh less so, as its various orders and families pass into each other
at many points of contact. Although there does not appear to be
much resemblance between a Lithistid sponge, such as Thconclla,
a Monaxonid such as Amurjihina, and an ordinary "bath" sponge
(EuxiHiinjiii), yet between these extremes a long series of inter-
mediate forms exists, so nicely graduated as to render their dis-
ruption into groups by no means an easy task. If the delimitation
of orders is difficult, that of genera is often impossible, so that
they are reduced to assemblages depending on the tact or taste of
the author. Thus Polcjaeff states that with a single exception
" none of the genera of Ceratosa are separable by absolute charac-
ters." The chief spicules of Monaxona are uniaxial, often accom-
panied by characteristic microseleres. Although distinguished as a
group by the absence of quadriradiate or truene spicules, two ex-
ceptions are known in which these occur ( Triccntrion, Ehlers, and
Acarnus, Gray) ; these, however, present unusual characters which
suggest an independent origin. The canal system of Monaxona has
not yet been fully investigated ; it appears usually to follow the

SPONGES

49

(Mirypylous Rhagon typo, Imt the aphodal is not unknown. The
(.t-iiliixn. contain all sponges with a horny skeleton, except those
iu which the horny fibres are cored or spined with silicious spicules
secreted liy the sponge (" proper " spic-uk-s) ; these are arbitrarily
assigned to the .Mniiiij-iniii. There is convenience in this proceed-
ing, lor horny matter is widely disseminated throughout the Demo-
li/mnitia!, occurriug even in the Ltlhistidn, and it frequently serves
to cement the oxeate spicules of the Moniivuiin into a fibre, without
at the same time forming a preponderant part of the skeleton. It
would be wellnigh impossible to say where the line should be drawn

one
coin-

between a fibre composed of Bpicules cemented by spougin and
consisting of spongin with embedded spicules, while there is c
parativcly no difficulty in distinguishing between fibres containin^,
spicules and fibres devoid of them. That the distinction, however,
is entirely artificial is shown by the fact that, after spicules have
disappeared from the horny fibre, they may still persist in the
mesoderm ; thus Von Lendenfeld announces the discovery of micro-
scleres (eymba) in an Aplysillid sponge and of strongyles in a
Cocospongia, both horny sponges. (A form intermediate between
this Aplysillid and the Desmaddonidm would appear to be To;co-
chalinn, Ridley.) The Ccratosa frequently enclose sand, Fora-
mini/era, deciduous spicules of other sponges and of compound
Ascidiaus, and other foreign bodies within the horny fibres of their
skeleton ; they also sometimes attach this material, probably by a
secretion of spongin, to their outer surface, and thus invest them-
selves iu a thick protective crust; In some Ccratosa no other
skeleton than that provided by foreign enclosures is present. The
canal system is syconate or eurypylous in the simpler forms and
diplodal in the higher. The Mamaxonida make their earliest ap-
pearance in the Silurian rocks (Clfmacospongia, Hinde), and are
now found iu all seas at all depths. The only sponges inhabiting
fresh water belong to this group. The TctreuAincli ida adhere to
the Monaxonida at more than one point, and one of these groups
has probably been a fruitful parent to the other, but which is
offspring and which parent is still a subject for discussion. The
Choristida iu its simplest forms presents a eurypylous Rhagon
system, in the higher an aphodal system. It is in this group that
the most highly complex cortex is met with; in the Geodinidsc,
for instance, it consists usually of at least five distinct layers.
Thus, proceeding outwards, next to the choanosome is a layer of
thickly felted desmachyme, passing into collenchyme on its inner
face ; then follows a thick stratum of sterrasters united together
by desmacytes ; this is succeeded by a layer of cystenchyme or
other tissue of variable thickness ; external to this is a single layer
of small granular cells and associated dermal asters; and finally,
the surface is invested by a layer of pavement epithelium. The
Lithistida, like the Ccratosa, are possibly of polyphylitic origin ;
iu one group (Tdracladina) the articulated scleres are evidently
modified calthrops spicules (see fig. 14 c), and associated with them
are free triaenes, which support the dermis and resemble precisely
the tritenes of the Choristida. In another group (FJialidocrqrida)
the scleres are moulded on a Monaxonid base (see fig. 13 q-s) ; but,
associated with them, triivnes sometimes occur similar to those of
the Tctracladlna. Both these groups are in all probability derived
from the ClwristiJa, and a distinct passage can be traced from the
Tetracladose to the Rhabdocrepid group. In the Rhaldocrepida
we find forms without trirenes ; these may possibly be degenerate
forms. The third group of Lithistids is derived from the Rhabdo-
crepida, the Anomocladine desma being derivable from the Rhabdo-
crepid by a shortening of the main axis into a centrum. The
thick centrum, from which the arms, variable in number, ori-
ginate, is hollowed out by a cavity, which appears during life to
have been occupied by a large nucleus, like that of a scleroblast,
and it is quite conceivable that the scleroblast, which in the
Tetracladine Lithistids lies in an angle between the arms, may
have become enclosed in an overgrowth of silica, from which addi-
tional arms were produced. The constancy with which spicules
in other sponges maintain their independence is very striking.
When once a persistent character like this is disturbed, excessive
variability may be predicted, as in the Anomocladine scleres.

Classifi- The classification of the sponges into families is shown in the

cation in following scheme.

Class CALCAREA.
Order 1. HOMOCCELA, Pol.

Family 1. AsroxiME, Hk. Humoccela which are simple or com-
posite, but never develop radial tubes. Examples : Ascctla, Hk.
(fig. 1) ; Lcucosolenia, Bwk.

Family 2. HOMODERMID.E, Lfd. Homoccela with radial tubes.
Example : Hbmoderma, Lfd. (figs. 3, 4).

Order 2. HETEROCCELA, Pol.

Tribe a. tSTCONARlA. 1

The flagellated chambers are either radial tubes or cylindrical
sacs.

Family 1. SYCONID^. The radial tubes open directly into the
paragastiic cavity.

Sub-family a. Sycpnina. The radial tubes are free for their whole)
length, or at least, distally. Examples : Synttu, Hk.; Sycon, O.S.

Sub-family 1>. Uteina, Lfd. The radial tubes are simple :md
entirely united. The ec.tosome is differentiated from thrrlia-inosnme.
and sometimes develops into a cortex. Examples: Grantixnn, U'd. ;
Utc, O.S. (fig. 5); Sycortusa, Hk.; Ainplwriscus, Pol.
^ Sub-family c. Grantina, Lfd. The radial tubes are branched.
The incurrent canal system is consequently complicated. An ecto-
some is present. Examples : Grantia, Fl. ; Hdcropajma, Pol. (fig.
4); Anamaxilla, Pol.

Family 2. SYLLEIBID.E, Lfd. The choanosome is folded. The
flagellated chambers (which are partly rhagose in Vosmaeria)
communicate with the paragastric cavity by excurrent canals
Examples : Pofy'na, Lfd. (fig. 6) ; Vosmaeria, Lfd.

Family 3. TEICHONELLIOE, Carter. Composite Sylleibidee with
the oseules and pores occurring on different parts of the surface.
Example : Tcickonclla, Crtr.

Tribe i. tLEucoNARiA.

The canal system belongs to the eurypylous Rhagon type.

Family 1. LEUCONIM, Hk. The outer surface is not differentiated
into osculiferous and poriferous areas. Examples : Leucetta, Hk. ;
Leucaltis, Ilk.; Lcucortis, Hk.

Family 2. EILHARDID.E, Pol. Composite Lcuconaria, with the
outer surface differentiated into special osculiferous and poriferous
areas. Example : Eilhardia, Pol.

The arrangement adopted above is founded on Von Lendenfeld's
revision (ft) of the classification propounded by Polejaeff(/6), who
in a masterly survey has thrown an unexpected light on the struc-
ture and inter-relationships of a group which Haeckel has rendered
famous. It should not be overlooked that Vosmaer (j/) had pre-
viously explained the structure of the Leucones. However errone-
ous in detail, Haeckel's views are confirmed in their broad outlines,
and it was with true insight that he pronounced the Calcarca to
offer one of the most luminous expositions of the evolutional theory.
In this single group the development in general of the canal system
of the sponges is revealed from its starting-point in the simple
Ascon to its almost completed stage in the Leucon, with a complete-
ness that leaves little further to be hoped for, unless it be the re-
quisite physiological explanation.

Class MYXOSPONGI^E.
Order 1. HALISARCINA.

Family 1. HALISAKCIDJB, Lfd. The flagellated chambers are
syconate. Examples: HaUsarca, Dnj. (with branched chambers) ;
Bajalus, Lfd. (with simple chambers).

Family 2. OSCAKELLIDJB, Lfd. The flagellated chambers are
eurypylous and rhagose. Example : Oscardla, Vosm.

Order 2. CHONDROSINA.

Family 1. CHONDROSIID.E. With the characters of the order.
Example : Chondrosia, O.S.

Class SILICISPONGIJ3.

Sub-class I. HEXACTINELLIDA.

Order 1. +LYSSACINA.

Family 1. EupLECTELLiDiE. The spicules of the dermal mem-
brane are "daggers" (fig. 15 a). Examples : Euplectclla, Owen;
Holascus, E. Sch. ; Habrodictyum, W.T.

Family 2. ASCONEMATID^:. The dermal spicules are " pinnuli "
(fig. 15 b,c). Examples: Asamema, S. Kent; Sympagclla, O.S.;
Cauloph&us, Schulze.

Family 3. HYALONEMATIDJE. The dermal spicules are pinnuli
and amphidisks (fig. 15 d). Example : Hyaloncma, Gray.

Family 4. tRossELiM). The dermal spicules are gomphi, stauri
(fig. 15/), and oxeas. Examples: Rossella, Crtr.; CTdteromorpha,
Gray ; Aulochona, E. Sch.

Family 5. *RECEPTACULID^E, Hinde. The distal ray of the
dermal spicules is expanded horizontally into a polygonal plate.
Example : *Receptaculitea, Defr.

Order 2. tDlCTTONINA.
Sub-order 1. UXCIXITAPJA.
Uncinate spicules are present.

Tribe a. CLAVULAEIA.
Clavulue (fig. 16 c) are present.

Family 1. FABKBmoL Characters those of the tribe. Example :
Furi-ffi, Bwk.

Tribe b. SCOPULAKIA.

The dermal spicules are scopulariae (fig. 16 b).
Family 1. tEr/BETID^. Branched anastomosing tubes, or goblet-
shaped, with lateral outlets. Examples : Eunte, Marshall ; Peri-
phniyella, Marshall ; Lcfroyclla, Schulze.

Family 2. tMELLiTTONlD^:. Tubular or goblet-shaped, with
honeycomb-like walls. Example : Aphrocallistcs, Gray.

1 An * indicates that the group is only known in the fossil state, a t that it
is both recent and fossil.

G

50

SPONGES

Family 3. tCHOXELASMATiDa;. Flat or beaker-shaped ; straight
funnel-shaped canals perforating the wall perpendicularly and
opening laterally on each side. Example : Chonelasma, Schulze.

Family 4. tVoLVULiNiM;. Tubular, goblet-shaped, or massive ;
crooked canals more or less irregular in their course. Examples :
Volvulina, Schulze ; Ficldingia, S. Kent.

Family 5. SCLEROTHAMNID*. Arborescent body ; perforated at
the ends and sides by round narrow radiating canals. Example :
Sclerothamn us, Marshall.

Sub-order 2. INERMIA.

Dictyonina without uncinati, clavulte, or scopulariae.
Family 1. tMYLlusiD.E. Depressed cup-shaped; a complex
folding of the wall produces lateral excurrent tubes. Example :
Mylvusia, Gray.

_Family 2. tDACTYLOCALYCiDj:. Goblet -shaped or pateriform,
with a thick wall consisting of numerous parallel anastomosing
tubes, of uniform breadth, which terminate at the same level
within and without. Examples: Dactylocah/x,Gra.v; Sderonlccima
O.S. ; Margaritdla, O.S.

Family 3. tEuiiYjpLEOMATiD^;. Goblet-shaped or resembling
ear-shaped saucers ; the wall deeply folded longitudinally so as to
produce a number of dichotomously branched canals or covered-in
grooves. Example : Euryplegma, Schulze.

Family 4. tAuLOCYSTiM;. Of massive rounded form, with an
axial cavity ; wall consisting of a system of obscurely radiating
anastomosing tubes and intervening inter-canals ; both inter-canals
and the external terminations of the tubes are covered by a thin
membrane, which is perforated by slit -like openings over the
lumina of the tubes, and thus assumes a sieve -like character.
Examples : Aulocystis, Schulze ; Cysti<spongia, Roemer.

This arrangement of the Hexactincllida is taken from the latest
work on the subject, Schulze's Preliminary Report on the "Challen-
ger " Hexactincllida. The reference of fossil forms to the families
here instituted is rendered difficult by the disappearance of the
requisite "guiding" spicules in the process of mineralization. A
revision of the fossil families to bring them into harmony with the
recent has certainly been rendered necessary, but this is too large
a task to undertake in this place.

Sub-class II. DEMOSPONGI.E.
Tribe a. MONAXONIDA,
Order 1. MONAXONA.

Family 1. TETHYIDJE. Skeleton consisting of radiately arranged
strongyloxeas (except in the genus Chondrilla, which is without
megascleres) and large spherasters. The ectosome is a thick fibrous
cortex. Example: Tethya, Link. ; Chondrilla, O.S.

Family 2. POLYMASTIM. Skeleton consisting of styles radiately
arranged and cortical tylostyles. Tbe oscules in many cases open
at the ends of long papilla;. Examples : Polyinastia, Bwk. ; Theca-
phora, O.S. ; Trichostcmma, Sars.

Family 3. SUBERITID-E. Skeleton consisting of strongylate or
tylotate styles, arranged to form a felt. The flesh spicules when
present are usually mierorabds or spirasters. Examples : Subcrites.
Nardo ; C'liona, Grant ; Poterimi, Schlegel.

Family 4. DESMACIDOJUD.E. The flesh spicules are cymbas.
Examples : Espmlla, Vosm. ; Desmacidon, Bwk. ; Cladorhiza, Sars

Family 5. tHALlCHONDRiOE. The flesh spicules when present
are never cymbas. Examples : Ealkhondria, Fl. ; Rcnicra, O.S.
Chalina, Bwk. ; * Pharetrospuugia, Soil.

Family 6. ECTTONIDA The skeleton consists of fibres echinated
by projecting spicules. Examples : I'locamia, O.S. ; Ectyon. Gray
Clathria, O.S.

Family 7. tSpONOiLLiD^. EaliAondridss which are reproduced
both sexually and by statoblasts. Habitat freshwater. Examples :
SpongUla, Lmk. ; Ephydatia, Link. ; Parmula, Crtr. ; Patamolems.
Marshall. 1

The foregoing classification is purely provisional ; the group re-
quires a complete revision.

Order 2. CERATOSA.

Family 1. DARWINELIID.E. Canal system of the eurypylous
Rhagon type. Flagellated chambers, pouch-shaped, large ; the sur-
rounding collenchyme not granular. Horny fibres with a thick
core. Examples : DurwineUa, Fritz Miiller ; Aplysilla, F.E.S
lanthcUa, Gray.

Family 2. SPQNGEUM. Canal system as in the Darwincllidx,
but the flagellated chambers more or less spherical. Horny fibres
with a thin core, and usually containing foreign enclosures.
Examples : Vclinca, Vosm. ; Spongdia, Nardo ; Psammochui,,,
Marshall ; Psammopemma, Marshall.

Family 3. SI-ONOIDJE. Canal system aphodal. Chambers small
and spherical ; surrounding collenchyme granular. Fibres with a
thin core. Examples : Hfuspongia, Broun ; Casciitodcrma, Crtr.
Phyllosponyia, Ehlers.

1 Freshwater sponges without statoblasts are excluded from this family and
lelt rur distribution amongst allied marine genera.

Family 4. APLTSINID^. Canal system diplodal ; collenchyme
surrounding the flagellated chambers densely granular. Fibres
with a thick core. Examples : Luffaria, Duch. and Mich. ; Vcron-
rjia, Bwk. ; Aplysina, Nardo.

The species of sponge in common use are three, Euspongia
officinalis (Linn.), the fine Turkey or Levant sponge; E. zimocca
(O.S.}, the hard Zimocca sponge ; and Hippospongia cquina (O.S.),
the horse sponge or common bath sponge. The genus Euspongia
is distinguished by the regular development of the skeletal network
throughout the body, its narrow meshes, scarcely or not at all
visible to the naked eye, and the regular radiate arrangement of
its chief fibres. Hippospongia is distinguished by the thinness of
its fibres and the labyriuthic character of the choanosome beneath
the skin. As a consequence its chief fibres have no regular radiate
arrangement. The species of Euspongia are distinguished as fol-
lows. In E. officinalis the chief fibres are of different thicknesses,
irregularly swollen at intervals, without exception cored by sand
grains ; in E. simocea they are thinner, more regular, and almost
free from sand. In E. oj/kiualis, again, the uniting fibres are soft,
thin, and elastic ; whilst in E. simocea they are denser and thicker,
to which difference the latter sponge owes its characteristic hard-
ness. Finally, the skeleton of E. officinalis is of a lighter colour than
that of E. simocea. The common bath sponge (Hippospongia
equina) has almost always a thick cake-like form ; but its specific
characters are not yet further defined.

Tribe b. TETRACTINELLIDA.

Order 1. CHORISTIDA.
Sub-order 1. SIGMATOPHORA.
The microsclere is a sigmaspire.

Family 1. TETILLIDJL The characteristic megasclere is a pro-
triune. Canal system in the lower forms eurypylous, in the higher
aphodal. The ectosome in the simpler forms is a dermal membrane,
in the higher a highly differentiated cortex. Examples : Tetilla
O.S.; Craniclla, O.S. (fig. 21 h, I).

Family 2. SAMIDJE. The characteristic megasclere is an amphi-
tri^ne. Example : Samus, Gray.

Sub-order 2. ASTEROP30RA.
The microsclere is an aster.

Group 1. SPIKASTKOSA. A spiraster is usually present.
Family 1. THENEIM;, Carter. The flesh spicule is a spiraster.
Canal system eurypylous. Ectosome not differentiated to form a
cortex. Examples : Thcnea, Gray (fig. 21 a, /) ; Pcecillastra (Nor-
mania), Bwk.

Family 2. tPACHASTRELLiM. Canal system eurypylous in the
lower, aphodal in the higher forms. Examples : Plakortis, F.E.S.
Dereitus, Gray.

