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EDITED BY

K. RAY LANKESTER

M.A., LL.D., F.R.S.

HONORARY FELLOW OF EXETER COLLEGE, OXFORD; CORRESPONDENT OF THE INSTITUTE
OF FRANCE ; DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS
OF THE BRITISH MUSEUM

Part II
THE PORIFERA AND COKLENTERA _

o> a
oa \yr >
EK. A: MINCHIN, M.A.
PROFESSOR OF ZOOLOGY IN UNIVERSITY COLLEGE, LONDON
G. HERBERT FOWLER, BAS PRD,
LATE ASSISTANT PROFESSOR OF ZOOLOGY IN UNIVERSITY COLLEGE, LONDON
AND
GILBERT C. BOURNE, M.A.

FELLOW AND TUTOR oF NEW COLLEGE, OXFORD

WITH AN INTRODUCTION BY
E. RAY LANKESTER

LONDON
ADAM & CHARLES BLACK
1900

weg” Orr

(|
; 4 a

PREFACE

THE present volume is the “Second Part” in order of a com-
prehensive treatise on Zoology, which has been for some time
in preparation under my editorship. In this treatise each
of the larger groups of the Animal Kingdom is to be described
by a separate author; whilst, as far as possible, uniformity
in method and scope of treatment is aimed at. The authors
are, for the most part, graduates of the University of Oxford,
though it may not be possible to maintain this limitation in
future sections of the work.

The general aim of the treatise is to give a systematic
exposition of the characters of the classes and orders of the
Animal Kingdom, with a citation in due place of the families
and chief genera included in the groups discussed. The work
is addressed to the serious student of Zoology. To a large
extent the illustrations are original. A main purpose of the
Editor has been that the work shall be an independent and
trustworthy presentation, by means of the systematic survey,
or taxonomic method, of the main facts and conclusions of
Zoology, or, to speak more precisely, of Animal Morphography.

The treatise will be completed in ten parts of the size
of the present one. It will at once be apparent that this
limitation necessitates brevity in treatment which, however,
will not, it is believed, be found inconsistent with the fulfil-
ment of the scope proposed or with the utility of the work

——

WG Wwaiiieas

Ee ge
oo comian ing ~
ysl Wlution \

\
i)
}

di

vi PREFACE

to students. The immediate publication of the following
parts may be expected :—

Part I. Introduction and the Protozoa.

Part II. Enterocceela and the Ccelomoccela—The Pori-
fera— The Hydromedusae— The Scypho-
medusae—The Anthozoa—The Ctenophora

(the present volume).
Part III. The Echinoderma (published in March 1900).
Part IV. The Mesozoa—The Platyhelmia—The Nemer-

tini.

These parts will be issued, without reference to logical
sequence, as soon as they are ready for the press. This pro-
cedure to some extent evades the injustice of making an
author, whose work is finished, wait for publication until other
more tardy writers have completed their tasks.

The following authors have undertaken portions of the
work :—Professor Poulton, F.R.S., M.A.Oxon.; Professor
Weldon, F.R.S., M.A.Oxon.; Professor Benham, D.Sc., M.A.
Oxon.; Mr. G. C. Bourne, M.A.Oxon.; Mr. G. H. Fowler,
M.A.Oxon.; Professor Minchin, M.A.Oxon.; Mr. F. A. Bather,
M.A.Oxon.; Professor J. W. Gregory, D.Sc.; and Mr. E. 8.

Goodrich, M.A.Oxon.
FE. RAY LANKESTER.

August 1900.

ube cilia

CONTENTS

CHAPTER II.—THE ENTEROCEHLA AND THE C@LOMOCELA.
CHAPTER IIJ.—SpoNGES—PHYLUM PORIFERA.

CHAPTER IV.—THE HYDROMEDUSAE.

CHAPTER V.—THE SCYPHOMEDUSAE.

CHAPTER VI.—THE ANTHOZOA.

CHAPTER VIJ.—THE CTENOPHORA.

CHAPTER II
THE ENTEROCELA AND THE CQ@ELOMOCELA !

1. THE DISTINCTION BETWEEN THE GRADES PROTOZOA AND
MeETAZOA.—Some discussion of this subject will be found in the first
part of the present work. Here we start with the simplest con-
ception of a Metazoon, namely, a multicellular organism (7.e. an
organism which can be iseapi | M as well as optically resolved into
a number of constituent “cells” or “ cytes”) in which the cell-units
are differentiated into at least = groups, having contrasted pro-
perties and functions instead of being equiformal ‘and inter change-
able in function as in the multicellular Protozoa. The production
of micro- and macro-gametes or male and female reproductive con-
jugating cells does not in itself serve to distinguish the Metazoa
from the Protozoa, as this occurs not only in multicellular, but
also in unicellular Protozoa (Coccidia, Hemamcebe). The group-
ing of at least two different kinds of cell-units to form at least
two distinct permanent layers or masses in the adult organism
is the essential character of the Metazoa, and it does not constitute
a very great chasm between them and some of the aggregated or
multicellular Protozoa.

2. DIVISION OF THE METAzOA INTO Two BraNncHEs.—The
Metazoa ” are divisible into two divergent branches, which possibly
may be really two independent stems arising separately from
widely different ancestral Protozoa. These are, on the one hand, the
Parazoa * or Sponges, and, on the other hand, the Enterozoa,* which
comprise the rest of the animal kingdom. The Parazoa are charac-
terised by being composed of aggregates of cells, of which the outer
layer is protective, trophic, and reproductive in function, whilst the

1 By E. Ray Lankester, M.A., F.R.S.

° The term Metazoa was introduced by Haeckel in his Studien zur Gastrea
Theorie, Jena, 1877, p.12 and p. 54. Protozoa is a translation of the German word
“Urthiere,” and was first used by von Siebold in 1841.

3 This term is due to Sollas ; see Quart. Journ. Microsc. Sci. N.S. vol. xxiv. p.
614 (1884).

4 The name Enterozoa was introduced by me in 1876 (preface to the English
translation of Gegenbaur’s Comparative Anatomy) as a substitute for Haeckel’s term

Metazoa. It now finds convenient application as the title for one of the two branches
into which Metazoa are divisible.

I

2 PARAZOA AND ENTEROZOA

innermost has its units in the shape of goblets from the interior
of which rises a vibratile flagellum (choanocytes). They bound
a cavity excavated in the mass of cells, and communicating by
apertures, with the exterior. By the movements of their flagella
they induce the flow of currents of water within the cavity or
chamber which they line! The Enterozoa, on the other hand, are
in their simplest expression, two-cell-layered sacs, the outer layer
of cells—the ectoderm—being protective, respiratory, and excre-
tory, and often provided with vibratile processes, whilst the inner
or endoderm cells are essentially concerned in digestion, assimila-
tion, and reproduction and bound a cavity. This cavity is the
primitive gut or “archenteron,” and opens to the exterior by a
single aperture, the mouth-anus.

The most primitive Enterozoa retain the general features thus
indicated, whilst it is possible to trace the development of the in-
dividual in the case of representatives of the higher groups of
Enterozoa from the same simple structure (the embryonic form
known as the Diblastula or Gastrula).

PARAZOA ENTEROZOA

»

\ S

Branch AN ees B

y,
Vv

Grade B. METAZOA.
A

Grade A. PROTOZOA.

TREE showing primary grades and branches of the Animal Pedigree.

3. STERILITY OF THE BRANCH PARAzoA.—The Parazoa have
apparently not given rise to any very great advance or complication of
structure. They are represented by the Sponges or Porifera alone.

4. THe DivisioN OF THE BRANCH ENTEROZOA INTO Two
GrabDES.—The Enterozoa proceeding from the condition of simple
two-cell-layered sacs (Fig. 1) have given rise to an immensely
increased complexity of structure, and to a vast diversity of form
and internal organisation. The most important step in their pro-
gressive development of complexity of structure is the production
of a second internal cavity distinct from the gut or archenteron
(Figs. 2 and 3). To this second cavity the name “ccelom” is
given. Its nature and origin are discussed below.

The presence of the ccelom is of the highest physiological import-
ance. Once developed it became the starting-point for a variety

1 See further the conclusion of the chapter Porifera, by Prof. Minchin,

C@ELOMIC SACS 3

Fic. 1.—SrcTions THROUGH ONE OF THE
ENTEROCELA (a Scyphistoma polyp)
TO SHOW THE SACCULATION AND Con-
TINUITY OF THE ARCHENTERON AND
THE TWO PRIMARY CELL-LAYERS.

ec, ectoderm, and en, endoderm, indi-
_ cated by dark and pale shading re-
spectively. A, sagittal section of the
diblastula embryo without oral aperture ; Ci
B, similar section of the young polyp
after fixation but without oral aperture.
s, oral in-sinking (stomodseum); g, meso-
glea. C, young polyp with mouth. sp,
junction of stomodzeum and archenteron ;
m, gastric pouch. D, transverse section
taken so as to cut the gastric pouches
(m) above their openings into the archen-
teron; s, stomodzeum. E, a similar
section at a later period when four
pouches have been formed, st, septa.
F, transverse section at a lower level,
showing the continuity of the gastric
pouches with the axial portion of the
archenteron ; ¢, teniole. (After Goette,
from Korschelt and Heider.)

q Fic. 2.—Secrions THRouGH THE Larva; oF aN EcuHrInoperM (Asterina gibbosa) at Suc-
CESSIVE STAGES OF GRowTH; A, B, C, TO sHOW THE ORIGIN OF THE CaiLom AS A PAIR
or ENTEROCG@LOUS PouUCcHEs.

‘ Zi, Blastopore; D, archenteron; Vp, vasoperitoneal sacs or ccelomic pouches. r and J,
= and left sides. (After Ludwig, from Korschelt and Heider.)

4 C@LOMIC SACS

of important differentiations and consequent development of new

organs, such as genital ducts and renal excretory glands, besides

affecting the mechanical conditions of the body-wall and muscles,

and the diffusion of chemical products within the body.

Fic. 8.—-TRANSVERSE SECTIONS OF
Two SraGEs OF THE LARVA OF
THE BRACHIOPOD ARGIOPE TO
SHOW THE ORIGIN OF THE Ca@&LOM
AS A PatR OF ENTEROCHLOUS
PouCcHEs.

A, younger stage. 0/1, blastopore ;
pv, right eceelomie pouch continuous
with me, the archenteron. JB, later
stage, the ccelomic pouch (pv) is now
shut off from the archenteron, me;
b, temporary bristles. (After Kowa-
lewsky, from Balfour.)

Accordingly we divide the Enterozoa into those in which the
sole cavity is the enteron—the Enteroccela—and those in which

the ccelom is present as an independent second cavity—the Cceelo-

moccela.!
Grade B. COLLOMOCGELA,

Grade A. ENTEROCGLA.

ENTEROZOA.