Group 2. EUASTROSA. Spirasters are absent.
Family 1. tSTELLETTiDJi. Canal system aphodal, but approach-
ing the eurypylous in the lower forms. The cortex chiefly consists
of collenchyme in the lower forms ; in the higher it is highly differ-
entiated. Example: Stcllctta, O.S. (fig. 11); Ancorina, O.S. ;
Alyriastra, Soil.

Family 2. TETHYID.E. Although this family has been placed
in the Manaxonida, this seems to be its more natural position.

Group 3. STERRASTROSA. A sterraster is present, usually in
addition to a simple aster.

Family 1. tGEODiNiDJE. The megascleres are partly trirenes.
Canal system always aphodal. Cortex highly differentiated. Ex-
amples : Gcodia, Lmk. (fig. 21 ?i.); Padiymatisma, Bwk. (fig. 21 c);
Cydonium, Miiller (fig. 10); Erylus, Gray.

Family 2. PLACOSPONGID.E. The megasclere is a tylostyle.
Tritenes are absent. Example : Placospongia, Gray.

Sub-order 3. MICROSCLEROPIIORA.
Microscleres only are present.

Family 1. PLAKINID.E, Schulze. Canal system very simple,
belonging to eurypylous Rhagon type. Characteristic spicules
candelabra. Examples: Plaldna, F.E.S. (fig. 26).

Family 2. CORTICIM. Canal system aphodal or diplodal.
Mesoderm a collenchyme crowded with oval granular cells; the
spicules either candelabra, amphitrirraes, or triienes irregularly
rMc ""~<" 1 ; " ; * Example: Cor/ieium, O.S. (figs. 9, 21 b).

dispersed in it.

Family 3. THROMBID.E. Canal system diplodal. Spicules tricho-
tria-nes. Example : Thrombus, Soil.

The Pachastrettidie or the Corticidae. are probably the families
from which the Tetracladine Lithistids have been derived. In the
Tr/illiiliE the characteristic microsclere may occasionally fail, but
there is never any difficulty in identifying the sponge in this case,
as the trifenes are of a very characteristic form : the arms of the
protriaenes are slender, simple, and directed very much forwards,
making a very large angle with the shaft. Microscleres, having the
form of little globules, are sometimes present with the sigmaspires.

Order 2. LITHISTIDA, O.S.
Sub-order 1. TETRACLADIXA, Zittel.
The desmas are modified calthrops spicules.

SPONGES

51

granules ; at first they exhibit lively amoeboid movements,
but later pass into a resting stage. The cavity of the
mesodenn within which they are situated becomes lined

Fia. 24. Spermatozoa. a-h, Development of spermatozoa in Sycarulra raph-
tmw, highly magnified ; *, mature spermatozoa. After Polejaeff(x792). j,

A sperm ball in lin-itrdla (u(n(iaris(x500) ; fc, an isolated mature spermatozoon.
After Schulze(xSOO).

by a layer of epithelium, which may not appear, how :ver,
till a late stage of segmentation. In Euspongia offia alis
the ova occur congregated in groups within the mesod rm,
thus presenting an early form of ovary. The spermatozoa,
which also develop from wandering amoeboid cells, are
minute bodies with an oval or pear-shaped head an-l a
long vibratile tail (fig. 24 I). Each amoeboid cell produces
a large number of spermatozoa, which occur in spkeiical
clusters or sperm-balls. The heads of the spermatozoa,
as in the Metazoa, are produced from the nucleus of the
mother-cell, the tails from the surrounding protopi sm.
The development in detail is upon two plans. In Grantia,

Family 1. TETRACLAmn/E. With the characters of the sub-
order. Examples: Tlicondla, Gray (fig. 21 k); .Dworfcnuw, Bocagc;
"SipJumia, rarkinsnn.

Sub-order 2. RHABDOCRKPIDA.

The desmas are of various forms, produced by the growth of silica
over a uniaxial spicule.

Family 1. MEGAMORINIP.!;. The desmas are comparatively
large. Trurnes, usually dichotri;i/ncs, help to support the ccto-
some. Microscleres usually spirastcrs. Examples : Corn/I 7.s-A\,
O.S. ; *Hyalotragos, Zittel; Lyidium, O.S. ; *Dorijdcrmin, Zittel.

Family 2. MICKOMORINID/E. The desmas are comparatively
small. Trionies and microscleres are both absent. Examples :
Azorica, Crtr. ; *TcrrutUiM, Zittel.

Sub-order 3. ANOMOCLADINA.

Desmas with a massive nucleated centrum, from which a variable
number of arms (zS) extend radiately (see fig. 12/). Examples:
Vctulina, 0. S. ; *Astylosponrjia, Roemer.

Reproduction and Embryology.
Fresh individuals arise by asexual gemmation, both

external and internal, by fission, and by true sexual repro-
duction.

Asexual Fission is probably one of the processes by which com-
multipli- pound sponges are produced from simple individuals,
cation. Artificial fission has been practised with success in the

cultivation of commercial sponges for the market. Ex-
ternal gemmation has been observed in Tlienna, Tethya,

Polymastia, and Oscarella. A mass of indifferent sponge-
cells accumulates at some point beneath the skin, bulges

out, drops off, and gives rise to a new individual. Internal

gemmation, which results in the formation of a statoblast,

is only known to occur in the freshwater Spongillidx,

The statoblasts consist of a mass of yolk -bearing

mesoderm cells, invested by a capsule, which in

Ephydatia fluviatilis is composed of an inner

cuticle of spongin separated from a similar outer

layer by an intermediate zone of amphidisks and

interspersed protoplasmic cells. On one side of

the capsule is a hilum which leads into the interior.
Their development has recently been studied by Giitte,

with results that confirm the conclusions of Carter (j)

and Lieberkiihn (fj). The process commences with an

accumulation of amoeboid cells within the mesoderm to

form a globular cluster ; yolk grannies develop within

them, especially in those that lie nearer the centre. The

external cells give rise to the investing capsule ; some

resemble sponginblasts and secrete the inner and outer

horny cuticle ; others give rise to the amphidisks and

interspersed cells of the middle layer. Under favourable

conditions the interior cells creep out through the pore

of the capsule, and form a spreading heap, which by

subsequent differentiation gives rise to a youug Spongilla.

Since the freshwater sponges can only be regarded as

modified descendants of ancient marine species (prob-
ably of the family Ifttlichondridse), we may consider the

internal gemmules, like the similar statoblasts of the

freshwater Poli/:oa, as special adaptations to a changed

mode of life. They appear primarily to serve a protective

purpose, ensuring the persistence of the race, since they

only appear in extreme climates on the approach of

drought, and in cold ones on the approach of winter.

As a secondary function they serve for the dispersal of

the species ; some are light enough to float down a

stream, but not too far, so that there is no danger of

their being carried to sea ; others, which are character-
ized by large air-chambers, are possibly distributed by

the wind.

Sexual Both sexual elements may be formed in the
repro- same individual, e.ff., Oscarella lobularis, Grantia
on. raphanus, and many others ; but even in herm-
aphrodites one or other element usually occurs to

excess in different individuals, SO that Some are F[G 25 _ Development of a calcareous sponge (Symndra raphanw). a, ovum ; 6, c, ovum seg-
predominantly male and Others predominantly mented,-&, as seen from above, c lateral view; rf blastosphere; f, ampl.il.lastula; /corn-
if: 7 J meneement nf the invagination of the flagellated cells of the amphiblastula ; </, gastrula

female, rolejaeff found Only one such male form attached by its oval face; h,j, young sponge (Ascon stagi-), ft, lateral vi-, j, as seen from

to 100 female forms in Grantia raphanus. In above - After Schuize.

Other sponges Beniera fertilis, Euspon,,i<i otfr.-itialisihe raphanus (/j) the nucleus of the mother-cell divides into two

,? . mi i (fi" 24 b) one of the resulting daughter nuclei undergoes no

sexes are distinct. The ova develop from archaeocytes or ^^ ^ but with a gmall ^^ of ri heral protop i asm

wandering amoeboid cells, which increase in size and ac- forms a "cover-cell" to the other or primitive sperm nucleus and its
quire a store of reserve nourishment in the form of yolk associated protoplasm. The sperm nucleus repeatedly divides, with-

52

SPONGES

out involving the surrounding protoplasm (fig. 24 c-f). The result-
ing nuclei at length cease to exhibit a nucleolus, and become directly
transformed into the heads of spermatozoa; the tails are appropriated
by each head from the common protoplasmic residue. The mother-
cell in this case undergoes no increase in volume as development
proceeds, and it is not enclosed within an " endothelial " layer. In
the second and apparently more usual case (20) no "cover-
cell " is formed, but the mother-cell divides and subdivides,
protoplasm as well as nuclei, till a vast number of minute
cells results ; the nucleus of each becomes the head of a
spermatozoon and the protoplasm its tail. In this case the
sperm-ball does increase in bulk : it grows as it develops,
and the cavity containing it becomes lined by epithelium,
or so-called "endothelium" (fig. 24/). No doubt (75) the
development of the epithelium stands in direct physiological
connexion with the growth of the sperm-ball.

Ccelenterate history as exemplified in the last two events will furnish
an explanation of the remarkable divergencies which distinguish
the two phyla. The history of the second or planula type has been
thoroughly worked out by Schulze (20) in a little incrusting Tetrac-
tinellid sponge (Plakina monolopha, Sclmlze). The ovum by regu-
lar segmentation produces a blastosphere, the blastomeres of which

^ *?t *

9&W*

-,is J tf^g^4S
8Sgpftfiss?asJ9:

Embryo- Obscure as are the details of this subject, suffi-
lo S7- cient is known to enable us to make out two chief

types of development. One, common amongst the

calcareous sponges, and possibly occurring in a single

genus (Gwnmina) of the Micromastictora, is char-
acterized by what is known as the " amphiblastula "

stage; the other, widely spread amongst the

Micromastictora (Seniera, Desmacidon, Eiispongia,

Spongelia, Aplysilla, Oscarella), is characterized by

a " planula " stage.

The first has been most thoroughly investigated in
Grantia raphanus by Schulze (20). The ovum by repeated
segmentation gives rise to a hollow vesicle, the wall of
which is formed by a single layer of cells blastosphere
(fig. 25 d). Eight cells at one pole of the blastosphere
now become differentiated from the rest ; they remain ^j
rounded in form, comparatively large, and become filled
with granules (stored nutriment), while the others, rapidly
multiplying by division, become small, clear, columnar,
and flagellated. By further change the embryo becomes
egg-shaped; the granular cells, now increased in number
to thirty-two, form the broader end, and the numerous ^
small flagellated cells the smaller end. Of the granular
cells sixteen are arranged in au equatorial girdle adjoin-
ing the flagellate cells. A blastosphere thus differen-
tiated into two halves composed of different cells is "
known as an amphiblastula. The amphiblastula (fig. 25 c]
now perforates the maternal tissue, and is borne along an i =
excurrent canal to the oscule, where it is discharged to FIG. 26. Development of a Dcmespmv}ia.(riaki,ia monoloplia). n, planula (the central part

the exterior and swims about in a whirling lively dance.
It then assumes a more spherical form, a change premoni-
tory of the next most remarkable phase of its career. In
this the flagellated layer becomes flattened, depressed, and
finally invaginated within the hemisphere of granular cells,
to the inner face of which it applies itself, thus entirely obliterating
the cleavage cavity, but by the same process originating another
(the invagination cavity) at its expense (fig. 25/). The two-layered
sac thus produced is a paragastrula ; its outer layer, known as the
epiblast, gives rise to the ectoderm, the inner layer or hypoblast to
the endoderm. The paragastrula next becomes somewhat beehive-
shaped, and the mouth of the paragastric cavity is diminished in
size by an ingrowth of the granular cells around its margin. The
larva now settles mouth downwards on some fixed object, and ex-
changes a free for a fixed and stationary existence (fig. 25 3). The
granular cells completely obliterate the original mouth, and grow
along their outer edge over the surface of attachment in irregular
pseudopodial processes, which secure the young sponge firmly to
its seat (fig. 25 h). The granular cells now become almost trans-
parent, owing to the exhaustion of the yolk granules, and allow
the hypoblast within to be readily seen ; a layer of jelly-like
material, the rudimentary mesoderm, is also to be discerned between
the two layers. The spicules then become visible ; slender oxeas
appear first, and afterwards tri- and quadra-radiate spicules. The
larva now elongates into a somewhat cylindrical form ; the distal
end flattens ; and an oscule opens in its midst. Pores open in the
walls ; the endodermal cells, which had temporarily lost their
flagella, reacquire them, at the same time extending the character-
istic collar. In this stage (fig. 25 h, j) the young sponge corresponds
to a true Ascon, no trace of radial tubes being visible ; but as they
characterize the parent sponge they must arise Inter, and thus we
have clear evidence through ontogeny of the development of a
Sycon sponge from an Ascon.

The three most striking features in the history of this larva are,
first, the amphiblastula stage ; next the invagination of the llagi'l-
late cells within the granular, instead of invagination in the reverse
order ; and third the attachment of the larva by the oral instead of
the aboral surface. Should Srhulze be corrsct in deriving the
sponges from the Cuilcntcra, it is probable that the reversal of the

should be shaded), b, Section through side of planula ; ec, flagellated cells ; ft, their
flagella ; col, crenoblast. c, Attached gastrula (the paragaster is formed by fission), d,
Section across the foregoing, e, Young sponge (Rhagon). /, Part of a section through
fully grown sponge ; the attached basal layer is the hypomere ; the spongomere is fnM.il
so as to produce incuirent and excurrent canals ; the canal system is eurypylous ; ov, ova
(a segmented ovum lies between two of them) ; bl, blastospheres. After Schulze.

increase in number by further subdivision till they become con-
verted into hyaline cylindrical flagellated cells (fig. 26/). Thus a
blastosphere is produced consisting wholly of similar flagellated cells.
It becomes egg-shaped, and, hitherto colourless, assumes a rose-red
tint, which is deepest over the smaller end. The larva (now a
planula, fig. 26 a, by the filling in of the central cavity) escapes from
the parent and swims aliout broad end foremost. In this stage
thin sections show that the cleavage cavity is obliterated, its place
being occupied by a mass of granular gelatinous material contain-
ing nuclei (fig. 26 b). In from one to three days after hatching the
larva becomes attached. It then spreads out into a convex mass,
and a cavity is produced within it by the splitting of the central
jelly (fig. 26 c, d ; compare Eucope and others amongst the Cceleu-
terates). This cavity becomes lined by short cylindrical cells (endo-
derm), while the flagellated cells of the exterior lose their flagella
and become converted into piiiiiaeorvtes (ectoderm). The gelatin-
ous material left between the two layers now formed acquires the
characters of true collenchyme and thus becomes the mesoderm.
The endoderm then sends off into the mesoderm, as buds, rounded
chambers, which communicate with the paragastric cavity by a
wide mouth and with the exterior by small pores (fig. 26 c). An
oscule is formed Inter, and the sponge enters upon the lihngon phase.
Subsequent foldings of the sponge-wall give rise to a very simple
canal system (fig. 26/). In addition to these two well-ascertained
modes of development others have been described which at present
appear aberrant. In Oscarella lobularis, O.S. (sf), a curious series
of early developmental changes results in the formation of an
irregular paragastrula, the walls of which become folded (while still
within the parent sponge) in a complex fashion, so as to produce a
form in which the ineurrent and excurrent canals appear to be
already sketched out before the flagellated chambers are diflcrenti-
atecl off. In Spougilla Gotte describes the ectoderm as becoming
entirely lost on the attachment of the larva, so that the future
sponge proceeds from the endoderm alone. As Hfmujilla, however,

SPONGES

53

Homo-

jilasy.

Physio-
logy-

is a freshwater form, anomalies in its development (which remind
us of those in the development of the freshwater Ilydm) might
almost lie expected.

Probably in no other single group is the doctrine of
homoplasy enunciated by Lankcstcr more tellingly illus-
trated than in the sponges. The independent develop-
ment of similar types of canal system in different groups,
sometimes within the limits of a single family, is a remark-
able fact. In the following table the sign x shows inde-
pendent evolution of similar types of canal system in
different groups:

Ascon.

Sycon.

Rb&gon.

Eury-
pylous.

Aphodal.

Diplodal

X

X
X

X
X
X
X

X
X
X

X
X

X

X
X

X
X

Order Jfulisarcina

X

Sub-order Microsclcro-
phora

Family I'dillida

In the gross anatomy of the canal system similar homo-
plasy obtains ; thus, to cite one case amongst many, a
peculiar type of canal system characteristic of Siphnnia
(Lithistid) occurs also inmploca(S.6xa,c.tm&]lid),Sckmidtia
(Monaxonid), and other apparently unrelated genera. The
development of a cortex has likewise taken place inde-
pendently, but on parallel lines, in the Syconidte, L< u-
conidfc, Monaxona, TetiUidx, and Slellettidx. Calcareous
and silicious spicules have evidently an independent his-
tory, and yet all the chief forms of the former are repeated
in the latter. Quite as remarkable is the similarity of
the independently evolved horny spicules of Din-ii'un-ll<t
aurea to the quadri- and sex-radiate silicious spicules. We
have now sufficient knowledge of the morphology and evolu-
tion of the sponge to furnish the physicist with data for an
explanation of the skeleton, at least in its main outlines.
The obvious conclusion from this is that variation does not
depend upon accident, but on the operation of physical
laws as mechanical in their action here as in the mineral
world. Another important consequence follows: if homo-
plasy i.e., the independent evolution of similar structures
is of such certain and quite common occurrence in the
case of the sponges, it is also to be looked for in other
groups, and polyphylitic origin, so far from being improb-
able, is as likely an occurrence as monophylitic origin.

Physiology and ^Etiology.

Under the head of "physiology" we have almost a
blank. At present we do not even know what cells of the
sponge are primarily concerned in the ingestion of food.
If a living sponge, such as Sponr/illa, be fed with carmine
for a few minutes, then immersed in dilute osmic acid, and
examined in thin sections, its flagellated chambers are
found to be all marked out as red circular patches, and a
closer investigation shows that the choanocytes, and they
alone, have ingested the carmine. In this way we con-
firm the earlier observations of Carter made by teasing
carmine -fed sponges. This might be thought to decide
the question ; but, though, it effectually disposes of Pole-
jaeff's argument that the choanoeytes do not ingest nutri-
ment because mechanical disadvantages (conceived a jn-iwi)
make it impossible, it has not proved a final solution. Yon
Lendenfekl, by feeding sponges such as Aji///i//ii. with
carmine for a longer interval a quarter of an hour finds
that amceboid cells crowd about the sides and particularly
the floor of the subdermal cavities, and are soon loaded
with carmine granules ; after a time they wander away to
the flagellated chambers and there cast out into the ex-
curreut canals the carmine they have absorbed, apparently

in an altered state. On the other hand, the choanocytes,
though they at first absorb the carmine, soon thrust it out,
:i|'|i.-irently in an unaltered state. Hence Von Lendenfeld
concludes that it is the epithelium of the subdermal cavities
which is charged with the function of ingestion, and that
the ama'boid cells subsequently digest and distribute it,
and finally cast out the worthless residues. There may be
much truth in this view, but it requires to be supported
by further evidence. (1) Sufficient proof is not adduced
to show that the carmine granules expelled from the amce-
boid cells are really more decomposed than those rejected
by the choanocytes. (2) There is at present no proof that
carmine is a food, or that if it is sponges will readily feed
upon it. In either case one would expect the amoeboid
cells to play tire part which they perform in other organisms
and to remove as soon as possible useless or irritant matter
from the surface which it encumbers ; at the same time
the choanocytes, not having found the food to their liking,
would naturally eject it. (3) If the choanocytes do not
ingest food, how does the Ascon feed, since in this sponge
all the pinnacocytes are external ? It is, however, a very
noticeable fact that, as the organization of a sponge
increases in complexity, the choanocytal layers become
reduced in volume relative to the whole bulk of the
individual ; and it is quite possible that as histological
differentiation proceeds it may be accompanied by physio-
logical differentiation which relieves the choanocytes to
some extent of the ingestive part of their labours.

The origin of the sponges is to be sought for among m\o-
the choanoflagellate Infusoria ; and Savile Kent has de- lo gJ'-
scribed a colonial form of this group which is suggestively
similar to a sponge. Its differences, however, are as
marked as its resemblances, and have been sufficiently
pointed out by Schulze (23). Kent has called this form
Protospongia, a name already made use of, and fortunately,
as the organism is not in any sense a true sponge ; the
present writer proposes, therefore, to call it Sarillia, in
honour of its discoverer. It consists of choanoflagellate
Infusoria (see PROTOZOA, vol. xix. p. 858, fig. XXL, 15),
half projecting from and half embedded in a structureless
jelly or blastema, within which other cells of an amceboid
character and reproductive function are immersed. Pro-
fessor Haddon arrives at the generalization that conjuga-
tion amongst the Protozoa always takes place between
individuals of the same order : flagellate cells conjugate
with flagellate, amceboid with amoeboid, but never with
flagellate ; while in true sexual reproduction the conjuga-
tion occurs between two individual cells in different stages
of their life cycle : a flagellate cell conjugates with a resting
amceboid cell. Now Sanllia would appear to be extremely
near such a true sexual process, since the simultaneous
coexistence of cells in two different stages of life and
within easy reach of each other a necessary preliminary,
one would think, to the union has already been brought
about. That coalescence between two different histological
elements should result in products similarly histologically
differentiated (compare amphiblastula stage of Calcarea)
has in it a certain fitness, which, however, has still to be
explained. The mode by which an organism like Rarilli<t
might become transformed into an Ascon cannot be sug-
gestively outlined with any satisfactory results till our
knowledge of the embryology of sponges is more advanced.
The minute characters of the flagellate cells of the amphi-
blastula and other sponge larvEe are still a subject for
research. They often possess a neck or collurn ; but the
existence of a frill or collar is disputed. Kent asserts
that it is present in several embryos which he figures ;
and Barrois makes the same assertion in respect to the
larva of Ofr<ll<i, and illustrates his description with a
figure. On the other hand, Schulze and Marshall both

54

SPONGES

deny its existence, and the former attributes Kent's
observations to error. One constant character they do
possess : they are provided with rlagella at some stage of
their existence, but never with cilia. Ciliated cells, in-
deed, are unknown amongst the sponges, and, when pinna-
cpcytes exceptionally acquire vibratile filaments, as in
Oscarella and other sponges, these are invariably flagella,
never cilia. An Ascon stage having been reached at some
point in the history of the sponges, the Sycon tubes and
Khagon chambers would arise from it by the active pro-
liferation of choanocytes about regularly distributed centres,
possibly as a result of generous feeding. Vosmaer recog-
nized as the physiological cause of Sycon an extension of
the choanocytal layer. Polejaeff, relying on Von Lenden-
fekl's experiments, which seem to prove that it is the
pinnacocytes and not the choanocytes which are concerned
in the ingestion of nutriment, argues that, as in Sycon
the pinnacocytal layer is increased relatively to the choano-
4 cytal, we have in this a' true explanation of the transition.
The existence of Homoderma, Lfcl., however, shows that
in the\ first stage there was not a replacement of choano-
cytes by pinnacocytes, but that this was a secondary
change, following the development of radial tubes, and
therefore cannot be relied upon to explain them. The
radial tubes having been formed by a proliferation of
choanocytal cells, the reduction of those. lining the para-
gastric cavity to pinnacocytes would follow in consequence
qf the poisonous character of the water delivered from the
radial tubes to the central cavity, since this water not
only parts with its dissolved oxygen to the choanocytes
it first encounters, but receives from them in exchange
urea, carbonic acid, and fascal residues. The development
of subdermal cavities is explicable on Von Lendenfeld's
hypothesis.

Distribution.

Distribu- Our knowledge of this subject is at present but frag-
tiou m rnentary ; we await fuller information in the remaining
reports on the sponges obtained by the " Challenger." The
sponges are widely distributed through existing seas, and
freshwater forms are found in the rivers and lakes of all
continents except Australia, and in numerous islands, in-
cluding New Zealand. Many genera and several species
are cosmopolitan, and so are most orders.

As instances of the same species occurring in widely remote
localities we take the following from Polejaeff : Si/con arclicum is
found at the Bermudas and in the Philippine Islands, as also are
Leuconia multiformis a-nd Leucilla uter ; Sycon raphaniis occurs at
Tristan da Cunha and. the Philippines ; Hctcropcgma nodus-gordii
and Leuconia dura at the Bermudas and Torres Straits. We do not
know, however, whether these species are isolated in their distribu-
tion or connected by intermediate localities. Of the Calcarea about
eighty-one species have been obtained from the Atlantic, twenty-
two from the Pacific, and twenty-two from the Indian Ocean ; but
these numbers no doubt depend largely on the extent to which the
several oceans have been investigated, for the largest number of
species has been found in the ocean nearest home. Schulze states
that the ffexattinellida brought home by the "Challenger" were
obtained at seventeen Atlantic stations, twenty-seven Pacific, and
nineteen in the South Seas.' In the last the number of species
was greatest, in the Atlantic least. They flourish best on a
bottom of diatomaceous mud. The Calcarea and Ccmtosa are
most abundant in shallow water and down to 40 fathoms, but
they descend to from 400 to 450 fathoms. The ff.'.i'.i<iini'!!ida are
most numerous over continental depths, i.e., 100 to 200 fathoms;
but they extend downwards to over 2500 fathoms and upwards
into shallow water (10 to 20 fathoms). The Li'lltintii/n are not such
deep-water forms as the HcxactincUida, being most numerous from
10 to 150 fathoms. Only one or two species have been dredged
from depths greater than 400 fathoms, and none from 1000 fathoms.
The Clwristida range from shallow water to abyssal depths. A
characteristic deep-sea Choristid genus is Tlicnm, Gray (= U'yrill?
Thompsonia, Wright ; Dorvillia, Kent). This is most frequently
dredged from depths of from 1000 to 2000 fathoms ; but it extends
to 2700 fathoms on the one hand and to 100 on the other,
in time. Until about 1876 one of the chief obstacles to the inter-

space ;

^relation of fossil sponges arose from a singular mineral
replacement which most of them have undergone, leading
to the substitution of calcite for the silica of which their
skeletons were originally composed. This change was de-
monstrated by Zittel (jj) and Sollas (24), and, though it
was at first pronounced impossible, owing to objections
founded on the chemical nature of silica, it has since be-
come generally recognized. These observers also showed
that the fossil sponges do not belong to extinct types, but
are assignable to existing orders. Zittel in addition sub-
jected large collections to a careful analysis and marshalled
them into order with remarkable success. Since then
several palaeontologists have worked at the subject, Pocta,
Dunikowski, and Hinde (/), who has published a Cata-
logue which is much more than a catalogue of the
sponges preserved in the British Museum. The result of
their labours is in general terms as follows. Fossil sponges
are chiefly such as from the coarseness or consistency of
their skeletons would be capable of preservation in a miner-
alized state. Thus the majority are Hexactinellida, chiefly
Dk-tyonina Tetractinellida, chiefly Lithistida ; and Cal-
carea, chiefly Leuconaria. Monaxonid sponges rarely occur;
the most ancient is Climacospongia, Hinde, found in Sil-
urian rocks. A very common Halichondroid sponge of this
group (Pharetrospongia strakani, Soil.) occurs in the Cam-
bridge greensand; it owes its preservation to the collection
of its small oxeate spicules into dense fibres. The Clwristida,
though not so common as the Lithistids, are commoner
than the Monaxonids, particularly in Mesozoic strata.

The distribution of fossil sponges in the stratified systems may
be summarized as follows. CALCAREA. Homoccela, none. Hetcro-
ccela, a Syconid, in the Jurassic system. Numerous Leuconaria
from the Devonian upwards. MYXOSPONGM!. None; not fitted
for preservation. HEXACTINELLIDA. Lyssacina, from the Lower
Cambrian upwards. Dictyonina, commencing in the Silurian ; most
numerous in the Mesozoic group ; still existing. MOXAXONIDA.
Moiiaxona, from the Silurian upwards. Ccratostt, none ; few are
fitted for preservation. TETRACTINELLIDA. Choristida, from the
Carboniferous upwards ; most numerous in the Cretaceous system.
Lithistida, from the Silurian upwards ; most numerous in the
Mesozoic group. In ancient times the Hexactinellids and Lithistids
seem not to have been so comparatively uncommon in shallow
water as they are at the present day. Thus, in the Lower Jurassic
strata of the south-west of England we find Dictyoniue Hexactinel-
lids, Lithistids, and Leuconarian Calcarea associated together in a
shelly breccia and in company with littoral shells, such as Patella
and Trochus. Several Palfeozoic Hexactinellids actually occur in a
fine-grained sandstone. Of the Chalk, which is the great mine of
fossil sponges, we must speak with caution, owing to the insufficient
evidence as to the depth at which it was deposited.

As shown by Protospongia, the phylum of the sponges was in
existence in very early Cambrian times, and probably much earlier.
Before the end of the Silurian period its main branches had spread
themselves out, and, developing fresh shoots since then, they have
extended to the present day. Of the offshoots none of higher value
than families are known to have become extinct, and of these
decayed branches there are very few. The existence in modern
seas of the Asconidse, which must surely have branched off very
near the base of the stem, is another curious instance of the per-
sistence of simple types, which would thus appear not to be so vastly
worse off in the struggle for existence than their more highly
organized descendants.

Biblloaraphti. A fairly complete list, "f works on sponges published before
1SS2 will be found in Vosinaer's article "Fcirifcni"," in Bronn's Klassen und
Onlnnngcn, vol. ii. D'Arcy Thompson's Catalogue of Papers on Piotozoa and
Ccdenterata, a still more complete list, extends to 1884.

The following is a list of works, including those referred to in the preceding
pages : (/) C. Barrois, Embryologtt tt. qn,l,i,,rs Sponges d. I. Miim-h?, I':iris, is7ii.
(?) Bowei-tank, .-I Monograph nf n,ilisli Spongiartre, vols. i.-iv., 1SU4-S2 (vol.
iv. is posthumous, edited by Dr Norman), (j) Carter, a series of papers in the
A a a. ii ail .W,i:i. KnI. His/., from 1847 to the present time (18ST). (./) J. Clark, On
tlif Bponeiffi ciliatn> a* Infusoria flngcllata, ISii.j. (5) Grant, Eilin. Pliil. Jmn-n.,
1S2.1. (6) Haeckel, jlfontwmplu il. Kiillcsi-lni'iimme, 1S71. (-) Ilindt, .4 I'ulii-

logutaftheSpongeainthe British Museum, 1883. (flld., "On Hie Li-iTjjui-nliHil.-it."
in Quart. Journ. Gcol. Snr., xl. 705, 1884. (0) Keller, "Stndien ii. Organisation
u. Entwickelung d. Chalinecn," in Ztschr. f. wiss. Zoo}., xxxiii., 1S79. (10) Kent,
"Notes on the Embryology of the Sponges," in Ann. inul Mart. Nat. Hat.,
1S7S, ii. 139. (//) Von Lendenfeld, "On Aptmimtda," in Ztschr. f. wiss. Zool.,
xxxviii. (/?)Id., "A Monograph of Australian Sponges," in Proc. Linn. Snc.,N.S.
JlWra, vols. ix., x. (other papers by Von Lendenfeld will lie found under this

and Spermatogenesis in Sycandra raphanus," in Site. -Her. Acad. wiss. Zool.,

SPONGES

55

rf. Uniffniti'il f7m.-. (16) Id., "Ctinjlftiyrr" fif]inrt mi tlir Calcnrea, 188.1.
(/?) hi., Ditto on the Ctfratasa, lss-i. (/^) KMl-y, ^ r//. /NM/. r ( i//n7M> M/ //*,

".-Ifrrt," 1SS4. (/a) Schmi.lt, N,i-in;|.'s M/ ,,' .I,/',-,, i/,',. ,s.,i, 1M1-J, with Suplilr-

iiinit, i in iM'i-i.aml supplnii.'iii _ in ix>;r, ; Spongu of On < oast "/ ALgltrs, l*iw;
Spongt-Fauna of the Allantii; Isro; Sjm,/,. ,./ M,. tiulf nf Mrrim, 1S79. (20)
K. K. Schulze, investigations into ihc stnu'tmv ami di'vlopinmt <>f spnnurs,
in Ztschr. f. wiss. Zool., " On llnli^ircn," vnl. xxviii., l<-77 ; " On -

xxix., 1S77; "On AlJiisinidir," xxx., 1S7X ; "On M.-ta rphusis of ftiinunlra

rajitianus," xxxi., 1S7S ; "on S^uu^/m," xxxii., ^7* ; "On .**["<, xri, I:,'," [ft.;
"On Ilin-iiiin and OligoctTOi," xxxiii., 1S70; "On J'luldniiln-," xxxiv., ISM);
"On Cortichtm candelabrum," xxxv., 1SS1. (if) III., "On Soft Parts of
Kni'leeteUa asperyin/i/n," in Trans. Roy. Soe. Etlin , xxix., 1SSO. (-V) ll.,
I'/, It /i/iiiiu-ii Iteport on the "Challenger" Ilexari inrllHa. (2?) Id., "on llir
Relationship of the Sponges to (he ChoanoJJwjflltiln," in St^.-7>Vr. d. k.-p/rn.^.
Ahul.f. viss. Z., Berlin, 1SS5, translated in Ann. n>l Mmj. Nnt. His!., iss.',.
(34) Sollas, "On Sfourcmemo, in Ann. and M<j. Nut. Hist., xix., 1877; "On
I'li'ii-etroftpongta," in Quart. Journ. Geol. Soc., xxxiii., 1877; "On )/>/>/","
ib.; "On Protosptmgia," (''., xxxvi., 1SSO. (25) Id., "The Sponjre-Fauna of
Norway," in Ann. nii.l Mny. Kat. Hist., 1SSO-S2. (26) Id., "The Flint-Nodules of
the Trimmingham Chalk," ili., vi., 1S79. (27) Id., " Development "f /Mi'*r/vu
hbltltirix," in {'itart. ./num. Mier. ,sv/., xxiv., 1N84. (^J) Id., " On I'etitlina and
the Aiini/nu'nii/i mi," in /'roc. .ft. /risk vtcarf., iv., 1885. (29) Id., "Physical
Characters of Bponge-Spicules," in Proc. R. Dub. Soc., 1885. 'jo) Vejdovsky,
"The I'VshwatiT Sponges of Bohemia," in Abh. d. k. Hnhm. Aland, d. Wlss., ser.
vi., vol. xii., 1SS3. (ji) Vosmai-r, f' Leurandra aspera (doctor's diss., Leyden,
1S80). (j^) Id., "On thr /'r -//M< n/c((;(/a?," in Notes from the Leyden Museum,
vol. ii. (jy) Sponges of the H'illem Barents Expedition, 1SS4. (?^) "Poriferje," in
Bronn's Klnssen und Onlnungen, vol. ii., 1SS2, and still in progress. Cy) Zittel,
studies of fossil sponges, in Abh. d. k. bayer. Akad^llejactindlidu, 1877;
Litltistida, 1S7S; Monaftinellida and Calwrea, 1878.

Commerce.

When the living matter is removed from a Ceratose
sponge a network of elastic horny fibres, the skeleton of
the animal, remains behind. This is the sponge of com-
merce. Of such sponges the softest, finest in texture, and
most valued is the Turkey or Levant sponge, Euspongia
officinalis, Lin. The other two varieties are the Hippo-
spnngia equina, O. Schmidt, and the Zimocca sponge,
Euspongia zimocca, O.S., which is not so soft as the others
Distribu- (see p. 423 above). All three species are found at from 2
tion. to 100 fathoms along the whole Mediterranean coast, includ-
ing its bays, gulfs, and islands, except the western half of
its northern shores as far as Venice and the Balearic Isles,
Corsica, Sardinia, and Sicily. Bath sponges occur around
the shores of the Bahamas, and less abundantly on the north
coast of Cuba. They are of several kinds, one not dis-
tinguishable from the fine Levant sponge ; others, the
"yellow" and "hardhead" varieties, resemble the Zimocca
sponge ; and of horse sponges there appear to be several
varieties, such as the " lamb's-wool " and the "velvet"
sponge (Hippospongia gossypina and //. meandriformis).
The fine bath sponge occurs on the shores of Australia
(Torres Straits, the west coast, and Port Phillip on the
south coast). A sponge eminently adapted for bathing
purposes (Coscinoilerma lanuginosum, Crtr. ; Euspongia
mathewsii, Lfd.), but not yet brought into the market,
occurs about the South Caroline Islands, where it is actu-
ally in use, and at Port Phillip in Australia. The fine
bath sponge occurs in the North Pacific, South Atlantic,
and Indian Oceans, so that its distribution is world-wide.
Fishing. The methods employed to get sponges from the bottom
of the sea, where they grow attached to rocks, stones, and
other objects, depend on the depths from which they are
to be brought. In comparatively shallow water they may
be loosened and hooked up by a harpoon ; at greater
depths, down to 30 or 40 fathoms, they are dived for; and
at depths of from 50 to 100 fathoms they are dredged
with a net. The method of harpooning was the earliest
practised, and is still carried on in probably its most
primitive form by the Dalmatian fishermen. Small boats
are used, manned by a single ^harpooner with a boy to
steer ; when, however, the expedition is to extend over
night the crew is doubled. The harpoon is a five-pronged
fork with a long wooden handle, and if this is not long
enough another harpoon is lashed on to it. The Greek
fishers use a large boat furnished with two or three smaller
ones, from which the actual harpooning is carried on ; the
crew numbers seven or eight. One of the chief difficulties
is to see the bottom distinctly through a troubled surface.
The Dalmatian fishers throw a smooth stone dipped in oil

a yard or so in front of the boat ; the stone scatters drops
of oil as it flies and so makes a smooth track for the " look-
out." The Greeks use a zinc-plate cylinder about I. 1 , feet
long and 1 foot wide, closed at the lower end by a plate of
glass, which is immersed below the surface of the si'a ; on
looking through this the bottom may be clearly seen even
in 30 fathoms. This plan is also adopted in the Bahamas,
where harpooning carried on after the Greek system gives
employment to over 5000 men and boys.