1 The two grades which I here call Enteroccela and Ceelomoccela are
often designated Ceelentera and Ceelomata. The word Cclenterata (due
to Leuckart, 1848) has been used by some authors, It seems to me that
it is legitimate to transpose the components of Ccelentera so as to form
the word Enteroceela, and we then are able to form a very much better
pair to it than is Cclomata (Haeckel’s term), by coining the word
Ccelomoceela. The contrast of animals whose sole cavity is the enteron
or gut-chamber with those which have a ccelom as an essential and dis-
tinct cavity is thus clearly expressed.

The use of the term enterocc:] for the ccelom itself, and of the word
Enterocelia for a large division of celomoccelous animals by the
Hertwigs may seem to render the conversion of Coelentera into Entero-
ccela inconvenient. But the word “enterocceelous” or “enteroccelic ” is
still quite appropriate as a description of the early phase of development
of the ewlom for the very same reason which justifies us in calling
polyps and medusz, Enteroccela or Ccelentera, viz. that we refer to the
existence of a cavity which is in origin in the one case, and permanently
in the other—a part of the enteron. As to the Hertwigs term “ Entero-

|

PHYLA OF THE ANIMAL PEDIGREE 5

5, ENUMERATION OF THE PHYLA INCLUDED IN THE GRADES
ENTEROCELA AND CaLoMOceLA.—The term “phylum” was
‘introduced by Haeckel to indicate the branches of the animal
pedigree of largest size. Setting aside the bifurcation of the
~Metazoon stem into Parazoa and Enterozoa, we use the term for
primary branches. The branches into which a phylum divides
are called, in accordance with the practice of all systematists since
Linneus introduced the system, “ classes”; those into which a class
divides “orders”; those into which an order divides are called
families, which are divisible into genera, and these again into
species. Breaks may be indicated in any of these groups by the
recognition of two or more “ grades” within it, whilst divergences
of importance giving rise to two or more lines of descent can be
further pointed out by the additional groupings furnished by the
_ prefix “sub,” such as sub-phylum, sub-class, sub-order, ete.

We recognise the following phyla in the two grades of
Enterozoa :—

GRADE A. Enterocela.

HYDROMEDUS&.

Phyla~ ScypHOoMEDUS&. ANTHOZOA.
CTENOPHORA.
GRADE B. Celomocela.

a. Groups which in the present state of knowledge must be regarded
as distinct Phyla.

PLATYHELMIA. NEMATOIDEA. MOLLUSC.

ECHINODERMA. CHATOGNATHA.

VERTEBRATA APPENDICULATA NEMERTINA.

including the Sub-Phyla including the Sub-Phyla
Hemichorda, Rotifera,
4 Urochorda, Cheetopoda,

Cephalochorda, Arthropoda.
Craniata.

B. Groups whose relationship to the above Phyla is at present obscure,
and are therefore provisionally treated as distinct Phyla.
MEsozoA. ACANTHOCEPHALA.
POLYZOA. DIPLOCHORDA.

celia,” the distinction which it was intended to indicate by contrast with
the term “ Pseudoccelia” is no longer defensible. And, inasmuch as the
_Hertwigs themselves also use the term “ Ccelenteraten” in their “‘ Celom-

theorie” for the lower grade of Enterozoa, it seems inadmissible that they

should apply a word compounded of the same factors (enteron and koilos)
to a totally different set of animals. “Enteroceelomia” and “ Pseudo-
celomia” would more truly have expressed their meaning than the
words they employed. The cavity which they discuss in their book is
called “the ccelom,” not “the cc.”

}

é

\

1
4

6 ORGAN-SYSTEMS COMPARED

6. CHreF ORGANS AND ORGAN-SYSTEMS OF ENTEROC@LA AND
Ca@LoMoceé:LA.—Leaving out of consideration special locomotive
and prehensile mechanisms, and confining our attention to
differentiations of structure corresponding to important physio-
logical processes in the animal economy, we note in comparing
Enterocela and Ceelomoceela that it is by no means merely in
the possession of the ccelom that the latter grade rises above the
former. In all but the simplest Coelomoccla (the Platyhelmia
and some few minute forms) we find a BLOOD-VASCULAR SYSTEM,
consisting of main arterial and veinous trunks connected by rami-
fying capillaries, present. In rare instances only are the fine
capillaries absent, and their place taken by larger trunks. The
essential element of this system is a modification of a primary
tissue similar to the embryonic connective tissue of Vertebrata.
Its distinctive character is that the constituent cells form elongated
fibre-like groups, branching and constituting a reticulum, whilst
at the same time the cell-substance, instead of giving rise
to fibrillar skeletal material, becomes liquefied axially. Thus
tubes consisting of rows of elongated nucleated cells are formed
containing a highly organised liquid, which is often coloured red
with hemoglobin, and contains the nuclei of disintegrated cells,
which were the sources of the hemoglobinous fluid, as in
Cheetopoda and some Mollusca (Planorbis) and some Arthropoda.
On the other hand, the fluid may be colourless, whilst in it float
hemoglobinous corpuscles, as in Vertebrata, some Mollusca (Solen
legumen, Arca), and some Echinoderma, or the fluid may not only
itself be colourless but contain only colourless floating corpuscles
(most Molluses, Arthropods, and Echinoderms).

RENAL EXCRETORY ORGANS specially developed in the form of
sacs (renal sacs) and tubes (nephridia) are found in the Ccelomo-
ccela, whilst in the Enteroccela, although some cells or even cell
groups appear to have a renal excretory function—that is to say,
to be concerned in the elimination of nitrogenous waste—there are
no definitely constituted renal organs.

THE REGIONS AND GLANDULAR APPENDAGES OF THE ALIMENTARY
TRACT are, except in the Platyhelmia, very differently developed
in the Enteroccela and Ceelomoceela. A stomodeum (c7dpa, the
mouth, and ddaiov, adj. form of 686s, a road) results from a tube-
like in-pushing of ectoderm in the first formation of the mouth in
higher Enteroceela, In the Ccelomoceela we not only get a
stomodzum, but an ectodermal proctodeum (zpwxrds and ddaiov)
is similarly formed in connection with the anus, which is rarely
absent in that grade, and never present in the lower.

Paired digestive glands of various kinds, having the form of
saccular outgrowths of the gut, are present in most Coelomoceela,
and never found in Enteroccela.

——

‘

‘a Ocean tenance a aang atm
er eee eee ell

ORGAN-SYSTEMS COMPARED 7

a

ss

__ The ceelom in all but the lowest Ceelomoceela has by its large
development led to a very marked separation of the body-wall and
the gut-wall, and a consequent independent development of elaborate

SYSTEMS of MUSCULATURE in each of these superimposed regions.
In the Enteroccela there is no separation of body-wall-musculature
and gut-wall-musculature (nor in Platyhelmia, Nemertina, and
Nematoidea among Ccelomoccela).

The SENSE-ORGANS of the Enteroceela attain in some cases a
high degree of complexity (optic and auditory structures), but
the nerve tissue remains even in the highest to a large extent
diffuse, and in the form of a widely scattered network, though
ring-like concentration corresponding to the form of the body is to
some extent found. In the Celomoccela, even among the lowest,
a concentration of the nerve ganglion cells to form the CENTRES of
a NERVOUS SYSTEM is observed. Various steps in this concentra-
tion in the form of longitudinal cords may be observed in lower
and higher Ceelomoccela, tending to extreme concentration of the
nerve-ganglion-cells, and the protection and special nourishment
of the brain and nerve cord so produced.

BRANCHIAL RESPIRATORY ORGANS are frequently developed as
feather-like outgrowths or other modifications of the surface in
Celomoceela. The blood-vessels are distributed in these branchiz
and there receive oxygen, and liberate carbonic acid. In the
Enteroccela, the absence of a vascular system is accompanied by
the absence of special branchial organs.

In GENERAL FORM and SYMMETRY, as well as in the manifesta-
tion of merogenesis, or repetition of parts, the Enteroccela and
Ccelomoccela differ greatly. In both a primary bilateral symmetry
can be (with a few exceptions among the Enteroccela) detected.
But in the Enteroccela this is masked by a dominating tendency
to radial symmetry. Such masking of the more primitive bilateral
symmetry is rare in Coelomoccela, where, however, it is exhibited
by most of the Echinoderma.

MEROGENESIS.—The Enteroccela frequently give rise to lateral
buds, and so to arborescent growths, consisting of many individuals.
The Ccelomoceela more rarely produce lateral buds (Polyzoa,
Tunicata). The Coelomoccela often give rise to chains of complete
or incomplete individuals by growth, along the oro-anal axis, and
partial or complete division at right angles to that axis (meta-
meric segmentation). An apparently similar process is seen in the
segmentation and division of the Scyphistoma polyp at right angles
to the oro-aboral axis.

The exact historic relationship of metameric segmentation and
repetition of parts in the Colomoccela to a previously complete
production and separation of metameric “ buds ” or new individuals,

_ requires special consideration in each group of animals in which

8 ORGAN-SYSTEMS COMPARED

metameric segmentation is observed, or even but partial traces of
it, can be discovered. Whilst it is certainly not necessary to
suppose that metameric segmentation is actually derived from an
arrested formation of strobilated buds which at one time were set
free, it is nevertheless tolerably certain that the fundamental
property of the organism is the same in both cases, bud-strobilation
and metameric segmentation, and that whilst (whether it takes
the form of antimerism or metamerism, or paramerism) we may
indicate the exhibition of this property by the name “ merogenesis,”
we can, with advantage, distinguish the clear and well-marked cases
of repetition of “meres” as “eumerogenesis” (e.g. Lumbricus and
Teenia, Agalma and Eudendrium), whilst the blurred and obstructed

cases, such as are furnished by the Vertebrates, the Chitons, the

Nemertines, and the imperfect antimeres of Holothurians are
spoken of as cases of “dysmerogenesis.” The cases of eumero-
genesis are divisible into those resulting in separation, with or
without completion of parts, and those persisting as aggregations
with more or with less completeness and differentiation of the
“meres.”

The cases of dysmerogenesis are more difficult to analyse.
Their obscurity and incompleteness may be due to re-integration
following upon an earlier historical condition of eumerogenesis,
of which there is now no direct evidence (Chiton, Nautilus), or
they may be cases in which merogenesis sets in at an early stage
of individual growth and development, but has never in any
ancestral form persisted into adult life. In the last-named cases
merogenesis has never been more than a transient phenomenon
affecting the early stages of the individual, though it leaves
obscure and puzzling results of its existence which persist even
when full development is attained (? Vertebrates).