The primitive method of diving-with no other apparatus
than a slab of stone to serve as a sinker and a cord to
communicate with the surface is still practised in the
Mediterranean. The diver carries a net round his neck
to hold the sponges. On reaching the bottom he hastily
snatches up whatever spojige he sees. After staying down
as long as he is able an interval which varies from two
to at the most three minutes he tugs violently at the
cord and is rapidly drawn up. On entering the boat from
depths of 25 fathoms he quickly recovers from the effects
of his plunge after a few powerful respirations ; but after
working at depths of 30 to 40 fathoms or more he reaches
the surface in a swooning state. At the beginning of .the
season blood usually flows from the mouth and nose after a
descent ; this is regarded as a symptom of good condition ;
should it be wanting the diver will scarcely venture a second
plunge for the rest of the season. The work is severe, and
frequently the diver returns -empty -handed to the boat.
Diving is usually carried on in the summer months; in
winter it is too cold, at all events without a diving-dress.
The ordinary diver's dress with ^pumping apparatus is
largely used by the Greeks. The diving is carried on
from a ship manned by eight or nine men, including one,
or rarely two, divers. At a depth of from 10 to 15 fathoms
the diver can remain under for an hour, at greater depths
up to 20 fathoms only a few minutes ; the consequences of
a longer stay are palsy of the lower extremities, stricture,
and other complaints. Dredging is chiefly carried on along
the west coast of Asia Minor, principally in winter after
the autumn storms have torn up the seaweeds covering
the bottom. The mouth of the dredge is 6 yards wide
and 1 yard high ; the net is made of camel-hair cords of
the thickness of a finger, with meshes 4 inches square. It
is drawn along the bottom by a tow-line attached to the
bowsprit of a sailing vessel or hauled in from the shore.

Prompted by a suggestion made by Oscar Schmidt, that Cultiva-
sponges might be artificially propagated from cuttings, ti n -
the Italian Government supplied funds for experiments to
determine the feasibility of cultivating sponges as an in-
dustrial pursuit. A station was established on the island
of Lesina, off the Dalmatian coast, and experiments were
carried on there for six years (18G7-72) under the super-
intendence of Von Buccich. The results were on the whole
successful, but all expectations of creating a new source
of income for the sponge-fishers of Dalmatia were defeated
by the hostility of the fishers themselves.

The details of the method of sponge-farming as practised
by Von Buccich are briefly as follows. The selected speci-
mens, which should be obtained in as uninjured a state as
possible, are placed on a board moistened with sea water
and cut with a knife or fine saw into pieces about 1 inch
square, care being taken to preserve the outer skin as in-
tact as possible. The operation is best performed in winter,
as exposure to the air is then far less fatal than in summer.
The sponge cuttings are then trepanned and skewered on
bamboo rods ; the rods, each bearing three cuttings, are
secured in an upright position between two parallel boards,
which are then sunk to the bottom of the sea and weighted
with stones. In choosing a spot for the sponge-farm the
mouths of rivers and proximity to submarine springs must
be avoided ; mud in this case, as in that of reef-building

SPONGES

Prepara-
tion for
market.

corals, is fatal. A favourable situation is a sheltered bay
with a rocky bottom overgrown with green seaweed and
freshened by gentle waves and currents. So favoured,
the cuttings grow to a sponge two or three times their
original size in one year, and at the end of five to seven
years are large enough for the market. Similar experi-
ments with similar results have more recently been carried
on in Florida. The chief drawback to successful sponge-
farming would appear to be the long interval which the
cultivator has to wait for his first crop.

After the sponge has been taken from the sea, it is
exposed to the air till signs of decomposition set in, and
then without delay either beaten with a thick stick or
trodden by the feet in a stream of flowing water till the
skin and other soft tissues are completely removed. If
this process is postponed for only a few hours after the
sponge has been exposed a whole day to the air it is almost
impossible to completely purify it. After cleaning it is
hung up in the air to dry, and then with others finally
pressed into bales. If not completely dried before pack-
ing the sponges " heat," orange yellow spots appearing on
the parts attacked. The only remedy for this is to unpack
the bale and remove the affected sponges. The orange-
coloured spots produced by this "pest," or "cholera" as
the Levant fishermen term it, must not be confounded
with the brownish red colour which many sponges natu-
rally possess, especially near their base. The sponges on
reaching the wholesale houses are cut to a symmetrical
shape and further cleaned. The light-coloured sponges
often seen in chemists' shops have been bleached by
chemical means which impair their durability. Sponges
are sold by weight; sand is used as an "adulteration."

It is difficult to obtain recent statistics as to the extent
of the sponge trade ; the following tables gives a summary
of the sponges sold in Trieste, the great European sponge
market, in the year 1871 :

TABLE I.

Description of Sponge.

For Export.

Value in .

Mean price
per pound.

Horse spon ^e

60,000
20,000
20,000
2,000

6s.
6s.
14s.
Ss.

TABLE II.

Description cf Sponge.

For Home Consumption.

Value in .

Mean price
per pound.

4400
550
950

6s.
6s.
14s.

(W. J. S.)

HYDROZOA

HYDEOZOA form one of the three classes into
JL wliichthe Ccelentera nematophora (distinguished from
the Coelentera porifera, or Sponges) have been divided.
It results from observations made by Ernst Haeckel that
the Ctenophora should not be regarded as a class equi-

valent to the Hydrozoa and Actinozoa, nor as a subdivision
of the latter class, but that they must be considered as a
peculiar modification of the medusiform Hydrozoa (see
final paragraph). If this conclusion be accepted, it will
be necessary to divide the Hydrozoa into two primary

B

Scyphomedus.ns from the Deep Sea. (After Haeckel, Challenger Reports, vol. iv. 1882).

A. PeriphyUa mirabUis, Haeck., one of the Peromedusw, one-third the natural size, a, one of the four interradial tentaculocysts (sensoiy organs) sunk
between its lappets ; b, one of the sixteen subnulial coronal lobes. The twelve tentacles (four peiTadi.il, eight adradial) are M-en.

13. Perradial section through Lucernarui bathyphila, Haeck., nat. size, or, perradial gastral pouch ; 6, gastral axial cavity ; c, ovary (fouv); d, gash-al filaments;

e, peiTadial gastral pouch ; /, manubvium and mouth ; g, the bundles of tentacles (eight, adradial).
The eight principal tentacles (four perradial and four interradial) are not in this species converted into adhesive anchors as in L. auricula, hut arc

altogether suppressed.

groups or grades, for which the names Polypomorpha and
Ctenophora are proposed.

The Hydrozoa correspond to the Linnajan genera Hydra,
Tuljidaria, Sertularia, and Medusa. The name was applied
by Huxley in 1856 to a group corresponding to that termed
Hydromedmx by Vogt (1851) and Medusse. by Leuckart
(1853), and embracing the forms placed by Gegenbaur in
his Elements of C cm/par alive Anatomy (1878) in four classes,
viz., Hydromedmx, Calycozoa, Tliecomedusx, and Medusse.
Our knowledge of the structure and life-history of the
Hydrozoa, many of which, on account of their delicacy and
oceanic habits, are excessively difficult to obtain in a state
fit for investigation, has greatly extended within the last
five years. Whilst in the two decades preceding this period
the admirable researches of Huxley, Gegenbaur, Agassiz,
and Allman had brought to light and systematized a vast
mass of information with regard to these organisms, the
later observations of Glaus, the Hertwigs, Haeckel, and
Metschnikoff, have corrected, extended, and added to
their history, especially in respect of embryological and
histological detail. An epitome of the present condition
of our knowledge of the group is afforded by the subjoined
tabular classification of its families, orders, and sub-classes.

The definition and synonymy of the divisions recognized

will be entered into, after a sketch has been given of the
common structural features of typical Hydrozoa.

CLASS HYDROZOA.
Sub-Class I. Scyphomedusae (syn. Epliymmcdusw).

Examples,

f Lncernaria (fig. 19).
'( Halidystus.
< Craterolophus.
"i Manama.

Order 1. LUCEBSASIS.

Fam. 1. EleuthcrocarpMa 1 .

2. Cleistocarpidze

Order 2. DISCOMEDUS.E (Haeckel).
Sub-Order 1. Cubostoma'.
Fam. 1. Protcphyridse.

2. Nausitholdse Nausithoc.

,, 3. Ephyrellidaj.
,, 4. Atollidaj.
,, 5. Cyclorchida?.
Sub-Order 2. Semostoma;.

I Chrvsnnrn (fig. 24, l>).
Fum. 1. Pelagidffi i l' C ll K la.

, 2. Cyana?id!c Cyamra.

, 3. Sthenonidse SOienonte.

4. Aurclldn Aurelia (figs. 26-31).

Sub-Order 3. Rhizostomre.

Fain. 1. Tetragameliae

2. Monogamelia?

Order 3. COKOMEDCSJE (Haeckel).

Fam. 1. Charybdeidse

,, 2. liursarida 1 .
,, 3. Chiropsalmid.T.
UnkT 4. I'i;unMKi'rp.E (Hiieckel).
Fam. 1. Pcriphyllidje.
,, 2. Pericrj'pHdse.

Cephca.
C'nssidpcia.
Hhizostoma (fig. 24, n).
CiamlKSBa.

s. 20-2;i).

58

HYDROZOA

Sab-Class II. Hydromedusse.

Order 1. GrsiNOBLASiEA-A.

(Tubnlaria (fig. 35).

Fam. 1. Tubularidce ! Hybocodon.

( Curymorpha (fig. 34).

2. Pennaridai { Vorticlava

3. Eudendridas .

4. Cladonemidse .

( Bougainvillia (figs. 36, 37).
. -! Perigonium.
( Lizzia (fig. 44).
t Cladonema.
" ( Ciavatella.

I Garveia.
5. Bimeridas ...................... } stylactis.

G. Dicorynidaj .................. Dicorync (fig. 40).

( Sarsiadse (fig. 45).

7. Corynids .................... < Coryne.

( Syncoryne (figs. 41, 46).
I Hydractiuia (tig. 39).

8. Hydrachmd* ............... \ Podocovyne.

,,10-Hydnd* ........................

Order 2. CALTPTOBLASTI;A-LEPTOME|>I;S.

Fam.l.Pmmularid* ..................

{

/ Eucopidie.
3. Campanularid* j 5S*

4

4. Thauraantiadse

Laomedea.

Obelia.
Tlmumantias.
Lafoca.
Meliccrtum.
Tima.
jEquorea.
Zygodactyla.
_ Rhegmatodes.
Order 3. TRACHOMEDUS^: (Haeckel).

Fam. 1. rctasiche Petasus.

2. Trachynemidse Rhopalonema.

3. Aglauridse Aglaura.

5. .lEcuioridse

4. Geryonidse

{ carularina (figs. 48, 49).
Order 4. NARCOMEDCS^E (Haeckel).

Fam. 1. Cunanthidse .................. Cunina (figs 50,51).

,, 2. Peganthidie .................. Polyxenia.

Order 5. HYDROCORM.LINJE (Moseley).

Fam. 1. Milleporida: ................... Millepora (figs. 52, 53).

I Sporadopora.
2. Stylasteridse .................. \ Distichopora.

(Astylus (fig. 54).
Order 6. S:PHONOPHORA.

Sub-Order 1. Pliysophoridse.

Fam. 1. Athorybiadas ................. Athorybia.

2. Physophoridse ............... Physophora (fig. 57, C)

C l-'orskallia.
, 3. Agalmidffi ..................... < Halistemma.

(Agalma(fig 57. E)
4. Apolemiadfe .................. Apolemia.

5. lihizopliysidaj .............. Rhizopliysa.

Sub-Order 2. Physnlidoe.

Fam 1. Physalida? ..................... Physalia.

Sub-Order 3. Calycophoridse.

Fam. 1. Hippopodiido: ................ Gleba.

C Praya.
2.Dipbyidse ..................... 1. Dipllyes (fig. 57. A).

I Abyla.
3. Monophyidaj .................. Spliicvonectea.

Sub-Order 4. Discoidea;.

( Velella.
"

Fam. 1. Velelllds

.
"( Poipita.

The ITi/drosoa present a greater simplicity of ultimate
structure than do any animal organisms possessed of as
great a complexity of external form. As in all Metazoa or
Enterozoa, the life cycle of a hydrozoon starts with an egg
which is at first a single cell or unit of protoplasm, but
proceeds after fertilization to multiply by transverse fission
in such a way that the resulting cells or units are arranged
in two layers, each one cell deep, disposed around a central
cavity the enteron or archenteron. The sac thus formed
is known as a diblastula (figs. 1, 2, and 25). By the forma-
tion 1 of a mouth to the sac, the enteron acquires the functions
of a digestive retort in which food matters taken in at
the mouth are brought into a chemical condition suitable
for the nutrition of the surrounding cells. The two layers
of cells (of which the outer only acquires additional layers"

1 In Ili/ilivmedusec the inner layer of cells forms by delamiuation,
in Scyphomeduscc by imagination. In the latter case the sac closes
up, ami the mouth is formed by a new opening.

- It is probable that the numerous rows of cells described in the
eudoderm of Tuliuliifin and f.'uri/iiiiirjjha by Allman, in his great mono-
graph of the Tithularuin Ifydroicls, are due to a plication of the

by the division of the primary cells, and that by no
means in all cases) received from Allmau (Phil. Trans.,
1855) the names respectively of the
ectoderm and the endoderm, having
previously been shown by Huxley
(1849) to be the fundamental mem-
branous constituents of which the
most varied parts of the more com-
plex Hydrozoa such as tentacles,
swimming bells, and air-bladders
are built up in the adult condition.
Huxley also pointed out the iden-
tity of these membranes with the
two primary layers of the vertebrate

L, J , , j,i FIG. 1. Diagram of a Di-

embryo. The endoderm and the
ectoderm, which present themselves,
as is now known, in the diblastula (or

, , , r 11 ET .

gastrula) phase of all anterozoa, re-
main in//y<7co^oa(and also in the allied
groups of Ccflentera) as permanently distinguishable ele-
ments of structure. This important disposition is associ-
ated with and dependent on the simple character which the
archenteron or primitive digestive space retains. Into what-
ever lobes or processes the sac-like body may be, so to

blastula. a, orifice of in-
vagination (blastopore) ;
fr, aichenteric cavity ; c,
endoderm ; rf, ectoderm.
(From Gegenbaur's Ele-
ments of Comparative
Anatomy )

FIG. 2. Formation of trie Diblastnla of Ewape (one of the Calyptoblastic Hydro-
meduste) by delatnination. (From lialfour, after Kowalewsky.) A, B, C, three
successive stages. ep t ectoderm; hit, endoilerm; at, enteric cavity.

speak, moulded, whether tentacles 3 or broader expansions,
into these the cavity of the archenteron is extended in the
first instance; and where the actual cavity is obliterated
the endodermic cell-layer remains to represent it (Gefiiss-
platte or endoderm-lamella, see figs. 7 and 10).

Conversely, whatever canals or spaces are discovered in
the substance of a hydrozoon (excepting only the cavity of
ectodermal otocysts) are simple and direct continuations
of the one original enteric cavity of the diblastula, and all
such spaces are permanently in free communication with
one another. 4

The whole of the IIydro:oa seem to present a lower grade
of structure than the Adinozoa, in so far as the latter,
whilst retaining permanently free communication between
all parts of the archenteric space, yet exhibit a differentia-
tion of this space into an axial and a periaxial portion a
digestive tube and a body cavity. The differentiation has
only to proceed a step further, namely, to the closure or
shutting off of the axial from the periaxiul portion of
the archenteric space, and we obtain the condition which
characterizes the adult forms of the Ccelomata, or animals

original endodermal cell-layer. The two kinds of cells in two layers
figured by the same authority in the emloderm of Gfmmcllaria implexa,
pi. vii. tig. 5, cannot, however, be thus explained.

3 Some solid tentacles, with a single axial row of endodermal cells,
form au exception to this statrim-nt.

4 The observations of Eilhard Schulze cited in the article CCELENTEKA
do not form any real exception to this statement.

HYDROZOA

59

with blood-lymph space distinct from digestive canal. 1
With the attainment of the ccclomate condition, the two
fundamental cell-layers, ectoderm and endodenn, which still
appear in the embryo, become so far interwoven, and their
products so highly differentiated, that it is no longer possible
to recognize them as anatomical structures in the adult.

The only deep-seated distinction between Hydrozoa and
Antkozoa (the Actinozoa being thus termed when the
Cteiiopkora are detached from them) appears to be the
particular differentiation of the archenteric space iu Anthozoa
which has just been noted. It is no longer possible to
separate the two groups from one another as Exoarii and
Endoarli, as was proposed by Kapp ( Ueber die Polyptn im
Allyemeinen und die Aetinien insbesondere, Weimar, 1&29)
the first term indicating the Hydrozoa as possessed of
external generative organs, whilst by the latter term the
Anthozoa are pointed to as having internal generative
organs. 2 This distinction breaks down completely in the
case of Lucernaria, and even in that of the so-called phanero-
carpous and some other medusce which discharge their
genital products by the mouth, and quite rarely by rupture of
the outer body-wall. The tendency to form calcareous
deposits in the deep layers of the ectoderm, or mesoderm,
as it has been termed, exhibited almost universally by the
Anthozoa (whence the name Coralligena applied to them),
is distinctive of them, though it has been shown first by
Louis Agassiz, and more fully and recently by Moseley, to
be paralleled among Hydrozoa, by the external calcareous
deposits of the abundant and widely distributed Millepores
and Stylasterids. A minute distinction between Hydrozoa
and Anthozoa, which does not, however, hold good uni-
versally, is found in the form of the barbed threads ejected
by the nematocysts. Instead of the complicated forms
present in the latter group, the Hydrozoa are usually pro-
vided with either an unbarbed thread or one in which the
barbs are confined to three at the base and a few minute
barblets (fig. 5).