7. CONCERNING THE Ca@:LOM.
(a) Its historic definition.

We designate by the name “ ccelom” the cavity in Vertebrate
animals often called the pleuroperitoneal cavity, to which Haeckel
(see historical note below) originally applied the name, and for
which he invented it. We further, as a necessary result of mor-
phological theory, designate by the same name ‘“cclom” the
cavity or organ in other groups of animals which we consider to
be genetically identical with the primitive pleuroperitoneal cavity
of Vertebrates. “Colom” is not a term to be used for any and
every body-cavity other than the gut (as some eminent writers
seem to suppose), but definitely designates a morphological element

THE CQ@LOM 9

of high importance. The numerous embryological and anatomical
researches of the past twenty years seem to me to definitely
Testablish the conclusion that the celom is primarily the cavity,
from the walls of which the gonad cells (ova or spermata) develop,
‘or which forms around those cells. We may suppose the first
~ ecelom to have originated by a closing or shutting off of that
_ portion of the general archenteron of Enteroceela (Coelentera)
in which the gonads developed as in Aurelia or as in Cteno-
phora. Or we may suppose that groups of gonad mother-
cells, having proliferated from the endoderm, took up a position
between it and the ectoderm, and there acquired a vesicular
arrangement, the cells surrounding a cavity in which liquid
accumulated.

It is not of importance for our present purpose to decide be-
tween these two possible origins. They only differ in the earlier
or later development of the cavity which the gonad mother-cells
surround,

_In whichever of these two ways the cavity took its origin as a
separate chamber distinct from the archenteron, it was a ccelom,
a primitive elementary cclom, and originated from the cells of
- the archenteric wall.

Probably more than one pair of such cceloms were formed in
the primitive Coelomoccela, and by their fusion (as occurs in the
ontogeny of animals with paired ceelomic pouches) gave rise to

larger continuous cavities.

The ccelom is thus essentially and primarily (as first clearly

formulated by Hatschek) the perigonadial cavity or gonocecel,
and the lining cells of gonadial chambers are ccelomic epithelium.
In some few groups of Ceelomoccela the cceloms have remained
‘small and limited to the character of simple gonoceels. This
seems to be the case in the Nemertina, the Planarians, and
other Platyhelmia. In some Planarians they are limited in
number and of individually large size; in others they are
numerous.

In the great majority of Celomoccela the ccelom has vastly
extended its area and acquired secondary functions and a leading
importance in the physiology and architecture of the animal. In
the adult Echinoderma and Vertebrata, the ccelom is (omitting
secondary divisions) a single cavity of very large size, extending
in every direction between the body-wall and the gut-wall, and
occupied by a_ specialised fluid—the ccelomic fluid. In the
Cheetopoda it has attained to similar dimensions and is distended by
liquid so as to produce tension in the body-wall. In the Arthropoda
(which are now generally regarded as traceable to Cheetopod-like
ancestors) the ceelom has shrunk back again to relatively small
_ dimensions. It exists in them as the cavity of the gonadial sacs

¥
.
~

10 PHLEBGDESIS

and of certain excretory organs only.!_ There is reason to believe
that this small size of the celom in the Arthropoda is not due_to

a retention of the original small size of the coelomic sacs, but is

to be ascribed to a swelling of another and independent liquid-

holding cavity, namely, the blood-vascular or hemal system which
has filled up the space formerly occupied by a capacious ecelom.

(b) The theory of Phlebedesis—the Celom and the Hemoceel.

This swelling of the peripheral portions of the hemal system
may be called PHLEBGDESIS, and the lacunar blood-holding spaces
resulting from it form a ‘‘ Hemoccel” which has no connection
with the ccelom, but has to a large extent encroached on the space —
which once was occupied by ccelom and caused the reduction of
that organ to perigonadial and epinephric remnants. ;

In the Mollusca the ccelom also appears to have undergone re-
duction in volume. The pericardial cavity and the more or less
extensive ramifications connected with it, as well as the gonadial
sacs, are the ccelom of Molluses. Until recently (1885) it was —
erroneously supposed that the pericardial system of the Mollusca .
contained blood. It does not; it is, on the contrary, entirely dis-
tinct from the blood-system. In the more primitive Molluses
(some Neomeniz and Cephalopoda) the pericardial and perigonadial
sections of the ceelom are in continuity, and in them also the
blood-system appears more completely developed in the form of
cylindrical tubes or “vessels” than in other Molluscs. But in all —
Molluses as in all Arthropoda? the process of Phlebcedesis has |
taken place, and a voluminous, irregularly distended system of
blood - spaces—a Heemoccel—has suppressed and replaced to a
large extent the ccelom. In Lamellibranchs the paired, widely
ramifying tubes of the organ of Keber, leading out of the peri-
cardial ccelom, appear to be the reduced representatives of a
formerly voluminous ccelom.

It appears that neither in Arthropoda nor in Mollusca is
there any breaking through of the swollen blood-cavities into the
ccelom.

Before the theory of Phlebcedesis was established, it was
supposed by many zoologists (of whom I was one) that the ccelom
and blood-system were of one common origin, and that in Mollusca
and Arthropoda they were in open continuity, and, in fact, to a
large extent undifferentiated. This has now been shown to be an
erroneous view: the ccelom is distinct from the vascular system in

1 Possibly other remnants of the ccelom exist as spaces in connective tissue.
* It remains to be ascertained whether the Copepod Crustacean Lernanthropus
with its tubular vascular system containing red blood is an exception or not.

HAEMOCGL AND C@LOM II

origin and essential nature, and the two systems have not even

secondarily acquired a connection with one another in either
_ Arthropoda or Mollusca.

i

It is, therefore, very much to be desired that there should no

longer be any continuation of the confusion by the application of

the word “celom” to the blood-sinuses of Arthropods or of

~ Mollusca.

The independence of the origin of the “hemal system” or
“blood-vascular system” appears to be well established ; but
it is by no means so clear as to what is the history of the first
beginnings and subsequent development of the hemal system in the
animal series, as might be supposed. Whilst we are able to form
some conception of the probable history of the vicissitudes of the
ccelom from its first appearance to its present condition in the
various phyla of Ceelomoccela, we find that few, if any, attempts
have been made to trace out the history of the hemal system
in the same series. It is probable that it is one and the same
morphological entity, which we recognise as the blood-vascular
system or hemal system, in Vertebrata, Mollusca, Arthropoda,
Chetopoda, Nemertina, and Echinoderma. Its function is essen-
tially the absorption and distribution of chemical substances im-
portant in the life of the tissues, among the first of these being
oxygen gas. How could such a system originate? As ramifying
capillary channels or as simple longitudinal trunks? It is certain
that the walls of simple blood-vessels, and the blood itself, are
closely related in nature to the connective tissues, and in some
cases they have been shown to be developed from such tissue.
Possibly the earliest vascular system was preceded by solid rami-
fying cords of connective tissue, which performed absorptive and
distributive chemical functions even though not yet tubularised
and differentiated into liquid content and enclosing wall. We
have no conclusive reason for supposing that the hemal system
must have taken origin within the grade of Celomocela. It is
quite possible that we have to look for its origin in the lower
grade of Enterozoa—the Enterocela. This is a subject upon
which much speculation is possible, but to which little serious
attention has as yet been given. ‘That the hemal system is
connected in origin with a space which often arises between the
two primitive cell-layers of the embryo (the blastoccel) has been
suggested on the ground of certain embryological observations,
but the embryological facts are not in themselves conclusive as
to the ancestral arrangements of the parts in question. This
question is further considered below under the section “ Ccelom and
Mesenchyme.”

12 C@LOM AND BLOOD- VESSELS

(c) Intercommunication of Calom and Blood-vascular System. '

To return to the celom. Whilst there is no direct communi-
cation between that cavity and the hemal system in Arthropoda
or Mollusca, yet such a communication does occur in two import-
ant groups of Ccelomoccela. In the Vertebrata the lymphatic
vessels are in more or less direct communication with the ccelomic
cavity, and also open into the hemal system at more than one
point. The condition in Amphioxus, as described by Schneider, is
such as to give a very free communication between the vascular
system and the cclomic space at the base of the hepatic caecum.
It would be desirable that the existence of this connection in
Amphioxus should be inquired into again, though there seems to
be little doubt as to its existence.

Among the Chetopoda two very striking facts as to the fusion
of ceelom and hemal system have been recognised. The first is
the breaking up of the hemal tissue in Glycera and the Capitellide
in such a way as to result in the total disappearance of the hemal
system as a series of vessels whilst its cell-elements remain as
corpuscles coloured red by hemoglobin and floating in the coelomic
fluid. The second is the assumption in certain of the Leeches of
a canalicular form by a large part of the ccelom and the junction
of the canals so formed with the true hemal system by means of
capillaries. A remarkable fact is that portions of the ccelom (the
perigonadial portions) are shut off from this combination. We
thus obtain in the Leeches in question a uniform fluid, impregnated
in most cases with hemoglobin, circulating in vessels some of
which are of hzmal and others of ccelomic origin. The fact that
such a free intercommunication exists has been both asserted and
denied, but the most recent careful investigations (Goodrich, Quart.
Journ. Mier. Sci. 1899, vol. xlii. p. 477) leave no doubt that it really
obtains. So long as it was held that celom and hemal system were
one in origin, and that a fusion of the two obtained in Mollusca
and Arthropoda, the case of the Leeches did not appear singular.
But our present conception as to the complete independence of the
two systems in origin, and the knowledge that they do not inter-
communicate in either Mollusca or Arthropoda, renders it desirable
that we should have, if possible, a greater certainty than we have
at present as to the developmental origin of the channels which
are ascribed to ccelom in such Leeches as Hirudo. The evidence
appears to be in favour of their coelomic origin, but it is just
possible that they are not ccelomic. In Acanthobdella and also in
Clepsine (the former of which is to be regarded as an archaic form)
the hemal system is entirely closed and coexists with a well-
developed ccelom into which it does not open.

* ee
ee

C@LOM AND EXCRETORY ORGANS 13

(d) The Celom and Excretory Organs.

The physiological significance of an increase of size of the
original ccelomic sacs is not difficult to suggest. Whether in the
presence or absence of a hemal system the accumulation of a
quantity of organised liquid in cavities (or in a single cavity
formed by the fusion of two or more original coelomic sacs) must
have considerable physiological significance. The ccelomic fluid
and the ccelomic epithelium, as well as the floating corpuscles
derived from that epithelium, acquire special properties and im-
portance over and beyond the original functions subservient to
the maturation of the gonadial cells. The mechanical significance
of this liquid-holding chamber and its erectile function, similar to
the erectile function of the archenteric cavities in such Anthozoa
as the Pennatulids, are noteworthy; but the most important
developments of the ccelom are in connection with the establish-
ment of an exit for the generative products through the body-wall
to the outer world, and further in the specialisation of parts of
its lining epithelium for renal excretory functions.

In the Enterocceela the generative products either escape by
rupture of the body-wall outwardly, or are liberated into the
archenteron, and so escape by the mouth. Even in the Entero-
cela pores exist in many forms which permanently place the
peripheral parts of the archenteron in direct communication with
the exterior ; but these pores do not serve as passages for the
generative products (aboral pore of Peachia, tentacle pores of
Actinians, and polar pores of Ctenophora). Though in some
cases the generative products of the Ccelomocela escape from the
’ eelom by rupture of the body-wall, yet the existence of paired
apertures right and left, serving for the exit of the genital pro-
ducts from the coelomic sacs, must be regarded as a very early
feature in the history of the Ccelomocela. These apertures are
not formed by an invagination of the ectoderm, but by an out-
ward, often tube-like growth of the ccelom itself. They become
specialised in many groups in the form of more or less coiled
canals, and require to be recognised by a distinct name. I propose
to call them ccelomoducts.!_ Frequently they are furnished with
trumpet-shaped or funnel-like internal mouths. Such funnels are
termed coelomostomes. They exist where the cclom is large and
spacious, and the gonad (ovary or spermary) is not specially en-
closed in a duct-forming sheath, shutting it off from the rest of
the ccelom (a shutting-off which does take place in the Leeches
and Eudrilid Earthworms, and also in Echinoderms and many

1 There is no convenient Greek equivalent for “duct,” and I hold that we are

therefore justified in coining such hybrid words as “ ccelomoduct,” “ gonoduct,” and
“uroduct.”

14 C@LOM AND EXCRETORY ORGANS

2

Teleostean Fishes). Such funnel-like ccelomostomes are developed
on the ccelomoducts of the ovarian and spermarian segments of
the Earthworms and in many Chetopoda, also in Vertebrata
(peritoneal funnels of the reno-genital system) and in some Mollusca
(reno-pericardiac funnels). The ccelomoducts and the gonoceels, —
of which they are a part, frequently acquire a renal excretory
function, and may retain both the function of genital conduits and
of renal organs, or may, where several pairs are present (meta-—
merised or segmented animals), subserve the one function in some
segments of the body, and the other function in other segments. —
Again in some Mollusca (Gastropoda) it appears that the renal
function may be developed by the ccelomoduct and gonoccel
of the right side, and the oviducal or seminiducal function by —
those of the left side of the body. This very general assumption
by some or all of the primary gonoccels and ccelomoducts of renal —
excretory functions has led to a confusion of these structures
with the primitive ectodermal excretory tubes, which are best —
distinguished by the name “ nephridia.” The typical “nephridium” —
to which the name was originally given (see Lankester, Quart.
Journ. Micr. Sci. 1880), is the so-called “segmental organ” of the
Earthworm. This occurs as a pair of minute coiled tubes in each
segment of the worm’s body. Nephridia are distinguished by
their independent origin, each from a single superficially placed
cell which often is seen to be derived from ectoderm, and probably
must be traced to that layer even when it appears as part of the
mesoblast. They are also distinguished by their structure, which
is primarily that of a number of perforated or drain-pipe cells,
placed as it were end to end. It is not necessary to suppose that
this uniserial cellular structure is absolutely diagnostic of nephridia,
but it seems not improbable that it is so.

Instead of being, as was supposed, the common origin of
the renal organs of all the Ccelomoccela, it now appears (see
especially Goodrich’s series of memoirs in the Quart. Journ. Mier.
Sci. 1897-1900) that the nephridia are a primitive form of
excretory organ which have been replaced in the higher groups
of Ceelomoceela by uropoétic coelomoducts. True nephridia are
only found in the Platyhelmia, Nemertina, Rotifera, Chatopoda,
and in embryonic Mollusca (primitive kidneys of Pulmonata and
Lamellibranchia).

The tubular organs, whether renal or genital in function, which
have been identified of late years (by myself and others) with
nephridia, such as the kidneys of Mollusca, the segmental excretory
ducts of Peripatus, the genital and excretory ducts of Arthropods,
and the peritoneal funnels and tubules of Vertebrata, are all
ccelomoducts and not nephridia in the true sense of that word.
A very special cause of the error of those who first attempted to

HISTORY OF THE TERM CQ@:LOM 15

blish a theory of the uniform origin of the renal organs in
all Ceelomoceela from nephridia, is that the nephridia, though
primarily superficial and ectodermic, do acquire an internal open-
ing into the ceelom in the Chetopoda. The funnel-like internal
mouth (nephridiostome) which they often but not always develop
under these circumstances is part of the same chain of cells which
form the nephridial tube. Moreover, Goodrich has shown that the
nephridia which thus penetrate to the cceelom in Chetopoda,
may acquire most intimate relations to the ccelomoducts and their
celomostomes. In the marine forms (Polycheta) this associa-
tion leads to the formation of complex organs consisting partly
of ccelomoduct with ccelomostome and partly of nephridium.
These remarkable facts have only recently come to light, and
readily explain the confusion which has hitherto prevailed between
the ectodermal nephridia and the ccelomic ccelomoducts.

8. THe HISTORY OF THE TERM C@LOM AND THE THEORIES
CONNECTED WITH IT.

(a) From Haeckel, 1872, to the Hertwigs, 1881.

The word “ccelom” was introduced into morphological science
by Haeckel in 1872. In the first volume of his “ Kalkschwimme,”
p- 468, Haeckel writes as follows :—“Die wahre Leibeshéhle welche
bei Vertebraten gewohnlich Pleuroperitonealhéhle genannt wird,
und fiir welche wir statt dieses neunsylbigen Wortes die
bequemere zweisylbige Bezeichnung Coelom (75 xko‘Awpa, die
Hohlung) vorschlagen, findet sich nur bei den héheren Thierstam-
men bei den Wurmern, Mollusken, Echinodermen, Arthropoden
und Vertebraten.”

According to the theoretical conception which was justified by
the imperfect knowledge of embryological facts of that time,
Haeckel regarded the ccelom as a space formed by a “split” in
the blastoderm dividing the middle cell-layer into two secondary
layers. According to this view the outer of these, the dermal
fibrous layer (Hautfaserblatt), adheres to the ectoderm to form
the fibrous and muscular layer of the body-wall; the inner, the
intestinal fibrous layer (Darmfaserblatt), adheres to the endodermal
lining of the gut to form the fibrous and muscular part of the
gut-wall. It was natural and justifiable to provisionally identify
with the Vertebrate split-spacé thus formed and distinguished as
“the ceelom” the chief cavity lying between gut-wall and body-
wall in Mollusca and Arthropoda, as well as the similarly situated
cavities of Chetopoda and Echinoderma. The hypothesis as to
the origin of the ccelom was that it was formed by the accumula-
tion of nutrient fluids which passed through the wall of the
alimentary canal. Thus Haeckel erroneously identified the dis-

—~

THEORIES OF THE C@LOM

tended blood-spaces of Mollusca and Arthropoda with the
Vertebrate ccelom, whilst he correctly identified with it the great
body-cavities of Cheetopods and Echinoderms.
The word “ccelom” was adopted by Haeckel’s friend and
colleague in the University of Jena, Carl Gegenbaur. In the
second edition of his masterly treatise, the “Grundziige der ver-
gleichenden Anatomie” (English edition 1878, p. 367), Gegenbaur
says in regard to the ccelom of Mollusca: “As a’ rule the vascular
system is freely connected with the ccelom, which therefore forms
a portion of the hemal system.”
And again, in relation to the ccelom of Arthropoda, he writes
(p. 278 of the same work): “The ccelom is found in all the
Arthropoda, and forms a portion of the blood-vascular system, so
that the peri-enteric fluid found in many Vermes as a fluid differen
from the blood, is represented in
the Arthropoda by the blood
itself.”
The first of the series of observa-
tions, which have ultimately led
to a view as to the essential nature
of the ccelom different from tha
of Haeckel and Gegenbaur, already
existed before the word ccelom
itself was coined. As far back as —
1864 Alexander Agassiz (Embryo-
logy of the Starfish, in Contri-
butions to the Natural History
of the United States, vol. v. 1864)
showed in his account of the de-
velopment of Echinoderma that
the jgreat body-cavity of those
animals developed as a pouch-like
Fic. 4.—Lanva or Bataxociossus ix outgrowth of the archenteron of the
SAGITTAL Srorion TO SHOW THE acc embryo (see Fig. 2) whilst a second

oF THE Ca:Lom AS TAREE PAIRS OF ‘ :
LESTE DRE TRE outgrowth gave rise to their ambul-
Cy, anterior, Cu, middle, Cr, posterior acral system ; and in 1869 Metsch-
pairs of cclomic pouches ; d, archen- nikofft (Mem. de l’Acad. Imperiale
Se eaaery Bateson, from Korschelt’ des Sciences de St. Petersbourg,
series vii. vol. xiv. 1869) con-—
firmed the observations of Agassiz, and showed that in Tornaria
(the larva of Balanoglossus) a similar formation of body-
cavities by pouch-like outgrowths of the archenteron took
place (Fig. 4). Metschnikoff has further the credit of having, in
1874 (Zeitsch. wiss. Zoologie, vol. xxiv. p. 15, 1874), revived
Leuckart’s theory of the relationship of the ccelenteric apparatus
of the Enterocela to the digestive canal and body-cavities of

THEORIES OF THE C@LOM 17

higher animals. Leuckart had in 1848 maintained that the
alimentary canal and the body - cavity of higher animals were
united in one system of cavities in the Enteroccela (Verwandtschafts-
verhiltnisse der wirbellosen Thiere, Brunswick, 1848). Metschni-
koff insisted upon such a correspondence when comparing the
Echinoderm larva, with its still continuous enteron and ccelom, to
a Ctenophor, with its permanently continuous system of cavities
and canals. Kowalewsky in 1871 showed that the body-cavity of
Sagitta was formed by a division of the archenteron (Fig. 5) into
three parallel cavities, and in 1874 demonstrated the same fact for
the Brachiopoda (see Fig. 3).