Fundamental Forms of the Hydrozoa. The diblastula
derived from the egg of a hydrozoon, when provided with
a mouth, may be spoken of (as are the equivalent forms
in other animals groups) as a person. Either this person
elongates and develops tentacles in a circlet around or near
the mouth, and usually becomes fixed by the aboral pole of
the sac-like body, or the sac gradually assumes the form
of a clapper-bell or of an umbrella with greatly thickened
handle, the mouth being placed at the free end of the handle
or of the clapper, and the animal freely swimming by the
contractions and expansions of the dome of the bell (disc
of the umbrella). The two forms of persons are known,
the former as the "hydriform" (2, 3 in fig. 16), the
latter as the " medusiform " (4, 5, 6 in fig. 16).

The HYDRIFORM PERSONS usually occur as fixed branching
colonies or trees (figs. 36 and 37) produced by lateral budding
from an original hydra-form developed from a diblastula.

The hydriform person in its most fully developed state
is seen in the colonies of T-ubularia. In such a colony a
number of hydriform persons are united like the flowers of
a plant on its branches (whence Allman's terms hyclranth,
hydrophyton). Each hydriform person (fig. 35) has an
elongated body with oral and aboral pole. The mouth is
placed centrally at the oral pole, which is souiewhat enlarged
and conical. At the apex of the cone, immediately around
the mouth, is a circlet of small tentacles ; at the base of
the cone is a second circlet of larger tentacles; the surface
of the oral cone is termed the hypostome. In other genera

1 The Enterozoa or Metazoa admit of division into two grades (1)
tlie Ccdentera, including sponges, polyps, jelly-fish, and corals, and
(2) the Cceloinata, including all remaining forms.

* See, however, note to the paragraph headed Definition of the
llijdro-.oa, p. 555.

(f.ff., Hydra, fig. 42) the smaller circle of tentacles is
wanting ; in others, again, the tentacles are irregularly
placed and not concentrated into one circlet (fig. 38).
We regard the former as the typical condition. In the
hydriform persons of the Scyphomedusce (figs. 20 and 27)
the vertical axis is much shortened, the hypostome is flat,
and the whole body cup-like or hemispherical

The tentacles of the hydriform person are sometimes
hollow (Hydra, Garveia nutans, Hydrocorallince), being
mere prolongations of the sac-like body ; but usually,
though the endodermal cell-layer is continued into them,
they are solid (2 in fig. 16). Very generally the tentacles
of the hydra-form are indefinite in number, but in those
belonging to the group of Scyphomedusae a primary series
indicating four radii (perradial) can be distinguished, to
which are added four intermediate to these, marking four
secondary radii (interraclial), whilst eight more placed
between the eight of the perradial and interradial series
are known as adradial tentacles. The surface of the hydra-
form may be entirely naked, or encased in a horny tube
(perisarc) formed by the ectoderm : this may be confined
to the aboral portion of the hydranth and to the common
stem which unites the persons of a colony, or it may rise
up and form a cup (or hydrotheca) around the oral region
of the hydranth (figs. 32 and 33).

The bodies of all hydriform persons, as well as the ten-
tacles, are excessively contractile, and when hydrothecse are
present can be withdrawn into them.

The ectoderm or outer cell-layer furnishes the protective
and contractile tissues of the hydra-form. Very usually
it is not more than one or
two cells deep, and is sepa-
rated from the eudoderni by
a structureless lamella of
firm consistence. In Hydra
large cells of the ectoderm
(neuro-muscular cells of
Kleinenberg) bound the
external surface (fig. 3) and give off horizontal muscular
processes which lie side by side on the structureless lamella
forming thus a deep muscular coat, the fibrous elements of

FIG. 3. Epidermo-muscular cells of Hydra.
m, muscular- fibre processes. (After
Klcinenberg, from Gegenbaur.)

FIG 4 Portion of the body-wall of Hydm, showing ectoderm cells above,
separated by " structureless lamella" from throe flagellate cndoderm cells
below The latter are vacunlated, and contain each a nucleus and several dark
granules In the middle ectoderm cell are seen a nucleus and three nemato-
cysts, with trigger hairs projecting beyond the cuticle. A large nematocyst,
with everted thread, is seen in the right-hand ectudennaJ cell. (After t. b.

Schulze.)

which are not independent cells. In larger species some of
the fibres may become separated from the tegumentary or
superficial cells, and acquire the character of independent
nucleated corpuscles (Hydractinia, Van Beneden). No
nervous elements nor sense-organs occur in any hydra-form
(except perhaps the Lucernarice). In Antmnularia some
ectoderm cells are amcebiform, and project processes which
change shape (nematophors). Tactile hairs (palpocils),

60

HYDROZOA

however, occur on the ectodermal cells, and the solid ten-
tacles are essentially tactile organs. Placed in and between
the large cells of the ecto-
derm (Hydra, Cordylophora,
Allman, Kleinenberg, F. E.
Schulze) are small nucleated
cells which become con-
verted into vesicles contain-
ing a three-barbed (figs. 4
and 5) or simple filament
(nematocysts). These are
frequently grouped on the
surface in wart-like pro-
cesses or " batteries." Ne-
matocysts also are found in
the endoderm; but it is prob-
able that their presence
there is due to their having
been swallowed.

The endoderm is usually
but one cell deep, and lines FIG. s. xematocyst of xgjra, showing

the entire Cavity of the body cell-substance and nucleus, cyst trig-
" * ger nuir, rtiiu evert uu tln'catl. (Alter

starting from the margin of r. E. sciraize.)
the mouth. In the region of the body proper, and in hollow
tentacles, the cells are ciliated (fig. 4). In this region they are
concerned in the secretion of digestive fluids and in absorp-
tion, and sometimes contain coloured granules (hepatic?). All-
man found in Myriothela (Phil. Trans., 1875) that the endo-
dsrni cells project processes
like the pseudopodia of Pro-
tozoa, and suggests that solid
food particles are incepted
by them. T. J. Parker has
published similar observa-
tion on Hydra (1880). In
the solid tentacles the en-
dodermal cells are greatly
modified, forming a kind
of skeletal tissue, each cell recalling by its vacuolation
and firm cell-wall the characters of vegetable parenchyma
(fig. 6). In the stems of Siphonophora endoderm cells give
origin to muscular processes like those of the ectoderm
(Glaus). This latter fact has a morphological significance
which cannot be too gravely estimated.

Generative products are not developed by any hydriform
persons (excepting the Lucernarice), the sexual process being
carried on by a distinct set of buds developed on the sides
of hydriform persons. These buds either become medusi-
form persons, or are degenerated representatives of such
persons (sporosacs) (figs. 17 and 18). Even the fresh- water
Hydra (fig. 42) does nmj appear to be an exception to this
generalization. The single egg-cell of Hydra projects at
the breeding season in an ectodermal covering, as a wart,
from the lower part of the body. A conical eminence or
two nearer the mouth contains the spermatozoa. Each
ovarium and each spermarium represents an aborted gene-
rative person. According to Kleinenberg the egg-cell and
the sperm-cells are both derived from the ectoderm. The
Lucernarice develop internal generative organs (fig. 19)
which correspond closely with those of the medusiform
persons of the group Scypkomedusce (see below), with which
they are classified. Both ova and testis are endodermal in
origin in Lueernaria and in the medusiform persons of the
Scyphomednsa', whilst they appear to be ectodermal in
origin in the complete medusiform persons of Hydro-
r/iedusce, though in the degenerate medusiform persons
known as sporosacs they may either or both have an
endodermal origin.

MEDUSIFORM PERSONS usually present themselves as
isolated free-swimming individuals, but like hydriform

FIG. 6. Vacuolated endoderm cells of carti-
laginous consistence from the axis of the
tentacle of a Medusa (Cunina). (From
Gegenbaur's Elements of Comparative
Anatomy.)

persons they have the power of producing new persons by
budding (figs. 44, 45, and 46), which may become detached
or may remain connected with the primary person (fig. 57)
to form a freely swimming colony (Siphonopkora) compar-
able to the fixed colonies of hydriform persons. Medusi-
form persons are often produced as the immediate result of
the development of the diblastula without any intermediate
hydriform phase (Pdagia among Scyphomedusce, Tracho-
medusce, Narcomeditsce, and probably som&Anihomeditsce and
Leptomedusix), but quite as frequently originate as lateral
buds upon the body-walls of hydriform persons (figs. 34,
37, and 43), or of other medusiform persons (see below), or
as metameric fission-products of hydra-forms. The typical
medusa-form is a hemispherical cup (the nectocalyx, or
umbrella, or disc), from the centre of which rises up a
cylindrical or conical process (the manubrium, erroneously
polypitf) at the summit of which is the mouth (4, 5 in fig.
16). Four perradial (see above for use of this term) ten-
tacle-like lobes very commonly surround the mouth, or
numerous small tentacles (fig. 58), whilst the margin of
the disc is beset with tentacles four in number, or a mul-
tiple of four (sometimes six, or one only, or indefinite).
Theaboral pole is dome-like, and is never attached except
in those forms which take their origin as buds on a hydri-
form colony when the connexion exists at this point. The
tentacles are, as in the hydriform persons, some solid, some
hollow : both occur in the same individual.

el

FIG. 7. Portions of sections through the disc of medusa?, the upper one of Lizzia,
the lower of Aurelia. el, endodmn lamella, or vascular lamella; jn, muscular
processes of the ectoderm cells in cross section ; rf, ectoderm ; e, endodenn
lining the enteric cavity; c, wandering endoderm cells of the gelatinous sub-
stance. (After Hertwig.)

The body is not so completely hollowed out as in the
hydriform persons. The mouth leads into a straight tube
(the stomach) which occupies the axis of the manubrium,
and expands at its insertion into the disc. The disc, even
when thick and fleshy, is not fully excavated by the enteric
cavity. In young forms the cavity does occupy it right up
to the margin, but gradually the lumen disappears (fig. 29),
leaving a series of canals and a continuous plate of endo-
derm (fig. 7) formed by the coalesced walls of the space (the
endodenn-lamella of the Hertwigs, see Organivmus der
Medmen, 1878; the vascular-lamella of Glaus, " Polypen
und Quallen der Adria," Wiener JDenhc/i., 1878). The
peripheral portion of the lumen of the original enteric cavity
forms the ring-canal, which runs all round the margin of
the disc, and is continued into the hollow tentacles. The
lumen is further retained at intervals in the form of radiat-
ing canals connecting the axial enteric cavity with the ring-
canal. These may be perradial, interradial, and adradial
(see above as to tentacles of hydra-form), and may branch
dichotomously in the disc or form networks.

The medusas are thicker and more fleshy to the touch
than are the hydra-forms, and are at the same time trans-
parent. This is entirely due to the enormous development
of a structureless substance between ectoderm and endoderm,
corresponding to the " Stlitz-lamella" or structureless lamella
of the hydra-forms. (See figs. 49 and 51, representing
sections of Carmarina and of Cunina.)

HYDROZOA

fil

The remarkable development of this substance in a hyaline con-
dition has led to the description of canals ami spares where none
exist the supposed spaees being really occupied by this hyaline
substance. F. E. Schulze's statements as to extra-enteric spaces in
Xni-!./ir are thus explained and more decidedly the supposed circular
and longitudinal canals attributed by some authors to the scyphi-
stoimi phase of I>i*ivninlusa:. In the same manner (according to
Clans) Allman's observations on StephanoseypMa are reconciled
with those of F. E. Schulze on Spotigicola clearly the same form.
Stephanoscyphua is devoid of either circular or longitudinal canals,
ami though it has four remarkable ridges on the enteric wall like
those of the scyphistoma of Scyphomedusce (see fig. 26) stands in all
probability very close indeed to the Tubularian genus, Perigonimus.

In a large number of medusa-forms the hyaline gelatinous
substance is structureless, but in many of the larger Scy-
phomedusce it is occupied by in- wandering amoeboid cells de-
rived from the endoderui and by fibrous trabecute (fig. 8).

Flo. 8. Gelatinous substance of the disc of Aurelia, showing a, fibrous tra-
beculffi, and b, wandering endoderm cells, with amoeboid movements. (From
Gegenbaur.)

The wandering endodermal cells are nutrient in function,
and represent so far isolated elements of the enteric canal
system.

The medusiform person is fundamentally adapted to
swimming movements. The muscular fibres are mostly
transversely striated, and are as a rule outgrowths of super-

FIG. 0. Muscular cells of medusrc (Li:zia). The uppermost is a purely muscular
cell fiom the sub-umbrella; the two lower are epidermo-musculur cells from
the base of a tentacle; the upstanding nucleated portion forms part of the
epidermal mosaic on the free surface of the body. (After Hertwig.)

ficial ectoderm cells as in Hydra (fig. 9), (though in some
cases distinct cells) ; they are confined to a sheet spread on
the oral face only of the disc or swimming-bell (sometimes
called sub-umbrella), to the extensile manubriurn and
tentacles, and to an inwardly directed flap of the margin uf
the disc known as the velum (Ve in 4 of fig. 16), which is
present in those medusae that are not flattened but conical
(bell-like). The muscular fibres on the oral face of the disc
and on the velum have a circular direction, interrupted
in some cases by radial tracts. The direction of the swim-
ming movements is obvious from this arrangement.

The velum is not a constant element in the medusa's
disc ; it serves to contract the space by which water is
expelled frurn beneath the bell in the act of swimming.

All fully-developed llt/dromedusce possess the velum, but
only a few of the Scypkomedwce (CharyMaia). In the
former the endoderm plate (vascular lamella) is not con-
tinued into it; in the latter vessels of the enteric system are
present in it (fig. 21), and, being probably morphologically
distinct, it has been here termed the "pseudo-velum."

Unlike the hydra-forms, the medusa-forms of Hydrozoa
possess iu addition to the tentacles highly-developed sense-
organs and gangliouic nerve-centres and nerves. The sense-
organs appear to be either eye-spots, or else otocysts, or
to combine the functions of both. In addition to these
are olfactory tracts or pits connected with the preceding.
The sense-organs are placed along the margin of the disc
(hence called marginal bodies), and are of three kinds:
(1) ocelli rounded pigment spots, rarely provided with a

Fig. 10. Fig. 11.

FIG. 10. Ocellusof amedusa (LiiziaKoellitert). oc, pigmentcd ectodermal cells;
/, lens. (After Hertwig.)

FIG. 11. Otocyst (formed entirely by ectoderm) of Phialidium, one of the
vesiculate mcdusce. rf l , superficial layer of ectoderm; d 2 , deep layer of ecto-
derm; fi, auditory cells of ectoderm; hh, auditory liairs; ?*/>, nerve body;
nr l , upper nerve-ring ; r, endoderm cells of the circular canal. The otolilh
cavity is seen above h.

\vas(Lizzia) (fig. 10), always placed at the base of a tentacle
or in the radius of one on the oral surface (Lizzia), entirely
ectodermal in origin ; (2) vesiculi or otocysts formed (as
discovered by the Hertwigs, 1878) by an invagination of the
ectoderm (fig. 11) containing concretions and hair cells;
either open or entirely closed, generally numerous, and
placed between tentacles, sometimes at the bases of tentacles
(Obelia) ; (3) tentaculocysts which are reduced and modi-
fied tentacles; into them alone of the three kinds of mar-

ginal bodies do the endoderm and, in the more complex,
the enteric canal system enter (figs. 12, 13, and 30). The
endodermal sac forms the axis of the tentaculocyst, its cells
secrete crystalline concretions, and it functions as an otocyst;
pigment spots, which may have cornea, lens, and retina
well developed, are formed sometimes to the number of
six (Charybdtea) on the ectoderm of the tentaculocyst (fig.
13). The olfactory sense-epithelium (fig. 14) is either dis-
tributed in a continuous band on the margin of the disc
(Hydromedusas, discovered here by the Hertwigs), or it 1

62

HYDROZOA

confined to deep pits (fovese nervosee) from each of which
a tentaculocyst arises (discovered in the Scyphomedusce in-
dependently by Schafer and Claus). With some exceptions,
medusae provided with ocelli are destitute of vesiculi, which
alone occur in the vesiculate Leptomedusce. Tentaculocysts

Fig. 13.

Fio. 13. Tentacnlocysts of medusae (^4, of Pelagia ; B, at Clianibdrea).
a, the free tentacle hanging in the notch of the disc; &, stalk; c, enteric
canal continued into it; d, enlarged portion of the canal; e, concretions
on endodermal cells; /, pigmented ectoderm ; g, lens. (From Gegenbaur.)

FIG, 14. Cells from the olfactory pits (foveiE nervosffi)of ^wre/m. (After Schafer.)

characterize to the exclusion of the ocelli and vesiculi the
Trachomedusce and Narcomedusce among Hydromedusce and
all the Scyphomedusce, except Lucernaria, where they are
replaced by '' colleto-cystophors."

The nervous system has only recently been correctly
recognized in medusse, though seen by Agassiz as long ago
as 1849, and described both by Fritz Miiller and Haeckel
in certain forms (Geryonidw) more recently (1860). It
differs remarkably in the two great groups into which the
ITydrozoa are divisible. In the Scyphomedusce there is
no continuous nerve-centre, but around and about each
tentaculocyst nerve-fibres and cells are grouped in such a
way as to divide the disc into zones of nerve supply corre-
sponding to the number of tentaculocysts (usually eight).

FIG. 15. Scattered nerve ganglion cells, c, from the sub-umbrella of Aurelia
aurita. (After Schafer.)