In 1875 (Quart. Journ. Mier. Sci. vol. xv. p. 52) Huxley
proposed to distinguish three kinds of body-cavity : the schizoccel,

Fic. 5.—Turee Staces (A, B, C) IN THE DEVELOPMENT OF SAGITTA TO SHOW THE ORIGIN
OF THE CazLoM As A PAIR OF ENTEROCGLOUS POUCHES.
m, mouth; al, alimentary canal; ae, archenteron ; bl.p, blastopore; pv, coelomic pouch ;

80, sp, epithelial wall of the same pouch ; ge, gonad cells. (After Butschli and Kowalewsky,
from Balfour.)

formed by a splitting of the mesoblast, as in the chick’s blasto-
derm ; the enterocel, formed by pouching of the archenteron, as
in Echinoderms, Sagitta and Brachiopoda; and the epicel. This
last name he applied to the atrial chamber of Tunicates and to
a supposed chamber in Amphioxus, the existence of which he was
led to believe in, by the examination of ill-preserved specimens.
Immediately after this I put forward the theory of the
uniformity of origin of the ccelom as an enteroccel (Quart. Journ.
Mier. Sci. April 1875). I pointed out that inasmuch as it had
been shown in many cases that the mesoblast is derived from the
hypoblast (wall of the archenteron), it might well be supposed
that the splitting of the mesoblast is only a delayed formation of
the /wmen of the enteroccelous pouch: that in fact the mesoblastic
somites and solid paired masses are only enteroccel pouches in a
solid condition, destined after a brief delay to open out as pouches
or sacs. My theory of the celom as an enteroccel was accepted
2

18 THEORIES OF THE CG@:LOM

by Balfour, and was greatly strengthened by his observations on
the derivation of both notochord and mesoblastic somites from
archenteron in the Elasmobranchs, and by the publication in 1877 —
by Kowalewsky of his second paper on the development of —
Amphioxus—in which the actual condition which I had supposed
to exist in the Vertebrata was shown to occur (see Figs. 6, 7, and
8), namely, the formation of the mesoblast as paired pouches in
which a narrow lumen exists, but is practically obliterated on the —

Fic. &. 4

Fics. 6, 7, 8. TRANSVERSE SECTIONS OF
THE Bopy OF THREE LARV2 OF
AMPHIOXUS AT SUCCESSIVE STAGES
OF DEVELOPMENT IN ORDER TO SHOW
THE ORIGIN OF THE C@LOM AS
PAIRED ENTEROCGLOUS POUCHES.

Fic. 6 shows the celomic pouches
(Ih) as part of the enteric wall.

Fic. 7 shows them nipped off as —
closed sacs,

Fic. 8 shows them pushing their
way between ectoderm and endoderm ;
the right-hand sae has divided into an
upper ‘‘ myoceel” and a lower “‘ splanch-
nocel.” ak, ectoderm, ik, endoderm,
mk, mkl, mk?, epithelium of the cc-
lomic wall ; lh, ccelom ; mp, foundation
of the nerve cord; n, nerve cord; ch,
notochord ; us, myoccel ; dh, gut. (After
Hatschek, from Hertwig.)

nipping off of the pouch from the archenteron, after which process
it opens out again as ccelom.

The chief difficulty which my theory of the uniform nature of
the ceelom had to encounter was in bringing the cavities con-
sidered to be “ccoelom” in the Mollusca and the Arthropoda into
thescheme. At this time I accepted, in common with most embryo-
logists, the view of Haeckel and Gegenbaur, that the irregular —
and more or less spongy space holding blood in those animals is
in reality the coelom, and as a part of that interpretation I accepted
the theory that the blood-vascular system is itself only a part of
the celom cut off from it and specialised in most cases, but con-

. THEORIES OF THE CQ@LOM 19

fluent with it in the Mollusca and the Arthropoda. Guided by
this erroneous view, I suggested that the reduction of the entero-
ecelous pouches of mesoblast might proceed further than solidifica-
tion; the process of simplification might well be supposed (I
suggested) to go on to the reduction of the number of the cells
detached from the archenteric wall, so that eventually a ccelom

Fics. 9, 10, and 10bis.—TuREE VIEWS OF A YOUNG
EMBRYO OF THE MOLLUSC PIsIDIUM PUSILLUM.
Fic. 9 Is VIEWED FROM THE SURFACE AND SHOWS
THE EcroperMAL (epiblast) Crxus. Fic. 10
SHOWS THE SAME EMBRYO IN OpTicAL MEDIAN
SECTION, WHILST Fic. 10bis SHOWS A FOCUSSING
TO A PLANE JUST BELOW THE EPpIBLASTIC LAYER.

The invaginated archenteric sae (hypoblast) hy
is seen at one pole. Closely applied to the under
surface of the epiblastic layer are numerous branched
cells, me; similar cells (p) appear to be originating
by cell-division from the wall of the archenteron.
The cells me and p are ‘“‘mesenchyme.” Possibly
ainong them, near to the archenteric wall, are the
mother-cells of the ccelomic pouches. (After Lan-
kester, from Balfour.)

Fic. 10. Fic. 10bis.

might be formed by a few wandering cells, or even a pair only of
such cells, detached from the archenteric wall, and creeping over the
ectoderm and endoderm in the space between them which often is
enlarged to form a blastocel. Such cells do occur in Mollusca
(Cyclas,! Lymneus, Paludina), and probably have to do with the
formation of blood-vessels and blood and other skeleto-trophic tissue,
though their history has not been traced (see Figs. 9, 10, and 10bis).

» 1 See Lankester, ‘‘ Development of Mollusca,” Phil. Trans. 1873.

fb

20 THEORIES OF THE C@LOM

It is, I think, now certain that they have nothing to do with the
formation of coelom. 7
On the other hand, later researches, ¢.g. those of Hatschek on
Polygordius (see Fig. 11), have confirmed the important view,
which I deduced from Kowalewsky’s account of the origin of
the mesoblast in Lumbricus, namely, that the first rudiment of -
the ccelom, instead of detaching itself from the archenteron as_
a pouch or even a solid mass of cells about to split, may separate
from the archenteric epithelium as a single pair of cells, which”
take up their position in the blastoccel (space between ectoderm —
and endoderm) in this state of naked simplicity (Fig. 11, 4), and

4
|
|
f

=
J
3

ey

8/8,

Se —————

Fic. 11.—TRANSVERSE SECTIONS OF THE LARVA OF THE CH&TOPOD POLYGORDIUS TO SHOW —
THE ORIGIN OF THE CazLoMIC PoucHES FROM TWO PRIMARY CELLS DETACHED FROM THE —
ARCHENTERIC EPITHELIUM.

A, section of an unsegmented larva, just in front of the anus, showing ect, ectoderm, —
end, endoderm, and mes, the two primary mother-cells of the ccelom. 2B, section of an —
older larva near the tail. mes, the coelomic rudiments formed by the division and growth —
of the primitive ccelomic cells; n, forecast of the nerve cord. C, section of the same larva
nearer the head. The splanchnic (sp) and somatic (so) walls of the ccelom have diverged
from one another forming the eccelomic cavity. mn, forecast of nerve cord. (After Hatschek,
from Korschelt and Heider.)

then proceed to multiply so as to form a solid mass of cells right —
and left (Fig. 11, 6), and finally open out as two well-developed _
ccelomic sacs (Fig. 11, C). This is a fine typical instance of
“ precocious segregation,” the original right and left ccelom cella
moving away from their proper and ancestral position in the~
series of archenteric wall-cells at an astonishingly early period,
instead of waiting until they have formed a complete ecelomic
sac,

The first important attack upon the theoretical identification
by Haeckel, Gegenbaur, and myself of the blood-space of Mollusca
with the celom is due to the brothers Hertwig, who in their

+ THEORIES OF THE C@LOM 21

‘interesting work, Die Ccelomtheorie (Jena, 1881), definitely denied

to this space the nature of celom. They called it “ pseudoccel,”
‘and in the same category they placed the body-cavities of the
Rotifera, the Polyzoa, and the intercellular spaces of the paren-
chyma of Platyhelmia. The remaining groups of animals (exclusive
of the Ceelentera of Leuckart) they credited with the possession of
a true ccelom, which they considered as being always an entero-
ecel in origin.

The Hertwigs thus practically accepted my theory of the origin
and nature of the true ccelom, but rightly refused to include in
this category the blood-holding space of the Molluscs. If I proceed
to point out where they were mistaken it is in no spirit of
reproach, for their work has in this and again in the history of
the fertilisation of the egg-cell been of capital importance. It is
necessary, as we push our way through the dark, to make mistakes
and entertain erroneous hypotheses which, with the increased know-
ledge of fact due to the work of a vastly increased body of
observers, give way to new conceptions in accordance with our
improved understanding of the phenomena before us.

The Hertwigs failed to recognise the existence of the true
“cecelom” in Mollusca, viz. the pericardial, perigonadial, and renal
sacs. Further, they did not recognise that the cavitary system, which
they called “ pseudoccel” in Mollusca (with, it is true, considerable
reservation as to its actual nature), is merely the blood-vascular
system in a swollen condition. They also associated under the
name “ pseudoccel” various spaces in other animals which have
nothing in common with one another or with the hemoccel of
Mollusca: Lastly, they maintained (as it now appears erroneously)
the ccelomic nature of the hemoccel of Arthropoda as taught by
Haeckel and Gegenbaur, and as at that time accepted by me.

The Hertwigs, in the historical retrospect at the close of their
volume Die Ccelomtheorie, pay generous tribute to the work of Eng-
lish anatomists in establishing a true theory of the celom. They
say: “Wahrend in England, wie uns der geschichtliche Ueber-
blick gezeigt hat, die Entdeckungen von Agassiz, Metschnikoff und
Kowalewsky auf einen fruchtbaren Boden gefallen waren und Mor-
phologen wie Huxley, Lankester und Balfour zu weittragenden
und zum Theil gliicklichen Speculationen veranlasst hatten, ist auf
diesem Gebiete in Deutschland keine Bewegung in das Leben
gerufen und eine Weiterbildung der besprochenen Theorieen nicht
versucht worden.”

(b) Progress in the Understanding of the Calom from 1881 to 1896.

Whilst the conception of the ccelom as essentially an entero-
cceelous pouch, nipped off from the archenteron, is admitted to be

22 PHLEBQ@DESIS AND HAMOCGL

due to English morphologists, the later developments of our know-
ledge as to what is and what is not “ccelom” are very largely due
to the same school. :

In 1881 I undertook an investigation of the blood-systems of
both Mollusca and Arthropoda, at that time held by me and by
nearly all other morphologists to represent ccelom, either in con-
sequence of the confluence of two systems at one time separated,
or by survival of an undifferentiated condition.

At that time the pericardium of the Lamellibranchia in par-
ticular, and of all other Mollusca by implication, was held to be a
blood space in communication by veins with the general blood-
system. In Anodon the apertures of these veins were pointed out
in text-books of Comparative Anatomy on the anterior wall of the
pericardium. I found that the fluid in the pericardium of Anodon
is not blood, and that the so-called apertures of veins on its wall
are the apertures of a remarkable branching tubular system (form-
ing, in large part, the organ of Keber, but extending far beyond
it). I found, further, that in Gastropoda the pericardium does
not contain blood. The red-blooded Lamellibranch, Solen (Cerati-
solen) legumen, which has oval corpuscles coloured by hemoglobin
in its blood, appeared to me likely to furnish a valuable case for the
study of this question. One of my pupils, Mr. Penrose (British
Association Reports, 1882), and subsequently I myself (Zoologischer
Anzeiger, 1884), examined Solen legumen in the living condition,
and also by means of sections, and established the fact that the
red blood never enters the pericardial chamber, and, further,
that no blood is exuded from the animal’s body (by pores or
otherwise) when it rapidly retracts the foot after previous
expansion. Other investigations which I had commenced in 1867
on the renal organs of Patella were resumed, and led me to the
conclusion that the pericardial space of Mollusca is not a blood
space, and that it is in communication with the renal sacs by
ciliated reno- pericardial apertures (often funnels) which lead
through the renal sacs (“urocels,” according to our present
nomenclature) to the exterior. I thus came to the conclusion that
the pericardial chamber (and its Keberian tubules in some Lamelli-
branchs), together with the gonad sacs, which in Neomenia and
Cephalopoda communicate with the former, are the real ccelom of
Mollusca. At first I adhered to the dominant theory that the
blood-holding space is also to be regarded as a part of the ceelom
but shut off from it. Buta subsequent consideration of the blood-
system of the Arthropoda, and of the fact that the more primitive
Mollusca (the Polyplacophora and the Cephalopoda) have well-
developed tubular blood-vessels largely developed, led me to put
forward the theory of Phlebeedesis. According to this theory,
the true celom is present in a reduced form in both Mollusca and

—_—_—

PHLEBQEDESIS 23

” HEART OF ARTHROPODA (on the right) FRoM THE DoRSAL VESSEL OF A
(From Lankester.)

” opening into the heart.

* ostia

&
.
Le

,

3

Cuxtopop (on the left), ACCORDING To THE THEORY OF PHLERGDESIS.

DIAGRAM TO SHOW THE ORIGIN OF THE ‘Os

/
>)
The veins entering the Chetopods dorsal vessel are supposed to become distended, and eventually to fuse with one another so as

to form the pericardial blood-sinus with its valvular

Fig. 1

\ 2
PS

| feos

ealled “ hemoccel,” which have been erroneously considered to be
_ parts of the ccelom, are in reality swollen blood-vessels.

24 C@LOMODUCTS IN ARTHROPODA |

A step precedent to the development of the theory of Phlebc- —
desis was the recognition of the fact that the green glands and
“shell glands” of Crustacea, the coxal glands of Limulus and
Scorpio, and the generative ducts of Arthropoda generally, belong
to that same system of ccelomic exits or ducts to which the renal
organs of Mollusca belong. To these we now give the name
“nrocels” and “cclomoducts” (see below as to this nomen-
clature), and distinguish them from the true nephridia of the
Earthworms and Platyhelmia, though they were until quite —
recently all spoken of by the one term “nephridia.” Various —
anatomists have contributed to the establishment of the fact that
the tubular glands at the base of the antennz in Crustacea are —
connected internally with a frequently very extensive cavity quite
distinct from the blood space (Marchal, Comptes Rendus, exi. 12,
and exi. 16; and Weldon, Quart. Jour. Micr. Sci. vol. xxxii. 1891,
p. 279; and Journ. Mar. Biol. Assoc. vol. i, New Series, 1889-90).
The gonadial sacs of Arthropoda, like the gonadial sacs of Mollusca,
must be regarded as representing a portion of the ccelom, and the —
cavity into which the other similarly placed ducts open is also in
all probability ceelom. The blood system need not, therefore (I
argued), be considered as in any way representing ccelom ; it is
probably only a dilated swollen blood-vascular system which has
“crowded out” a good deal of the pre-existing ccelomic chamber
or chambers. In 1885 I had arrived at these views, and indicated
them in a note to a paper by my pupil, Dr. Gulland, “On the
Development of the Coxal Gland of Limulus” (Quart. Jour. of
Micros. Sci. 1885, p. 515). At this time Mr. Adam Sedgwick, of
Cambridge, was working at the later stages in the development
of Peripatus, and early in 1887 announced to the Cambridge
Philosophical Society a discovery of the utmost importance in
regard to the whole question of the relation of ccelom and vascular
system in the Arthropoda. Mr. Sedgwick showed that the ccelom
of Peripatus capensis is developed as a series of paired cavities in
the mesoblastic somites derived from the wall of the archenteron.
These paired ccelomic cavities and the axial metenteric cavity are
at one time the only spaces to be observed in a transverse section
of Peripatus (Fig. 13, 4). The paired ccelomic cavities proceed
to divide each into a dorsal and a ventral portion (Fig. 13, C).
The dorsal portions form the perigonadial ccelom, whilst the
ventral portions give rise to the renal tubes and end sacs
(epinephric ccelom), which have hitherto been spoken of by Balfour,
Sedgwick, myself, and others as nephridia, but should no longer be
identified with the excretory tubes of Oligocheta and Platy-
helmia, to which the name “nephridium” was originally applied
by me, and for which alone it should be reserved. The renal
celomic tubes of Peripatus must be classed as “ uroccels,” pro-

—

Eo -

C@LOM OF PERIPATUS

vided with their own proper “ccelomoducts,” being excretory
modifications of the primary exits or ducts of the ccelom, which
served in the ancestral ccelomoceelous animal as exits for genital
products.

_ Whilst the dorsal divisions of the coelomic sacs of Peripatus
are moving upwards towards the mid-line of the back, a space

Fic. 18.—TRANSVERSE SECTIONS SHOWING THE BREAKING UP OF THE C@ELOM, AND THE
DEVELOPMENT OF THE HMOC@L IN PERIPATUS.

A, section of a young embryo, in which the only cavities present are 1, the gut or
metenteron, and 2, the ccelom in the form of a pair of pouches (in each segment) derived
_ from the wall of the primitive archenteron. B, section of a later embryo showing the
division of the coelom on each side into a dorsal and a ventral cavity (2, 2), and the
appearance of the hemoccel as three longitudinal cavities (8, 3, 3). C, section of a later
embryo; the dorsal cavities of the cclom have migrated to the dorsal mid-line; the
ventral sacs acquire such an opening to the exterior. D, section of a still later embryo.
The dorsal portions of colom (2) become the gonads (gonoccels); the ventral portions
{2') become uroccels with end-sacs (the so-called segmental organs usually, but errone-
ously identified with ‘‘nephridia”), The hemoccel shows a division into several com-
partments ; the heart (3’) has made its appearance. The nerve cords (4), already visible
in C, are well developed, and portions of the slime-glands (5) are seen in section. (After
Sedgwick, from Sedgwick’s Text-book of Zoology.)

begins to make its appearance between the body-wall and the gut-
wall, and rapidly increases in volume (Fig. 13, B, 3). This is the
blood-space or hemoceel. It is of very great importance that we
should have minute and repeated examination of the development of
this space in various Arthropoda, since light will thereby be thrown
on the primitive lines of historic development of the blood-vascular
system. From Mr. Sedgwick’s description of the origin and

26 C@LOM AND HAMOCGL

subsequent development of this space in Peripatus, there can cer-

tainly be derived some justification for the view (which has from —

time to time been expressed by various morphologists) that a space
between primitive endoderm and ectoderm formed by the accumu-

lation of liquid in that position, and spoken of as the “ blastoccel,” |

is the origin, the point of departure, so to speak, of the blood-
vascular system. We cannot, however, consider that this ques-
tion has been yet brought to a probable solution. Whatever its
ancestral origin, it is abundantly clear from Mr. Sedgwick’s draw-
ings and statements that the hemoccel thus formed is entirely
independent in its origin of the ccelom, with which it never
acquires any kind of connection. Observations tending to extend
Sedgwick’s discovery to the embryological history of Crustacea
and some other Arthropoda have been made since his publication
by other observers (see Allen, Quart. Jour. Mier. Sci. vol. xxxiv.
1893, p. 403).

At the meeting of the British Association in Manchester in
1887—having been confirmed by Sedgwick’s demonstration in the
speculations to which I had been led by the consideration of other
facts—I formulated a general theory of the origin of the hemoccel
of both Mollusca and Arthropoda by an excessive swelling of the
non-arterial portions of the vascular system which, in an earlier
ancestral form, had been provided throughout with tubular capil-

laries and veins. A report of this communication appeared in —

“Nature ” of March 1888, and was reproduced with some additional
remarks and a diagram (Fig. 12) used on the occasion of the
original communication, in the Quart. Journal of Micros. Science,
1893, vol. xxxiv. p. 427. This theory I now call the theory of
Phlebcedesis.

As stated in the paper above cited, the theory thus named is
as follows :—‘“ That the system of blood-containing spaces pervad-
ing the body in Mollusca and in Arthropoda is not, as sometimes
(and indeed usually) supposed, equivalent to the ccelom or peri-
visceral space of such animals as the Chetopoda and the Verte-
brata, but is in reality a distended and irregularly swollen
vascular system—the equivalent of the blood-vascular system of
Cheetopoda and Vertebrata.” The name hemoccel was proposed
by me for this phlebcedetic space or cavity, and was subsequently
adopted by Sedgwick in his detailed account of the development
of ccelom and blood space in Peripatus. At the same time I
showed from injections and silver impregnations of Anodon,
Cephalopods, Astacus, and Limulus, that true capillaries are in
certain regions of the body in both Mollusca and Arthropoda

more largely developed than is generally supposed. I showed —

that the far-spreading tubules of the organ of Keber in Molluses,
and probably also a system of spaces in the connective tissues of

PHLEBGQDESIS 1N CHA.TOPODA 27

_ Astacus and of Limulus, should be regarded as remnants of the

coelom, the bulk of which has been filled up by swollen blood-
‘yessels, leaving only epinephric and gonadial sacs in the Arthro-
poda, pericardial and gonadial sacs in the Mollusca.

Some years later my assistant, Dr. Benham, now Professor in
Dunedin, New Zealand, described (Quart. Jour. Mier. Sci. xxxix.
1896) a condition of the blood-vessels in the Chztopod Magelona,
which is parallel to that through which the vessels of ancestral
Molluscs and Arthropods must have passed. Phlebcedesis is carried

ae",

~~ 7 = = S
FONG 0¢ oF eS

> 2 _ Fe
SS BF 2
%o ‘ aco i
Niet agge gh ihe
: oo mr 9

cure. Vv.

Fic. 14.—Transverse SeEcTION OF THE THORACIC REGION OF THE CH#TOPOD MAGELONA
TO SHOW THE SWELLING OF THE BLOOD-VESSELS AND CONSEQUENT REDUCTION OF THE

CasLtom.

D.v, dorsal vessel; G, gut; N, nerve cord; V.v, ventral vessel greatly swollen,
filled with a peculiar corpusculated blood; Jat.ert, lateral extension of the same; ca,
ecelom; J.v, lateral vessel; J.m, longitudinal muscles; circ, circular muscles; _ obl,

oblique muscles ; dor.v.m, dorso-ventral muscle. (After Benham.)

to such a point in Magelona as to extinguish to a large extent
the proper ccelomic cavity (see Fig. 14). This observation seems
to be of importance as showing the tendency to Phlebcedesis in
Cheetopods among the ancestors of which the ancestors of both
Mollusca and Arthropoda are in all probability to be sought.
When we remember further that in some Chetopods the cells
which should form the blood-vessels and the blood, may actually
break up altogether and give rise to floating hzemoglobinous
corpuscles with a total absence of blood-vessels (Glycera and
_ Capitellide), we must admit that it is not surprising that the task

4

28 CE@LOMIC SACS OF MOLLUSCA

of tracing the origin and history of the blood-vascular system in
the animal series is a difficult one and full of pit-falls for the
speculative morphologist.