Both the Hertwigs (Nerven-System der Mcduscn, 1878) and
Eirner (Die Medusen, 1879) entirely missed in their re-
searches the large nerve-fibres and prominent ganglion cells
(fig. 15) which were discovered by Professor Schafer of
University College, London (Phil. Trans., 1879), in the
Scyphomedusce. The writer can confirm Schiifer's observa-
tion of the existence of such fibres and ganglion cells in
the region of the circular muscular zone on the oral face
of the disc of Aure/in, immediately beneath the flattened
epithelium of the ectoderm. Professor Claus of Vienna
has independently described (" Polypen und Quallen der
Adria," 1878) similar nerve-cells and fibres in Ghry-
saora and Charybdcea. Professor Schafer failed to ascer-
tain satisfactorily the origin and termination of the fibres,
which appear, however, to originate in superficial ecto-

dermal cells ("sense-epithelium") in the neighbourhood
of the tentaculocysts and in the cells of those organs,
and to terminate without any plexiform connexion with
one another in the muscular fibres. Eimer has described
very abundant and excessively fine fibres, often moniliform,
which extend from epithelial cells in the neighbourhood of
tentaculocysts and form a network traversing the gelatinous
substance of the disc in every direction. This observation,
though supported by the fact that such fibres ars indi-
cated by the extended experimental investigation of Eimer
and of Eomanes (Eimer, Die Medusen ; Komanes, Phil.
Trans., 1876, et seq.), is not confirmed by other observers,
and the fibres described are regarded as skeletal tissue. If
Einier's fibres do not exist, the muscular tissue of the
medusas must be regarded as acting to a large extent inde-
pendently of nerve-control; and this is borne out by Claus's
observation of the absence of sense-organs and nerve-fibres
from the swimming-bells of the Siphonophora (compound
medusse). In the Hydromedusce the nerve ganglion cells
arc grouped in a continuous ring around the margin of the
disc, separated horizontally into an inferior and superior
portion by the insertion of the velum. The difference in
the form of the nervous system has led Eimer to propose
the names Cycloneura for the Hydromedusae and Toponeura
for the Scyphomedusce. Amongst the latter, however,
Charybdcea, having a continuous velum like ffydromedusce,
has also a continuous nerve-ring.

Comparison and delations of Ilyclriform and Medusiform
Persons. A simple shortening of the vertical axis, and a
widening of the hypostome, with obliteration of the lumen
(but not of the cells) of the endoderm over a considerable
region of the disc thus produced, suffice to convert the hydra-
form into the medusa-form. 1 This change of proportion
made (fig. 16), the sense-organs of the medusiform person
have to be added, and the change is complete. Thus it be-
comes clear that we have to deal with one fundamental form,
appearing in a lower, fixed, nutritive phase and a higher,
locomotor, generative phase in the two cases respectively.

The phylogeny of the Hydrozoa and the historical relation-
ship of the two phases (hydriform and medusiform) appears
to be as follows.

A two-cell-layered sac-like form, with mouth and with or
without tentacles, was the common ancestor of Hydrozoa,
Anthozoa, and Sponges. The particular form which the
proximate ancestor of the Hydrozoa took (1 in fig. 16) is
most nearly exhibited at the present day in Lucernaria
and in the scyphistoma larva (hydra-tuba) of Discomedusce.
It was a hemispherical cup-like polyp with tentacles in
multiples of four, with four lobes to the wide enteric
chamber. This polyp, after passing a portion of its life fixed
by the aboral pole, loosened itself and swam freely by the
contractions of the circular muscular fibres of its hypostome
(sub-umbrella), and developed its ovaria and spermaria on
the inner walls of the enteric chamber. This ancestor
possessed, like its descendants, a very marked power of
multiplication, either by buds or by detached fragments of
its body. Accordingly it acquired definitely the character
of multiplying by bud-formation during the earlier period
of its life ; each of the buds so formed completed in the
course of time its growth into a free swimming person.
We must suppose that the peculiarities of the two phases
of development became more and more distinctly developed,
the earlier budding phase exhibiting a more elongated form
and simple enteric cavity (hydra-form), which subsequently

1 Tliis relationship, demonstrated by the Hertwigs' discovery of the
cndiidiTtn layer of the medusa's disc, differs from that supposed to
obtain by Professor Allman. He supposed the medusa's disc to
represent the coalesced tentacles of a hydra-form, and cited the webbed
tentacles of Laomcdca Jlcxuosa in support of the identification, which
had at the time very much to commend it.

HYDROZOA

63

became changed in the course of the ontogeny (develop-
ment of the individual) into the umbrella or disc-like
form, with coalesced enteric walls and radial and circular
surviving spaces (medusa-form). And now the ancestry
took two distinct lines, which have given rise respectively
to the two great groups into which the IIi/<lrn:na. are divi-
sible the ScyphomedwscB and the I/i/</>'iiK'<liniit. In the
one set the hydriform persons of a colony, instead of each
becoming metamorphosed into a medusiform person, pro-
ceeded each to break up into a series of transverse divisions ;
each division became a medusiform person, and was
liberated in its turn as a free swimming organism (figs.
26 and 27). We must suppose that this process began
historically by the outgrowth of new tentacles around the
point where the disc of a person fully transformed from the

'

Ge

FIG. 16. Diagrams to exhibit the plan of structure of hydriform and mednsiform
persons (all except 5 are vertical sections). A, base of tentacles, margin of the
di?c; B, oral margin; J/a, manubiium; Te, tentacle; CV, circular vessel;
EnL, endoderm lamella; ot, otocyst; or, ocellus off, olfactory pit; //, hood of
tentaculocyst; nnj, genitalia developing in mimubrium; dfj, genitalia develop-
ing in the disc (wall of a radiating canal) ; QP, sub-genital pits of the sub-
umbrcllii; Ol'\ gastra) filaments; IV, velum. 1, Form intermediate between
medusa-form and hydra-form. 2, Hydra-form with wide disc, matmbrium,
and solid tentacles (Tiibularian). 3, Hydra-form with narrower disc, and
hollow tentacles (Hydra). 4, Medusa-form with endodcrm lamella on the
left, the section passing through a radiating canal on the right; a velum, two
possible positions of the genitalia, and two kinds of sense-organs are shown
(ffydromedtutE). 5, A similar medusa-form seen from the surface. G, Section
of Aitrc/iii inifita, to show especially the nature of the sub-genital pits, (77 J ,
outside the genital frills, and the position of the gastral filaments GF, as well
as the flattened form of the disc.

hydriform to the medusiform phase was loosened in its
attachment and about to separate from the colony. The
" hastening of events," a well-known feature of organic
growth-sequences, would complete the development of the
newly sprouting person before the loosened medusa had
got well away, and so on with a third, fourth, and even
with twenty such successive buds. The separation of the
adult form from its fixed larva by fission has been justly
compared by Louis Agassiz to the separation of the
Comatula from its pentacriuoid larval stalk. If the stalk
could only produce new Comatula', the analogy would be
complete, Lttcernariais in the same way comparable with
the stalked crinoids, being an adult form which retains the
characters exhibited by the immature phases of its congeners.
The Scyphqmedusce do not, however, all exhibit a
hydriform phase, and a production of medusa- by the

"strobilation" or " metamerizing" of a scyphistoma.
Some of them (Pelayia) " hasten events " so far that the
diblastula never fixes itself, but becomes at once a single
medusa, the hydriform phase of the ontogeny being alto-
gether omitted. Certain peculiarities of the medusa's struc-
ture, above all the possession of gastral filaments (solid
filaments like tentacles projecting in four interradial groups
near the genitalia into the enteric cavity), serve to unite
Pelagia, which has no larval stage, and Litcernaria (which
is always of intermediate character between hydra-form
and medusa-form) with the numerous species which develop
by the strobilation of hydriform larvse.

The second line of descent which has given rise to those
Ilydrozoa known as Hydromedusce not only acquired at
the start a different mode of producing medusiform persons,
but the medusiform persons acquired characters differing
from those of the Scyphomedwce in important (but not
fundamental) features. The larval stage in this series
developed the property of budding to a very great degree,
so as often to form fixed tree-like colonies of considerable
size. Then the transformation of the identical colony-
forming persons into free-swimming persons was finally and
definitively abandoned, and only a late-appearing set of buds
proceeded to complete the typical changes and to become
medusas. The earlier-produced buds were thus arrested
in development, and became specially modified for the
purposes of a fixed life as members of a colony. Thus
they acquired the elongate form and the sporadic position
of the tentacles which we see in some hydriform persons of
the Hydromedusce group (figs. 38 and 40), and were adapted
to nutrition solely (hence the term trophosome applied by
Allman to such colonies). The characters of the mature
generative person, with its power of detachment and free
locomotion, being confined to the later buds borne on the
sides of the hydriform persons or on special portions of the
colony, we find that the former became more and more
specialized as sexual medusiform persons in proportion as
the latter became specialized as asexual hydriform persons,
and thus it is that we have the remarkable phenomenon of
hydriform colonies, developed from the eggs of medusae,
producing as it were crops of medusas (figs. 34 and 37)
which detach themselves and swim away to deposit their
eggs (alternation of generations). The Hydromedusa? never
produce medusae by strobilation or transverse division of a
hydriform person, although in rare cases the cicatrix left
by a detached medusa-bud has been observed to sprout
and produce a hydriform person. Neither medusiform
nor hydriform persons of the Hydromedusce series ever
have gastral filaments (unless they are represented by the
"villi" of the Siphonophora described by Huxley, Oceanic
Ilydrozoa}, whilst the medusa-forms always possess a velum
and a comparatively simple set (four, six, or eight) of radi-
ating canals in the disc, the remains of the enteric lumen.

The complete differentiation of hydriform and medusi-
form persons existing on one and the same colony having
been attained in the Hydromedusce, further changes of a
most remarkable character were brought about in some of
the descendants of these forms. The condition which we
have so far noted is perpetuated at the present day in
Bougainvillia (Eudendrium), Campanularia, and a vast
number of the so-called hydroid polyps; others have
undergone further adaptational changes. We have to
notice at least four important additional modifications
independent of one another.

(1.) The hydriform stage was suppressed altogether,
and, as in some Scyphomedueoe, so here too the diblastula
developed directly into a medusa (Trachomedusos, Narco-
meJusce, and probably some Leptomedusce like Tliaumantias
and ^Eifiiorea, and some Ant homed lisa; like Oceania and
Turritopsis).

64

HYDROZOA

(2.) The medusiform persons being early produced did not
separate themselves from the colony, but the whole colony
became free (if it ever were fixed), the medusiform persons
carrying the hydriform persons away with them. Thus the
highly differentiated swimming and floating colonies of the
Siphonophora originated.

(3.) The medusiform persons ceased to detach themselves
from the fixed hydriform persons or colonies, and developed
the ova and sperm within themselves, whilst still small in
size and attached to the hydriform stock. Having once
abandoned the detached, free-swimming life, the medusae
underwent in different genera a varying amount of degene-
ration and atrophy, of which we have in existence all

FIG. 17. Diagrams illustrating the gradual degeneration of the medusa bud
into the form of a sporosac. The black represents the enteric cavity and its con-
tinuations; the lighter shading represents the genital products (ova or sperm).
A, medusiform person still attached by 11 stalk at trie aboral pole to a colony
(plianeroeodonic gonophor of Altaian) ; B, modified medusiform person, with
margin of the disc (umbrella) united above and imperforate(mouthless) manu-
brium (adelocodonic gonuphor of Allman) ; C. sporosac, with incomplete
extension of the enteric cuvity into the umbrella, rudimentary invagination
above to form the sub-umbrella cav'ty; D, sporosac with manubrial portion
only of the enteric cavity ; E, sporosac without any trace of manubrium.

possible degrees, leading from the fixed " plianeroeodonic
gonophors " (Allman, bell-like genital buds) of many
Siphonophora through the " adelocodonic gonophors "
(genital buds with the bell no longer open but closed by the
union of the margins of the disc) of Cordylophora to the
sporosacs of Hydractinia, and even to the simple genital
warts of the little degenerate Hydra viridis of fresh waters
(see fig. 17, and explanation). By this process a large num-

Fir.. 18. Two female sporosacs (degenerate medusa?) of fft/dractiiria echinata.
(From Gegenbaur, after Van Beneden.) a, ectoderm; 6, endoderm; o, egg-
cells; (/, enteric cavity. In A an invagination of the ectoderm, which is
more complete in B, represents the rudiment of the sub-umbrella space.

ber of HydromediiscK (figs. 35, 38, 3D, 40, and 42) have lost
all evidence of the real characters of their medusa-forms, just
as others have suppressed the evidence of their hydra-forms
by direct development from the egg ; and inasmuch as both
these processes take place in genera having the closest affinity
with genera in which both hydra-form and medusa-form are
fully preserved, it is not possible to erect groups similar to
the Haplojnorpha of Gurus or the Jf'iiiopin.-<t of Allman for
their reception. The difficulty of classification is, however,
rendered very great, fora double system becomes necessary,
which shall deal with the characters of hydriform and
medusiform persons in parallel equivalent series. The
difficulty is considerably enhanced when we find that iden-
tical medusa-forms may spring from unlike hydra-forms,
and, conversely, that closely allied hydra-forms may give
rise to very different medusa-forms. The character first
noticed by Rapp as distinguishing the hydroid polyps from
the coral-polyps, namely, that of developing their geuitalia
as external bodies (Exoarii) instead of internally (Endoarii),

is seen by the considerations just adduced to be fallacious.
The Hydromedusce, it is true, often (not always) develop
their generative products from the ectoderm, and the geni-
talia frequently project as ridges and discharge themselves
directly to the exterior in this division. The Hydromedusce
contrast in this respect with the Scyphomedusce and An-
thozoa, which develop their genitalia from the endoderm,
and are (to use Rapp's terms) Endoarii whilst the former
are Exoarii. But the bodies mistaken for external generative
organs by Rapp and other early observers in many hyclroids,
and in Htjdra itself, are aborted degenerate medusae.

(4.) A further set of changes, which have affected the
original hydriform colonies and their medusa-buds so as to
produce new complications of structure among the Hydro-
medusce, are summed up under the head of " polymorphism."
The differentiation of hydriform and medusiform persons is
a case of dimorphism ; a further distribution of functions,
with corresponding modification of form, gives us "polymor-
phism." Polymorphism is unknown in the Scyphomedusce,
and it is chiefly confined to two groups of Hydromedusa? (the
Hydrocorallinae and the Siphonophora). In the hydriform
colonies of Ilt/dractinia (one of the Gymnoblasfea-Ant/tome-
dusce) the outer hydriform persons of the colony (fig. 39)
differ in form from the rest, and have wart-like tentacles. In
the same genus, and also in many Calyptoblastea, the hydri-
form persons which are destined especially to give origin
to medusa-buds are devoid of tentacles and mouth, and
are known as blastostyles (Allman), (fig. 43). In Hydro-
corallince (fig. 53) elongated hydriform persons (dacty-
lozooids) with no mouth and sporadic tentacles are set in
series around a central short mouth-bearing person (gastro-
zooids) forming the " cyclo-systems " of Mr Moseley (figs.
52 and 55). In the Siphonophora, in addition to nutritive
(hydriform) persons and generative (medusiform) persons,
there may be rows of swimming-bells (medusae devoid of
mouth and of genitalia), covering-pieces (flattened medusae),
and tentacle -bearers (hydriform persons with one long highly-
developed tentacle), (see figs. 56 and 57).

Hypothesis of the Individuation of Organs. The building
up of complex individualities, such as a hydrozoon colony,
a flowering plant, or a segmented worm or arthropod in
any one of which a number of common units are repeated,
but with varied form and function in each part of the com-
pound body is generally admitted to be explicable in two
ways, and which of the two explanations may be adopted
in any one case must depend on the ultimate inference
from a wide series of observations. The first hypothesis,
which undoubtedly applies to the ordinary hydriform
colonies of Hydrozoa, to the segments of Tcenia, and to
plants formed by the repetition of phyllomes, is that an
original unit like those which constitute the composite
organism has freely budded, and repeated its own structure
in the well-marked units which remain conjoined to form an
aborescent or linear aggregate. This is " eumerogenesis,"
and such aggregates may be termed eumeristic. By a
division of labour and consequent modification of form
among the units of a eumeristic aggregate, such an aggregate
may (in the course of phylogeny) acquire varied shape and
definite grouping of its constituent units, and a high speci-
alization as an individual. The high degree of individua-
tion which may be thus attained is due to the more or
less complete synthesis of a eumeristic colony. The more
highly individuated Chajtopods and Arthropods are syn-
thesized linear colonies. The cyclo-systems of the Hydro-
corallines are undoubted examples of synthesized colonies.
The second hypothesis is one which is applicable to cases
which, in the absence of special evidence to the contrary,
might be regarded as highly synthesized colonies. Accord-
ing to this second hypothesis, such highly individuated
composite organisms have not (in their phylogeny) passed

HYDROZOA

65

through a eumeristic phase in which the units were well
developed and alike, but the tendency to bud-formation
(whether lateral, linear, or radial) has all along acted con-
currently with a powerful synthetic tendency, so that new
units have from the first made but a gradual and disguised
appearance. This is "dysmerogenesis," and such aggregates
as exhibit it may be called dysmeristic. In dysmeristic
forms the individuality of the primary unit dominates from
the first, and the merogenesis (segmentation or bud-forma-
tion) can only show itself by partially here and more com-
pletely there compelling (as it were) the organs or regions
of the body of the primary unit to assume the form of new
units. The arms of star-fishes are, when we consider them
as derived from the antimera of a Holothurian, explained
as examples of dysmerogenesis. So, too, the series of
segments constituting a leech, and probably also the
segments of a vertebrate. Eutnerogenesis and dysmero-
genesis are only variations of one process, merogenesis, and
no sharp line can be drawn between them. Individuation
may appear at any period in the phylogeny of a eumeristic
aggregate and synthesize its units. On the other hand, in-
dividuation is more or less completely dominant throughout
the history of a dysmeristic aggregate, and is gradually
broken down as a more and more complete analysis of the
primary unit into new units is effected. It will be observed,
however, that in dysmerogeuesis, tiie/orm which individua-
tion tends to preserve is that of the primary unit (notably
the case in leeches as compared with the ameristic flukes),
whereas when we have eumerogenesis followed by synthesis
the resulting form-individuality is something absolutely
new. Thus, using the terms eumeromorph and dysmero-
morph, we have (1) synthesized eumeromorph simulates
normal dysmeromorph ; (2) aualysized dysmeromorph
simulates normal eumeromorph.