By the establishment of the existence of the ccelom in an
independent condition in Mollusca and Arthropoda, having so far
as embryological observations have gone, ‘an enterocclous origin
(von Erlanger in Paludina,! Sedgwick in Peripatus), and by the
recognition of the spaces at one time confounded with ccelom in
those great phyla, as being in reality swollen blood-vessels or

Fic. 15.—Youne Empryos oF THE GAsTROPOD MoLiusc BITHYNIA TENTACULATA TO SHOW
THE APPEARANCE OF THE CG:LOM AT AN EARLY PERIOD AS A PAIR OF POUCHES
DERIVED FROM THE WALL OF THE ARCHENTERON (? as solid or hollow outgrowths).

A, frontal section; B and C from the right side. a, region of the anus; dl, blasto-
pore; c, celom; mes, epithelial cell- wall of the ecelom; ent, endoderm; m, mouth ;
sd, shell-gland; t, prostomial region; v, cells of the ciliated band of the velum.
(After von Erlanger, from Korschelt and Heider.)

hemoceel, the theory of the ccelom is brought to a second stage.
The results thus emphasised have been gained during the fifteen
years which succeeded the publication in 1881 of the Hertwigs’
Celomtheorie. The existence and the unity of the cclom
throughout the animal series above the Protozoa and Enteroccela,
its derivation in all cases from pouch-like growths of the archen-
teron either actually or with delayed appearance of the lumen, as
suggested by me in 1875, seems now to be established with some-

1 See Fig. 15 and the explanation.

|

Aan nmsilagme

MESENCHYME AND MESOBLAST 29

thing like certainty ; and I venture to point out that this further
stage of progress, like the earlier which started from the first
generalisation of Haeckel of Jena, has been gained by the specula-
tion and observation of the English school of morphologists.

(c) The Celom and the Mesenchyme.

The recognition of the ccelom as a constant factor of the
bodily structure of the higher animal phyla, and of its essential
nature as a pair of enteroccelous pouches (or in lower forms as
possibly a single pouch, or several such pouches), gives the key
for the analysis of that mass of cells lying between the outermost
layer of the embryo (epiblast) and the innermost layer (hypoblast)
to which in Triploblastic animals, 7.e. animals with apparently
three embryonic cell-layers, the term ‘‘ mesoblast ” has been applied.

Clearly one factor of this ‘mesoblast” is the rudiment (fore-
cast, Anlage), of the ccelom, whether appearing as a pouch (Fig. 3),
or a solid mass of cells (Fig. 11, B), or as a single pair of cells
(Fig. 11,4). There are some reasons for supposing that the whole
mesoblast is thus accounted for, and that whatever cells appear
in the mesoblast outside and beyond the lining cells of the
ecelomic pouches are only secondary derivatives of the wall of the
celomic pouches. The development of Amphioxus, for instance,
seems to be satisfactorily traced to a folding of a sheet of cells,
arranged in a superficies one-cell-deep. Thus the embryonic tissues
of Amphioxus have a strictly epithelial character: the cells all
bound a surface. By a primitive infolding of the vesicular mono-
blastula (or one-cell-layered embryonic vesicle), we obtain the
archenteron; by a second elongated infolding the nerve cord ;
by an outgrowth of hollow folds from the archenteron, the primitive
ecelom is formed; and by subsequent foldings of the wall of this
chamber (as shown by Hatschek, Anat. Anzeiger, August 1888),
the myoccel and the splanchnoccel (divisions of the ccelom) are
formed. All the main tissues, muscular and skeletal, as well as
the tissues arising from the lining cells of the gut and from the
epiblast, have an epithelial origin; there is no accumulation of
cells in heap-like masses, no development of branching, irregularly
grouped series of cells overlying one another and filling up a space
between epithelial layers.

It may be argued accordingly from Amphioxus that, primarily,
the whole mesoblast in all cases is nothing but epithelial foldings
of the ceelomic pouches, and that any and all separate cells not
lying in the plane of the epithelial surface are merely due to
secondary detachment and wandering of a precocious character.
It is, however, to be noted that even in Amphioxus the formation
of the blood-vessels, large and small, and of the blood has not yet

30 MESENCHYME

been traced to an epithelial origin, that is to say, to a folding of

the original spherical envelope of the monoblastula, or of one of
its derivative folds.

The Hertwigs in Die Ceelomtheorie, p. 78, emphasise this distine-
tion in the origin of tissues. They point out that in some animal
groups a larger proportion of the adult tissues can be traced to
foldings of embryonic epithelia than in others. The irregular
heap-like groups of cells, which are not spread out as folds of
epithelial surface and so often form a large part of the “mesoblast”
of animal embryos, they speak of as “mesenchyme.” Iam inclined
to think that the distinction here made is useful. The mesoblast
of Celomocela consists of the epithelial fold of the ccelomic
pouch (or its representative cells) and of mesenchyme. The question
remains as to what is the origin of that mesenchyme. It cannot

Fic. 16.—GASTRULA STAGE
OF AN ECHINOID SHOWING
DEEP ARCHENTERIC INVA-
GINATION DEVOID AS YET
or Ca:Lomic PoucHES, BUT
WITH LARGE MESENCHYME
CELLS TRAVERSING THE
BiastoceL or Cavity
BETWEEN ECTODERM (epi-
blast) AND ENDODERM
(hypoblast). (After Se-
leuka, from Korschelt and
Heider.)

be considered as yet sufficiently ascertained to warrant a final
conclusion. According to observations made in some groups,
mesenchyme is largely derived from epiblast, in others from hypo-
blast (Fig. 16), in others its appearance in the blastoccel or space
of the primitive embryonic vesicle precedes the formation of archen-
teron itself (Fig. 17). I think that we are bound to bring into
consideration here the existence in many Ccelentera of a tissue
resembling the mesenchyme of Ceelomoceela. In Seyphomeduse,
in Ctenophora, and in Anthozoa, branched, fixed, and wandering
cells are found in the mesogleea which seem to be the same thing
as a good deal of what is distinguished as “mesenchyme” in Coelomo-
ccela. These appear to be derived from both the primitive layers ;
some produce spicules, others fibrous substance, others again seem
to be amcebocytes with various functions. It appears to be
probable that, though it may be necessary to distinguish other

at oo

|
:

MESENCHYME AND BLOOD- VESSELS 31

re)

elements in it, the mesenchyme of Ccelomoceela is largely consti-
tuted by cells which are the mother cells of the skeleto- trophic
group of tissues, and are destined to form connective tissue, blood-
vessels, and blood. The relation of the mesenchyme cells (as
shown in such cases as those represented in Figs. 9 and 10) to
the blastoccel or primary cavity of the blastula seems to favour
the notion that the blood-vascular system has originated from the
blastoccel in co-operation, so to speak, with mesenchyme cells.
Whether, as is most probable, the mesenchyme also gives rise to
muscle cells and muscular tissue is a matter requiring close inves-
tigation of cell-lineage, and whether the muscular tissue so formed
is or is not confined to that of the walls of blood-vessels. In

Fic. 17.—Sections or Two SraGes IN THE DEVELOPMENT OF HOLOTHURIA TUBULOSA TO
SHOW THE DEVELOPMENT OF MESENCHYME AT A PERIOD WHEN THE ARCHENTERIC
INVAGINATION IS ONLY COMMENCING.

mr, micropyle; fl, chorion; s.c, blastoccel; bl, cell-layer of the monoblastula; ep,
epiblast; hy, hypoblast; ae, archenteric invagination; and ms, mesenchyme. (After
Seleuka, from Balfour.)

Amphioxus we know that the somatic muscles are formed from
epithelial cells of the myoccel division of the cclom. Is this a
primitive or a secondary arrangement? If primitive, it is possible
that erstwhile epithelial cells of the ccelom migrate from the
pouch-wall in some other embryonic histories and form part of the
mass called mesenchyme. We cannot get further with the analysis
of mesenchyme until the first origin and subsequent history of
every constituent cell in a series of typical examples has been
determined. Meanwhile it is a distinct progress to cease from
speaking of coelom-forecast (Anlage) and mesenchyme as one
entity, viz. “‘mesoblast,” defying analysis. There is no constant
morphological factor to be recognised by the name ‘ mesoblast,’

has indeed been apparent for many years. Mesoblast ‘ding

32 THEORIES SINCE 1896

besides the parent-cells of the ccelomic epithelium, the skeleto-
trophic mesenchyme (mother-cells of connective tissue, blood,
and blood-vessels), traceable probably to endodermal parentage,
myoblastic mesenchyme probably derived from both primary layers
_ and neuroblasts derived almost certainly from both primary layers.
The parent-cells of the epiblastic nerve centres usually separate
together as a distinct mass at a later period of development from
the primary ectoderm, but there is abundant embryological proof
that so-called “ mesoblast ” may contain parent-cells of nerve tissue

as one of its constituents (e.g. in Cephalopoda). In some cases
too the single mother-cells of the nephridia take up their place :
the mesenchyme, migrating probably from ectoderm. There is still

a very large and very difficult field of research open to the student
of cellular embryology. The cell-lineage of mesenchyme and other
factors of mesoblast must be determined; it is not enough to.
have disentangled ccelom from this confused mass. When the’
cell-lineage of mesenchyme and its tissue products have been .
cleared up, we shall be able finally to put aside the hasty criticisms

and phantastic assertions of those who have grown impatient over

the slow and difficult task of Cellular Embryology.

(d) Third Stage of the Theory of the Cwlom from 1896 to the
present day.

:

A third stage in the progressive adjustment of the theory off
the ccelom is now in progress ; it has reference to the relation of —
the ccelom to renal excretory organs.

It had become abundantly clear in the early days of speculation —
concerning the ceelom that the reproductive cells both male and —
female are in all Ccelomocela epithelial cells of the coelomic
space. In the attempt to define the ccelom this fact was naa
use of, but it was also maintained by myself and others that the
communication of the ccelom with the exterior by at least one~
pair of renal excretory tubes was characteristic ; and the attempt
was made (and not unsuccessfully) to identify a given space as one ©
of ccelomie origin by the fact that it was placed in communication
with the exterior by means of such renal excretory tubes or sacs, —

Led by the principle that it is conducive to an ultimate dis-—
covery of the truth to assume uniformity of origin for similar
structures in diverse groups as a first hypothesis, rather than to—
assume a multiplicity of origins, I proposed (in 1877, Quart. Journ, —
Mier. Sci. vol. xvii. p. 429) the name “ nephridium” for the simple
renal excretory organ, and I took the so-called “ segmental organs ”
of the Earthworm as the type. I identified with this typical”
nephridium the excretory tubules of Platyhelmia and Rotifera,
the renal sacs of Mollusca, the peritoneal funnels and connected

ieee, —

tubules of Vertebrata, and later the renal tubes discovered by
Sanger and Balfour in Peripatus, and the various excretory and
genital ducts of other Arthropoda. The name “nephridia”
became very generally adopted by morphologists for all of these
structures.