Whether the fixed hydriform colonies of the Hydrozoa,
with their more or less complete medusiform buds, and
further, the floating colonies of Siphrmophora, with their
polymorphous units, are to be regarded as synthesized
eumeroinorphs or as dysmeromorphs, more or less analysed,
is perhaps still open to discussion. The former view (that
adopted here) is that held by Allrnan (Monograph of the
Tubtdarian Hydroids, 1874), by Leuckart (1851), by
Gegenbaur (Grundriss, 1874), by Glaus (Grundziige der
Zoolof/ie, 1876), and by the Hertwigs (Organismus der
Medusen, 1878). On the other hand, Huxley (Oceanic
Hydro-Mi, 1856), formerly Gegenbaur (Zur Lehre der Gene-
rations -IVechsel, 1854), and, more recently, Ed. Van Beneden
(" De la distinction originelle du testicule et de 1'ovaire,"
Hull. Antd. Roy. Bely., 1874) have held that the medusi-
form person is a generative wart which has gradually
assumed the characters of a bud, and that the various
phases presented by it in different genera are so many more
or less successful strivings after complete assumption of the
hydra-form (from which the medusa-form is thus secondarily
derived). Similarly the variously modified units of the
siphonophorous colony have been regarded as the organs of
a parent unit which have each more or less completely
acquired the form of that parent unit, or, in other words,
the colonies in question have been held to be dysmero-
morphs. Recently ascertained facts as to the polymorphism
of HydrocoralliruB, but more especially the demonstration
of the identity of structure of the medusae of the Scypho-
medusan and Hydromedusan groups, and, further, the mode
of development of the Scypkomedusoe from the scyphistoma
and the relations of the generative products to the enteric
cavity, combine to render the view that the polymorphous
and dimorphous colonies of Hydrozoa are synthesized
eumeromorphs more probable, in the judgment of the
present writer, than that which would explain them as
dysmeromorphs.

The term "merogenesis," and its subordinate terms,
"eumerogenesis, dysmerogenesis," &c., are applicable to
units of the first order, namely, cells, as well as to the
" persons " which are built up by them. Ordinary cell-
division is an example of eumerogenesis; free-formation of
nuclei, as in the fertilized ovum of Arthropods, is dysmero-
genesis. A syncytium is usually a synthesized eumero-
morph, but may be a dysmeromorph.

Definition of the Hydrozoa. The Hydrozoa are Ccelentera
nematophom, distinguished from the fellow-group Anthozua
(the name applied to Actinozoa when the Ctenophora are
removed from them) by not possessing the latter's constant
and sharp differentiation of the arch-enteric cavity into
axial digestive and periaxial septate portions, usually by a
simpler form of nematocyst, and generally by lower histo
logical differentiation. 1

The following is a brief summary of the chief characters
of the larger divisions of the Hydrozoa:

Sub-class I. SCYPHOMEDITS^E. These are Hydrozoa which
in the adult condition al-
ways have four or eight
interradial groups of
gastral filaments ("pha-
celle"ofHaeckel)(figs. 16
(6),23,and26). Thegeni-
talia (ovaria and sper-
maria) are developed from
endoderm, and are always
iuterradial (in the four

radii formed after the first FlG . 19. Diagrammatic vertical section of a

four). The hydra-form
is not a " hydroid," but a
short polyp with broad
hypostome the "scyphi-
stoma," which gives rise to
medusa-forms by trans-
verse fission (strobilation),
or itself develops genitalia
(Lucernarice). Combined visual and auditory organs in
the form of modified tentacles (tentaculocysts) to the
number of four, eight, or more occur on the edge of the
disc (except in Lucerne/rice, where they are represented
by the "colleto-cystophors''), The medusa-form in some
cases develops from the egg without the intermediate
scyphistoma-stage (Pelagia, GJiarybdoea 1). The edge of
its disc is provided with lappets, which cover the sensorial
tentaculocysts (hence Steganophtluilmia of Forbes), and is
not provided with a velum (hence "Acraspeda" of Gegen-
baur), excepting the rudimentary velum of Amelia (fig. 31)
and the well-developed vascular velum (pseudo-velum) of
Charybdcea (fig. 21). There is no continuous marginal
nerve-ring (except in Charybdcea), but several separate
marginal nerve centres (hence Toponeura of Eimer). The

1 Quite recently the Hertwigs (Jenaische Zeitschr., bd. vi., new
series, 1879) have insisted that in the ffydromedusas the genitalia
(both ova and testes) are developed from the ectoderm, whilst in the
Scyphomedusce and in the Anthozoa they develop from the endoderm.
On this account they propose to abandon the grouping into Hydrozoa
and Anthozoa of Ccelentera ncmatophora, and suggest two groups, the
Ectocarpece and the Endocarpece the former equivalent to Hydro-
medusce, the latter embracing Scyphomedusce and Anthozoa. The
Anthozoa exhibit a further predominance of the endoderm in its ex-
tensive origination in them of muscular fibre, which but rarely and in
small quantity develops from endoderm in the Hydromedvsa: or in the
Scyphomedusce. The Hertwigs base their generalization on their own
studies of medusas, but they have ignored the observations of Van
Beneden on Hydractinia and of Ciamician on vaiious Tubularians, in
which the origin of either sperm or ova from endoderm is established.
Recently Fraipont has repeated an observation of Van Beneden's on
Cainpanitlaria, and shown conclusively that the ova in that form arise
from endoderm. Weismann (Zoologischer Aiizcii/p/', May 1SSO) shows
the same for Plumularidce and Scrtulnrida:; the reader is referred to
his paper. 1

Lucernai'ia in the plane of an intervuclius.
a, one of the inttM-radial angles of the
disc, giving rise at a' to two groups of
tentacles adradial in position; ft, axial en-
teric cavity; f, endoderm; d, band-like
genital gland (ovary or tcstis). adradial in
position, and attached to the inten-ndial
septum which runs along the angular pro-
cess of the disc, to which the letters c, d
point; p, aboral region or "foot"; z t the
interradial gastral filaments or phacelia?.
(After Allrnan.)

66

HYDROZOA

diblastula in all cases, as yet observed, is formed by in-
vagination, the blastopore closing up (Balfour).

. 23.

FIG. 20. Chanjbdiea marsvf>f<ilis (natural size, after Clans). The four annulated
tentacles are seen denending from the four lappets placed at the four corners of
the quadrangular umbrella. These are interradial. Two of the four perradial
enteric pouches of the umbrella, representing radiating canals, are seen of a pale
tint. Fg, gastral filaments (interradial); R. the modified perradial tentacles
forming tentaculocysts; (?, corner ridge facing the observer and dividing
adjacent pouches of the umbrella; OF, position of one of the genital bands.

FIG. 21. View of the margin of the umbrella of Cfiari/lxJcFti n/di-.oipi'tlis (natural
size, after Glaus). At the four comers are seen the lappets which support the
long tentacles, and in the middle of each of the four sides is seen a tentaculo-
cyst. Vet, the vascular velum or pseudo-velum, with its branched vessels.

FIG. 22. Horizontal section through the umbrella and manubrium of Cliartibdtea
marsupidUs (modified from Glaus). Ma, mnmibriuin; 8R, side ridge (perradial);
CR, corner ridges, separated by CO, the interradial corner groove; On, the
genital lamella in section, projecting from the interradial angles on each side
into UE, the enteric pouches of the umbrella; SU, the sub- umbrella space.

FIG. 23. Vertical sections of Chftriibdwa marstii'nitix, to the left in the plane of
an interradius, to the right in the plane of a pcrradius. Ma, manubrium;
EAx. axial enteron; Gh, gastral filaments (/t/iacellce); CO, corner groove;
SR, side ridge ; EnL, endndenn lamelli (line of concrescence of the walls of
the enteric cavity of the umbrella, whereby its single chamber is broken up into
four pouches) ; He, line of attachment of a genital band; EU, enteric nouch of
the umbrella, in the Irft-haiid figure, points to the cavity uniting neighbouring
pouches near the. margin of the umbrella and giving origin to TCa, the tentacular
canal; 7%, velum; Fi\ freuum of the velum ; 7V, tcntaculocyst.

The binary division of the Hydrozoa was established by Esch-
scholtz (System dcr Acfilcphcn, 1829) whose Discophorce phanero-
carjicc correspond to the Hniiilwiiu-dusir, whilst his Discophorce
cryptocarpcc represent the Hijdromcihisce. The terms point to dis-
tinctions which are not valid. In 1853 Kolliker used the term Dis-

cophora for the Scyphomedusce alone, an illegitimate limitation ol
the term which was followed by Louis Agassiz in I860. Nichol-
son has used the term in the reverse sense for a heterogeneous

abandonment necessary. The teim Discomcduscc was used for the
ScypTumedusce by Haeckel in his Generclle Morpholoijie (exclud-
ing Charybdcea) whilst Carus (Handlmch, 1867) confines the term
" Medusa: " to them alone, which is objectionable, since it belongs
as justly to the Hijdromcduscr. Forbes's term for them, Stcyanojih-
thahnia, indicates a true characteristic, failing only in the Luccr-
naricc, but its complementary term Gfymnophtkalmia is inaccurate.
Similarly tlie terms Acraspeda and its complement OmspcMa are
inaeceptable. Eimer his proposed to use the terms Tujmncura and
C'yclonctira for the two divisions but Charybd(ea appears to break
down this division as so many others. The old term Acalcphce,
which is retained by Gegenbaur in its proper sense for all the
Ccr-lcntera iicmatophom, is used as the designation of the Scypho-
medusa: alone by Claus (Grundzuge dcr ZooL, 1878), which cannot
fail to produce confusion. The term Luccrnaridec, proposed so long
ago as 1856 by Huxley (Med. Times and Gazette), most truly indi-
cates the relationships of these organisms which he was the first to
recognize, but it seems desirable to restrict this term to the limited
order in which Lucernaria is placed, and to employ for the larger
group Scyphomediisa: a term which is the true complement of
the convenient name assigned to the other division ot Hydrozoa,
viz., ITydromedusce. 1

Order 1. Lucemariae, SeyphomedustB devoid of tenta-
culocysts, with the aboral pole of the body produced into
an adhesive disc by which the organism (which possesses
the power of swimming by contraction of the circular
muscular zone of the hypostome) usually affixes itself. The
enteric cavity is divided into four perradial chambers by
four delicate interradial 2 septa. The genitalia are developed
as four-paired ridges at the sides of the interradial septa
on the oral wall of the chambers (fig. 19). No reproduc-
tion by fission nor "alternation of generations" is known
in the group. At the edges of the disc capitate tentacles
are developed in eight adradial 2 groups ; between these are
modified tentacles in some genera, the marginal anchors
or colleto-cystophors. The canal system which has sometimes
been described in them is a product of erroneous observation.
A very few genera and species of this order are known.
They may be justly called the ccenotype of the medusae
(James Clark), and their relationship to the free swimming
forms may be compared, as was done by L. Agassiz, to the
relationship of the stalked Crinoids to such forms as Coma-
tula. Three species are not uncommon on the British coasts.

By Milne Edwards the animals forming this group were termed
PodacthiariaaMd associated with the Antho~oa. By Leuckart they
were termed Calycozoa ; it is only of late that the closeness of their
relationship to the Scyphomedusce has been fully recognized, though
long since insisted on by Huxley and by James Clark. Haeckel in
his new system of the medusa; (ititzmirisbcr. dcr Jenaischc Grxcllschafl
fur Medicin und Naturwiss. , July 26, 1878) adopts for them the
term Scypkomcduscu in allusion to their permanently maintaining the
distinctive features of the scyphistoma larval form of the Acraspcdce,
the term which he adopts from Gegenbaur for our Scyphomedusas.

Order 2. Discomedusce. These are Scyphomedusce de-
veloping as sexual medusiform persons by transverse fission
from a scyphistoma, or else directly from the egg. They
have eight tentaculocysts, four perradial, four interradial,
and sometimes accessory ones (adradial). Four or eight
genital lobes (ovaria or spermaria or hermaphrodite) are
developed from the endoderm forming the oral floor of the
central region of the enteric cavity, which is produced into
a corresponding number of pouches. The mouth is either
a simple opening at the termination of a rudimentary
manubrium (sub-order Cubostomce), or it is provided with
four or eight arm-like processes (sub-orders Semostoma? and
Rhizostomce). In the sub-order Rhizostomce (fig. 24, ), the

1 Scyphomeduscr (<rKu<t>os, a cup) are medusae which are related by
strobilation to Scyphistoma, a wide-mouthed polyp with four gastral
ridges. HydffotnedustK are medusn? related to a Jlydra, a narrower
polyp, devoid of gastral ridges, by lateral gemmation,

a For use of these terms see paragraphs ou Amelia below.

HYDROZOA

edges of the oral opening fuse together at an early age
and leave several sucker-like secondary mouths, which were
formerly mistaken for independent persons. The central
enteric chamber is continued through the disc by a com-
plicated often reticulate system of radiating canals, which
excavate the endoderm lamella.

FIG. 24. ScyphomedusK. a, Rhizostoma p ulmo- b, Chrysaora hyosceita

In the Semostoma? and Rhizostomce (not in the Cubostomit)
four remarkable (respiratory) sub-genital pits (fig, 28) are
hollowed out in the gelatinous substance of the sub-umbrella
(oral face of the umbrella). These do not communicate, as

development have recently formed the subject of investiga-
tion by Claus, Eimer, and others. As the current accounts

FIG. 25. Four stages in the development of Chrysaora. A, Diblastula stage ;
B, stage after closure ol blastopore; C. fixeil larva with commencing stomodieum
or oral ingrowth ; D, fixed larva with mouth, short tentacles, Ac. ; 'ep, ectoderm ;
hy, endoderm ; st, stomodjeum ; m, mouth ; &/, blastopore. (From balfour, after
Claus.)

has been erroneously supposed, with the genital organs, the
products of which normally are evacuated by the mouth.
In the Tetragamelian Rhizostomce these pits remain distinct
from one another as in Semostomce, but in the Monogamelian
Rhizostomce they unite to form one continuous sub-genital
cavity placed between the wall of the enteric cavity and
the polystomous oral disc. The common English forms,
Aurelia, Chrysaora, and Cyancea, are types of the Seino-
stonue, the somewhat less common Rhizostoma of the
Monogamelian Rhizostomw, whilst Nausithoe and Disco-
medusa represent the simple C'ubostomce.

The writer has adopted the term used by Haeckel for this order,
and is indebted to his preliminary notices of a large work on the
Medusa:, now in the press, for outlines of the classification and de-
finitions which have been introduced with modifications in relation
to these and the other Medusa:. The term Discophora is used by
Glaus (Gnuulzilije) for the Discomcduscc. It is quite clear from the
varied and inconsistent use by different authors of that term, and
also of the terms Acalephce and Medusa, that they must be ejected
altogether from use in systematic treatises.

The structure of the common Aurelia aurita and its

FIG. 21!. Later development, of Chrysaora and Aurelia (after Claus). A, Scyphi-
stoma of Cltrysaora, with four perradial tentacles and horny basal perisarc.
B, Oral surface of later stage of scyphistoma of Am elia, with commencement
of four intervadial tentacles. The quadrangular mouth is seen in the centre ;
the outline of the stomach wall, seen by transparency around it, is nipped in
four places interradially to form the four gastric ridges. C, Oral surface of
a sixteen-tentacled scyphistoma of Aurelia. The four gastric interradial
ridges are seen through the mouth. I>, First constriction of the Aurelia
[ scyphistoma to form the pile of ephyrje or young medusie (see fig 27). The
single ephyra carries the sixteen scyphistoma tentacles, which will atrophy
and disappear The four longitudinal gastric ridges are seen by tiansparency.
E, Young epliyra just liberated, showing the eight bifurcate arms of the disc
and the internidial single gastral filaments. F, Ephyra developing into a
medusa by the growth of the adradial regions. The gastrul filaments have
Increased to three in each of the four sets. ^4, margin of the mouth; Ad,
adradial radius; F, gastral filament; //;, interradial radius; JG, adradrial
gastral canal ; Jfi=R 3 , adradial lobe of the disc ; K, lappet of a perradial arm ;
M, stomach wall; Afst, muscle of the gastral ridge; J/(P. gastral ridge;
J/s, mesoderm ; 0, tentaculocyst ; P, perradial radius ; A'-, interradial radius ;
R*, adradial radius; SO, commencement of lateral vessel.

in text-books are very inadequate, a short sketch of the

morphology of that form is appended here.
From the egg, according

to the researches of Claus

(whose figures, here repro-

duced, refer more especially \ /

to the closely allied genus \ /

Chrysaora, up to the compl e- \L
tion of the scyphistoma), a
single-cell-layered blastula de-
velops which forms a diblastula
by invagination (fig. 25, A, B,
C). The orifice of invagination
closes up, and the ciliated
" planula " (as this stage used
to be termed in all Ceelentera),
after swimming around for a
time, fixes itself, probably by FlG 27 ._ DcveIopment of Aurelia .
the blastoporal pole. The true Above to left, young scyphistoma
mouth then forms by inruption
at the opposite pole. Two ten-
tacles now grow out near the
mouth opposite to one another
(fig. 25, D), and are followed
by two more (fig. 26), these
indicating the four primary
radii of the body which pass
through the angles of the four-
sided mouth, and are termed perradial. Meanwhile
the aboral pole narrows and forms a distinct stalk,
which in Chrysaora secretes a horny perisarc (fig. 25,

with four pel radial tentacles Be-
low to left, scyphistoma with six-
teen tentacles and first constiiction.
To the light, stiobila condition of
the scyphistoma, consisting of thir-
teen metameric segments ; the up-
permost Still pn-^^-l-s Illr Mxtrcn

tentacles of the scyphi>toma; the
remainder have no tentacles, but
are ephyrje, each with eight bifid
arms (processes of the disc). Each
segment when detached becomes
an ephyra, such as that drawn in
tig. 26, E, F. (From Gegenbaur )

68

HYDROZOA

D). Four new tentacles, those of the intermediate or
secondary radii, now appeaf between the first four, and
are termed interradial. At the same time four longi-
tudinal ridges grow forward on the wall of the enteric
cavity (fig. 26). These interradial ridges have sometimes

Tc

FIG. 28. Surface view of the sub-umbrella or oral aspect of Aurelia aurita, to
show the position of the openings of the sub-genital pits, GP. In the centre
is the mouth, with four pel-radial arms corresponding to its angles (compare
fig. 26). The four sub-genital pits are seen to be interracial, x indicates tlie
outline of the roof (uboral limit) of a sub-genital pit; y, the outline of its floor
or oral limit, in which is the opening (compare 6 of fig. 16).

been erroneously described as containing each a longitudinal
canal connected with a circular canal at the base of the
tentacles. They are in reality solid, as is the margin of the
hypostome from which the tentacles spring. It is in con-
nexion with these four
ridges that the gastral
filaments will subse-
quently appear, as also
the genital organs either
along their middle line
or adradially to them.
The ridges correspond
tu the mesenteries of
the Authozoa. Eight
additional tentacles
placed one on each side
of the perradial ten-
tacles (or of the inter-
radial, according as we
may choose to regard
the matter) next appear,
and are distinguished as
iiiln.iifial. All the ten-
tacles reaching an equal
size, we obtain the ap-
pearance seen in fig. 26,

when the vouno- scvnhi F '- 2!l - Half of ' e lower surface of Aurelia
1L / Ul ' ,iurila. Tlu- transparent tissues allow the

stoma is looked at from
above. Looked at from
the side, with its wide
hypostome and short

vertical axis, the scy- are not d ""- (from G<.- g enbaur.)
phistoma differs widely from an ordinary hydra-form, and
approaches the medusa-form, to which its fnur longitudinal
gastral ridges further assimilate it. The little creature is
now about an eighth of an inch in height ; in other genera,
but not in Chrysaora, it may now multiply by the produc-
tion of a few buds frum its fixed basal disc. After nourish-
ing itself for a period, and increasing to four or five times
the size just noted, the vertical axis elongates and a series
of transverse constrictions appear on the surface, marking
off the body of the scyphistoma into a series of discs
(figs. 26 and 27), each of which by the development

ispan

enteric cavities and canals to be seen through
tin-Mi. '/, marginal lappets hiding tentaculo-
cysts; b, oral arms; r, axial or gastric portion
of the enteric cavity; gr, radiating and ana-
stomosing canals of the enteric system; ov,
ovaries. The gastral filaments near to these
are not drawn.

of tentacles and completion of the constriction will become
a separate medusa (in its young state called " ephyra ").
The tentacles of the Aurelia and the structure of the
margin of its hypostome are very different from those of
the scyphistoma. They are exhibited in their earliest
condition (when the vl?Wia-medusa is first liberated from
its attachment and is an ephyra) in fig. 26, E, F. The
margin of the hypostome is drawn out into eight arms
(which are not to be confused with tentacles) ; the end of
each arm is bifid, carrying a pair of lappets the marginal
lappets which persist in the adult (see figs. 30 and 31). Be-
tween the lappets is placed a short and peculiar tentacle, the
tentaculocyst or sense-organ. The eight arms of the disc
and their tentaculocysts are perradial and interradial. As
the organism grows, a set of eight arlradial tentacles appear
in the notches between the eight arms, but never attain any
relatively large size in Aurelia. The asteroid arm-bearing

End

FIG. 30. Tentaculocyst and marginal lappets of Amelia aurita. In the left-
hand figure ML, marginal lappets; T, tentaculocyst; ^4, superior or aboral
olfactory pit ; MT, marginal tentacles of the disc. The view is from the aboral
surface, magnified about r>0 diameters. In the right-hand figure A, superior
or aboral olfactnry pit; 11, inferior or adoral olfactory pit ; //, bridge between
the two marginal lappets forming the hood ; T, tentaculucyst ; En<l. cndoderm ;
Ent, canal of the enteric system continued into the tentaculocyst; Can, endo-
dermal concretion (auditory); oc, ectodermal pigment (ocellus). The drawim;
represents a section, taken in a radial veitical plane so as to pass through the
long axis of the tentaculocyst. (After Eimer.)

character of the margin of the disc is soon obliterated by

the relative growth of the intermediate adradial areas, which

become quite filled up, so that in the adult the tentaculocyst

is carried in a notch instead of on a prominence, and is

concealed by the two lappets

(figs. 28 and 30). The margin

of the disc between adjacent

pairs of lappets gives rise to

a fold which grows inwards

(toward the mouth) during

an early stage (fig. 31), and

numerous small tentacles (the

fringe) appear along the

margin of the disc, which

soon equal in size the first

adradial tentacle. The in-

, . . . , , FIG. 31. Part of the margin of the disc

growing told IS the velum or of a young Aunlia. to show therudi-

" nspndo velum " incl never enta>y velum, r,/, extending from
pseuao-veium, dim never the ma ,. gi , Uil laI , pL . tSi 1!L< eitllcl .

increases in size, SO that in

the adult it is not observ-
able. The tentacles also remain very small and fine in
Aurelia, forming a continuous fringe along the edge of
the disc, interrupted only by the eight notches for the
tentaculocysts (fig. 29).

The sixteen tentacles of the scyphistoma are necessarily
attached to the most anterior of the pile of medusa; ; they
atrophy, but to what extent they may be metamorphosed
to form the parts of the ephyra or young medusa has not
been determined. The scyphistoma, having given rise to
its pile of ephyr, may (in some genera, Awelial)
redevelop its own kind of tentacles below the constriction
marking off the last ephyra. Hence scyphistoma tentacles
appear sometimes at the top and sometimes at the bottom

side; T', the small tentacles fringing

HYDROZOA

69

of the pile, which has led to diverse accounts of the mode
of development of the ephyrre.

Whilst changes are going on in the configuration of the
margin of the disc of an ephyra on its way to the perfect
form of the adult Aurelia, the enteric cavity has also under-
gone most important changes. Foremost in importance is
the development of a single gastral filament on each of the
four gastral ridges which necessarily are present in the
transverse slice (so to call it) of a scyphistoma, which
becomes an ephyra (fig. 26). These rapidly increase in
number as the ephyra grows. Further, the enteric cavity
at first follows the outline of the ephyra, sending a process
into each arm, but then by adhesion of its walls is converted
into a four-lobed central chamber, a marginal canal, and an
endoderm lamella. A system of canals, the arrangement of
which is seen in figs. 29 and 31, subsequently opens out again
certain lines and tracts of the conjoined endoderm walls.

In the adult Aurelia we find the mouth surrounded by
four large arm-like perradial processes (figs. 25 and 29)
(not tentacles), and leading through a short manubrium
into a flattened four-lobed chamber, the lobes being inter-
radial, and having on their oral floor numerous gastral
filaments (rich in thread cells) (6 in fig. 16). Each pouch
or lobe gives off a canal, which runs towards the circular
canal at the margin of the disc, but breaks up into three or
four secondary canals on its way. Between the pouches
come off eight other " radiating " canals (adradial), which
do not branch, but go straight to the circular canal.

The oral lloor of the concavity of each lobe of the enteric
cavity is occupied by a horse-shoe-shaped frill (fig. 29, ov),
either testis or ovary (the sexes being in separate indi-
viduals). The open arms of the horse-shoe are turned
towards the centre of the disc, and the folds of the genital
frill are so deep as to show themselves on the outer ecto-
derrnal wall of the disc. Here, however, there is a very
remarkable arrangement, which has rarely, if ever, been
correctly described and figured in our common Aurelia.
The gelatinous substance of the disc is hollowed out on
that part of the oral face corresponding to the position of
the genital frills, so as to form four separate extensive pits
or chambers. Each of these sub-genital pits has in Aurelia
a small round opening on the oral face of the disc (fig. 28,
GP), but is otherwise entirely closed, having no com-
munication with the genital tissues, from which it is
separated by a delicate layer of ectoderm (6 in fig. 16).
The pits probably serve to admit water for respiratory pur-
poses into close proximity with the genital tissues.

The whole enteric surface, including canals, is ciliated,
whilst the ectoderm is not ciliated, but provided with
groups of nematocysts.

The tentaculocyst in the adult Aurelia is relatively an
extremely minute body, completely hidden by the two large
marginal lappets (fig. 30, T). Above it (that is, on the
aboral surface, as the Aurelia swims) is a deep pit (A),
Schafer's fovea nervosa superior, sunk in a sort of bridge
which connects the two lappets and overhangs the tenta-
culocyst. A similar pit (the fovea inferior) exists on the
oral surface. These have been recognized by Clans, Einier,
and the Hertwigs as olfactory organs. The tentaculocyst
is seen in section in fig. 30 (right-hand figure), which ex-
hibits its central cavity continuous with the enteric cavity,
its ectodermal pigment spot (eye), and its endodermal mass
of concretions (auditory organ).

The chief muscular mass of Aurelia, except that of the
oral arms, is a circular zone on the oral face of the disc.
The muscular fibres are not distinct cells, but transversely-
striated processes of the epidermic cells (epidermo-muscular
cells) (fig. 9). In the " arms " of other medusae, and pre-
sumably of Aurelia, the muscular fibre is formed by inde-
pendent nucleated cells (fig. 9).

The nerve-epithelium from the olfactory pits of Aurelia is
drawn in lig. 1 4. Starting from this and from the cells of
the teutaculocysts are nerve-fibres, which spread themselves
on the surface of the circular muscular zone in the neigh-
bourhood of the tentaculocysts, and these are connected each
and separately with large isolated nerve-ganglion cells (fig.
15). The nerve-fibre is continued beyond the cell, and
in some instances has been traced into a broadened ex-
pansion lying on a muscular fibre (Schiifer). The nerve-
ganglion cells lie very superficially immediately below the
Hat epithelium of the body surface and between it and its
muscular processes.

The ova and spermatozoa of Aurelia develop in the
genital frills from endoderm cells in separate individuals.
They pass to the exterior through the mouth.

Order 3. Conomedusce, Scyphomedusce with only four
tentaculocysts, and these perradial. A broad velum (so-
called pseudo-velum) of complete circular form is present,
differing from that of the HyJromeJnst.i' in the fact that it
is penetrated by canals of the enteric system (Charybdcea).
The whole umbrella is bell-shaped. The genital organs are
four pairs of lamellifonn ridges (fig. 22) which are attached
to the four narrow interradial septa that divide the large
enteric cavity of the umbrella into four perradial gastro-
canal pouches. The lanielliform genital glands hang freely
in these pouches. At the edge of the umbrella are four
interradial lappet-like prolongations of the gelatinous sub-
stance of the disc, which support each a long tentacle (fig.
20). The nerve-ring is complete, like that of the Hijdro-
meduscv.

There is now no doubt that Charybdcea, which has been placed in
each of the two large divisions of the Hydrozoa, must be classed
with the Scyphomedusce. The recent investigations of Glaus
(Arbcitcn aim <A m Zool. Jnstititt :.u Il'icn, Bd. i. Hf't. ii., 1878), as
well as those of Haeckel and Fritz Miiller, lead to this conclusion.
The term Conomcdusic is adopted from Haeckel, who places here,
besides Charybdim and Tamoya, other forms, a fuller description of
which may be expected in his forthcoming System tier Meduscn. In
many respects its quadrangular form, its marginal lappets, its
broad enteric pouches in place of fine canals, its vascular velum, and
its highly complicated tentaculocysts (fig. 13, tyCltni-yMaa
is peculiar. The simplicity of the enteric system and the arrange-
ment of the genital glands bring it near to Luccrnaria. The ex-
istence of four interradial groups of gastral filaments, and the dis-
position of the paired genital glands at the sides of the interradial
septa, determine its position to be among the Scyphomedusce. Its
development is not known. Figs. 20 to 23 illustrate the structure
of ChntrybdaBd,

Order 4. Peromedusae, Seyphomedusce with four inter-
radial tentaculocysts. The enteric system consists of three
divisions, an aboral main stomach with four interradial
gastral ridges and filament groups; a mid-stomach, which
communicates by means of four perradial slits with a very
large ring-sinus (occupying two-thirds of the umbrella) ; and
thirdly, an oral portion or pharynx, with four wide per-
radial pouches. The genital organs are four pairs of
sausage-shaped interradial ridges lying on the oral floor of
the ring-sinus.

This is a new group founded by Haeckel, of which we have at
present no further details.

Sub-class II. HYDROMEDUS.E. These are Hydrozoa devoid
of gastral filaments ; the sexual persons are always medusi-
form, the genital glands are developed sometimes from ecto-
dermal cells, sometimes from endoderm, and are always per-
radial (in the radii of the first order). The medusiform per-
sons always possess a muscular non-vascular velum (hence
Craspedota) and a complete nerve-ring (hence Cycloneura of
Eimer). The marginal sense-organs are either ocelli or oto-
cysts or tentaculocysts. The diblastula, in all cases as yet
observed, is formed by delamination (Balfour). The sexual
medusiform persons may develop directly from the egg, but
more usually the etrg gives rise to a hydriform person the
hydroid which difl'ers from a scyphistoma in its elongate

70

HYDROZOA

vertical axis, the indefinite number (often also position) of
its tentacles, and its frequent formation of a colony of large
size by lateral budding. By lateral budding (not by

?IG. 32. Diagram showing possible modifications of persons of a gymnoblastic
ffydromedusa. a, hydrocaulus (stem); 6, hydrorhiza (root); c, enteric cavity;
d, endoderm; c, ectoderm; f, perisarc (horny case); (/, hydranrh (hydriform
person) expanded; g', hydra'nth (hydriform person) contracted; h, hypostome,
bearing mouth at its extremity; A-, sacciform gonophor (sporosac) springing
from the hydrocaulus; k', sporosac springing from m, a modified hydriform
person (blas'tostyle): the genitalia are seen surrounding the spadix or manu-
brium; /, medusiform person or medusa; m, blastostyle. (Alter Allman.)

metameric fission) medusiform persons which alone develop
sexual glands are produced on the hydriform colonies;

FIG. 33. Diagram showing possible modifications of the persons of a Calypto-
blastic HydromeduRa. Letters a to A same as in fig. 32. I, the horny cup or
hydrothe.ca of the hydriform persons; /. medusiform person springing from in,
a modified hydriform person (blastostyle); 71, the horny case or gonangittm
enclosing the blastostyle and its buds. This and the hydrotheca t give origin
to the name Calyptoblastea. (After Allnian.)

these may separate from the colony, or may be retained in
a more or less degenerate form adherent to it, as generative
bucls or warts.

The medusiform persons of this group are the DismphariK crypto-
carpcc of Eschscholtz, the Craspcdota of Gegenbaur (1854), and the
Hydromedusida of Kolliker (1853) the last two authors at that
time separating the hydriform persons as Hydroidca. Louis
Agassiz (1860) includes both sets of persons under the term

Fig. 34.

Fig. 35.

PIG. 34. Diagram of Corymorpha. A, a hydriform person giving rise to
medusiform persons by budding from the margin of the disc; B, free swim-
ming medusa (Steenstrupia of Forbes) detached from the same, with manu-
brial genitalia (Anthomedustp) and only one tentacle. (After Allmun.)

FIG. 35. Diagram of Tubutaria irtilivisa. A single hydriform person a bearing a
stalk carrying numerous degenerate medusiform persons or sporosacs 6. (After
Allnian.)

Hijdroida (together with Lucernaria), which also is the term adopted
byAllnian in his beautiful monograph) 1871-74). J.V. Cams, amend-
ing the limitations given by Carl Vogt, was the first to use the term
Hydromcdusce in the sense here adopted (Handbuch der Zoologie,
1863), and it is now employed in the same sense by Gegenbaur
(Elements of Comparative Anatomy, London, 1878), namely, to em-
brace both the cryptocarpous medusae of Eschscholtz and the

FIG. 36. Colony of Bougainvillea fivtieosa, natural size, attached to the
underside of a piece of floating timber. (After Allman.)

hydroids related to them. The term Hydromcdusos is used unwisely
by Claus (Gnindziigc d. Z.) for the whole group of Hydrozoa. _ It
has been the practice of some authors to give a double classification
of the group one based on the characters of the medusiform per-
sons, the other on that of the hydriform persons. In the present
article a double name will in some cases be assigned to a group-
but the attempt is made to bring both sets of persons under one
system.

Order 1. GymnoUastea-Anthomedusof. These are Hydro-
medusa?, which all, as far as is known, pass through a
hydriform phase, but in which the medusiform persons
may either reach full development or exhibit the extremest
degeneration (Hydra). The ectoderm of the hydriform

HYDROZOA

71

persons may secrete a horny tubular protective case
(perisarc), hut this does not form cups for the reception of
the tentacular crown nor cases enclosing groups of medusi-
form buds (gonangia). The fully-developed medusiform

FIG. 37. Portion of colony of BougainriUea (Eiidendrhtu>)frtttico!;a (Anttiomeduscp-
catyptoblaslea) more magnified. (From Lubbnck, alter Aliman.)

persons never possess otocysts nor tentaculocysts, but always
ocelli at the base of the tentacles. The latter are usually
four or six, corresponding to the same number of simple
radial enteric canals, but may be more numerous or reduced
to one or to two ; rarely they are branched (Cladonema).

This is a very well defined group, since tlie GymnoWastea of
Allman, liased on the eh.-iraetcrs of the liydrifnrm ]iursous also
known as Tiiliiilm-in- ;\m\ iti/mnotoka correspond exactly with the
Antliniiii'iliimr of Ilaeekid'.s new system, llijdra is included here,
though placed in a separate order liy Aliman. Some of the leading
forms of hydriform and inedusiform persons are given in the cuts
(figs. 34 to 42). The greatest range in the amount of degenera-
tion of the medusiform persons is seen even in genera of the same
family e.g. , Turris and Clava the former producing free
medusse, the latter sessile .sporosacs. The (Jccanitlcc of Gegenliaur
(excluding the Williadit, which Haeekel assigns to the next group)
correspond on the whole to the medusa-forms of this order.

Fig. 41.

Fig. 42.

FIG. 41. Hydriform person of Simcorime, witlimedusifnmi persons budding from
it. and shoun in various stages of development, a, 6, c, d, e. (From Gegenbaur,
after Desor.)

FIG. 42. Hiidra riridis. ot, ovary; te, testis.

Order 2. Calyptoblastea-Leptomedmce. These are Hydro-
of which the hydriform phase is known in a
large number of cases, whilst of others only the medusa-
forms are known ; none are known to develop directly from
the egg to the medusa-form. As in the preceding group,
the medusiform persons may reach full development or

Fig. 38.

Fig. 39.

Fig. 40.

FIG. 3S. Diagram of Clara, showing a hydriform person surrounded by a
verticil of degenerate medusiform persons (sporosacs). (After Aliman.)

FIG. 39. Diagram of a colony of JJijdraclinia, showing four forms of persons, a,
hydriform person ; 6, modified hydriform person,' or blastnstyle bearing r
degi-nerate medusiform persons or sporosacs; d, mndifled hydriform person
situated at the margin of the colony (rtactylozooid). (After Aliman )

FIG. 40. Diagram of a colony of Diconjne, showing three forms of persons a,
normal hydriform person ; 6, modified bud-bearing hydriform person (blasto-
stylc); c, degenerate medusiform persons (sporosacs).' (After Aliman.)

The sexual glands are placed in the wall of the manubrium,
either equally distributed all round it or in four separate
perradial groups, which are often divided into eight ad-
radial groups by the perradial longitudinal muscles.

Fig. 43. Fig. 44.

FIG. 43. Diagram of a colony of f'ampiinularia. showing four forms of per-
sons. A, portion of a fixed colony ; a. hydrifonn person ; fc, bud-bearing
hydrifoi-m person (blastostyle) ; B, flee -swimming colony, being a sexless
medusiform person (blastocheme of Aliman), with modified medusiform persons
budding from its radiating canals, as sporosacs. (After Allmim.)

FIG. 44. Medusiform person (Li::ia), one of the Antliomeditsts, detached from a
hydroid colony of the fnmily iWi'WnW.r. ( icelli are seen at the base of the
tentacles, and two medusiform buds on the