It appears, however, that this generalisation was too sweeping,
as has been pointed out by Mr. E. 8. Goodrich, who has extended
to the Ccelomoccela in general the conclusions drawn by Prof. Ed.
Meyer from a study of the development of the Polychta (Meyer,
“Die abstammung der Anneliden,” Biolog. Centralblatt. vol. x.
1890). We have, in fact, hitherto included under the name “ neph-
ridium ” two quite distinet kinds of renal excretory tubules—the
one derived from single cells ultimately though not always actually
traceable to ectoderm, the other nothing more than a portion of
the ccelom itself communicating by a pore with the exterior. To
the first category belongs the type-nephridium—namely, that of
the Earthworm, and with it go similar tubules in other Oligocheta
and Polychzta, and the excretory systems of Platyhelmia and Roti-
fera. Hence, for these the name “ nephridium” must be retained.
To the second category belong the peritoneal funnels of many
Chetopoda, the funnel-like generative ducts of Oligocheta, the
whole series of so-called nephridia, modified and unmodified, in
Arthropoda, the renal sacs of Mollusca, and the peritoneal funnels

and connected tubules, whether of renal or gonoduct significance,

in the Vertebrata. The origin of these structures as parts of the
ccelom itself suggests the name of “ ccelomic funnels” for them.
The excretory activity of the wall of the ccelom and of these
specialised parts of it was, it must be supposed, acquired after the
first development of such conduits and pores to serve as exits for
the genital products from the celom. The name “ ccelomoduct”
is proposed now for the first time as the best general term for
these passages. Ccelomoducts are to be contrasted with nephridia ;
formerly they were confused with them. Ccelomoducts are parts
of the celomic wall itself; nephridia are ingrowths from a
superficial nephroblast. In the Mollusca we find embryonic,
evanescent renal organs which are nephridia (Pulmonata) ; these
disappear and are succeeded by permanent renal organs which are
ecelomoducts.

Nephridia do not always open into the celom, e.g. those of
Platyhelmia where the generative sacs are all that represents
celom. Celomoducts necessarily open into the ccelom at some
stage of their formation if not permanently, since they are part of
it. They do not necessarily open directly or indirectly to the
exterior, though they usually do so directly.

In the marine Chetopoda, according to the observations of
Meyer and Goodrich (Quart. Journ. Micr. Sci. 1899), there is often

é 3

C&LOM AND RENAL ORGANS 33

—

34 CQ@LOM AND RENAL ORGANS

a remarkable association of nephridium and eccelomoduct to form a
complex renal organ.

The theoretical conception that the renal tubules in the
animal series are of two distinct kinds, a more primitive and a
secondary, dates back to Gegenbaur. Continually the attempt
has been made to separate in a distinct category the nephridia
formed by a linear series of perforated drain-pipe cells from other
so-called nephridia with a lumen surrounded by many cells. It
cannot be said that the provisional doctrine of a single category
of renal organ in the entire series of Ccelomoccela, for which I am
responsible, had obtained very general assent amongst critical
embryologists, although the general use of my term “ nephridium .
for all sorts of renal tubes in all classes of animals might lead to
the assumption that such a community of origin was accepted.
The necessity for revising the doctrine of uniform origin of renal
tubes was pressed upon Goodrich by the careful determinations —
of the origin of these structures in some cases from ectoderm, in —
other cases from ccelom, by various embryologists in later years. ;
Thus Sedgwick says in his paper on the development of Peripatus —
in 1888: “It is important to notice that in Peripatus the —
nephridia are parts of the ccelom just as they are in Elasmo-
branchs. They are commonly spoken of in a manner which —
implies that they have but little to do with the ceelom beyond
opening into it. This way of speaking of them is calculated to
mislead. The nephridia are direct differentiations of part of the
celom” (Q. J. Mier. Sci. vol. xxviii. p. 391). On the other hand,
Vejdowsky has no less emphatically and conclusively shown that
the nephridia of certain Oligocheta are of ectodermic origin,
whilst Bergh and other observers trace them in many cases to-
peculiar superficially placed mother-cells lying in a so-called meso-
blast, each of which by division gives rise to a single row of
cells—a nephridium,

This difficulty is resolved by the recognition which we owe
to Goodrich of two categories of renal tubes: (a) The cclomie
ccelomoducets, which are primarily genital sacs and ducts, and second-
arily acquire renal functions; and ()) the nephridia, which are
primarily excretory tubules and only in the marine Chetopoda
acquire functions in connection with the ccelomoducts as genital
conduits (see Goodrich, Joc. cit.). .

Thus, then, we arrive at a further stage in the theory of the
celom. The true nephridia so long supposed to have a
morphological connection with it are separated from it altogether.
The organs which really belong to it and are, in fact, only parts
of it, whether appearing as renal sacs or genital conduits, are the
ceelomoducts. The ccelom is now, as a final result of observation
and speculation up to the present date, to be conceived of as

j NOMENCLATURE OF THE CQ:LOM 35

originally one or more pairs of detached or coalesced sacs originat-
ing ancestrally as pouches of the archenteron from which they
become shut off, having for their primary function the develop-

ment upon their walls of the male and female reproductive cells,
-and communicating with the exterior by simple or funnel-like or
tubular extensions of their own walls. They serve primarily as
the sites of the development of the genital products, but secondarily
may have a renal excretory function localised in a part of their
epithelial lining cells. Very generally they give rise to extensive
perivisceral and pericardial sacs, which remain continuous with
the original outwardly opening portions, or may be nipped off
from them and from each other.

(e) Nomenclature of the Parts and Derivatives of the Calom.

The various terms which are appropriate to, and useful in, the
discussion of the ccelom and its subdivisions require a brief special
statement. The terms may be best defined in a series of proposi-
tions which are more or less of the nature of a sketch of the evolu-
tion of the ccelom.

2

1. The primitive celom may be called a “ PROTOCHLOM
(Goodrich). It is probably multiple. Each protoccelom is in its
nature a GONOCEL (Goodrich), that is to say a ccelomic pouch,
the epithelial walls of which produce ova or sperm or both.

2. Probably at a very early period each protocceelom acquired
a “ C@:LOMOPORE” (Goodrich) or opening to the exterior.

3. The part of the protoccelom connected with the pore
frequently becomes narrow and funnel-like, and is then to be dis-
tinguished as a “cca:LomMopuUcT” (Lankester), whilst the rest of
the celom may persist as simple gonoccel or undergo further
developments.

4, Two (right and left) or more gonoccels may fuse and give
rise to an extended ccelomic cavity, the walls of which for the
greater part are not concerned in the production of gonad cells.
Such an extended cavity is generally known as a “perivisceral
Cavity” or “perivisceral ccelom.” It may be called the ‘“syn-
ceLom” (Lankester).

5. The syncceelom frequently develops renal-excretory functions
in the cells of its lining epithelium.

6. In segmented animals where pairs of ‘“ gonoceels” are
repeated in each segment, some may retain the function of pro-
ducing gonad-cells, whilst others become modified as renal-excretory
sacs. These latter are to be called ‘ UROCGLS” (Goodrich).

7. In some cases, ¢.g. some Mollusca, the gonoccel of one side
sof the body will retain its relation to the generative function,

>
ei

oe '

iF ns

36 NOMENCLATURE OF THE C&LOM

whilst its pair on the other side of the body becomes a pure uroccel;
various modifications of this kind are possible.

8. The ccelomoducts belonging to gonoccels may be called
“Gonopucts ” (Lankester), whilst the ccelomoducts connected with
urocels are to be termed “URoDUCTS.” Similarly the ccelomo-
pores may be called “GONOPORES ” and “ UROPORES.”

9. When the distinction between ccelomoduct and the rest of
the ccelom is marked by the development of a funnel-like mouth,
this funnel is termed a “C@LOMOSTOME” (Goodrich). Whilst
this is the general term applicable, it will in almost all cases be
actually either a “ gonostome,” i.e. a funnel leading from gonadie
celom into a gonaduct or a “urostome,” that is, a funnel leading
from uropéetic ccelom into a uroduct.

10. The duct-like portion of ccelom ending in ccelomopore may
be to a large extent replaced by ectodermal invagination compar-
able to the oral ectodermal invagination known as “stomodeeum,”
and to the anal ectodermal invagination known as “‘proctodzum.”
It is proposed (Goodrich) to term such ectodermal portions of
celomic ducts “C@LOMOD#A” (from 7d xofAwpa, the ccelom,
and déaiov, an adjectival form of 6éds). The ccelomodiea when
existent will, as a rule, be either “GoNoDmA” or “URODA&A,” and
it appears that their ectodermal epithelium may, in some cases,
acquire renal excretory functions.

11. Both gonoceels and urocels with or without specialised
gonaducts and uroducts may remain in open continuity with
the general ccelom (synccelom), or they may become closed off
from it. . ,
12. The synecelom (general ccelom) may become separated
into various chambers with or without obvious or microscopic
communication, infer se. It is undesirable to coin special terms
for all these chambers, but the possibilities comprise (1) a chamber
more @specially surrounding, or adjacent to, the main digestive
tract, the EPISPLANCHNIC CCELOM; (2) a PERICARDIAL C@&LOM; and
(3) paired EPINEPHRIC C&LOMS. In Vertebrates, the peritoneal
peripleural, and pericardial ccelomic sacs are well known and dis-
tinguished besides other minor divisions. These various divisions
of the ccelom may communicate or not with one another, or wit
gonoducts or uroducts, or both. Any or several of them may b
obliterated, or may be reduced to a canalicular form.

13. To be entirely distinguished from ccelomoducts, whethe
gonoceels or uroceels, are the NEPHRIDIA. Nephridia are probably
of ectodermic origin, and in any case arise independently fro
peculiar superficial nephroblasts or mother-cells. When devoid o
internal opening they are called PROTONEPHRIDIA (Hatschek).

14. Nephridia frequently acquire a funnel-like opening int
the celom. Such openings are called ‘ nephridiostomes.”

NOMENCLATURE OF THE C@&LOM 37

15. A nephridium may, as may a uroduct or gonoduct, acquire

‘a secondary element by ingrowth of ectoderm at the nephridiopore,

its original external opening. This secondary portion must be

termed “ NEPHRIDIODZUM” (Goodrich), the word being formed in
g

the same way as stomodzum and ccelomodeum.

16. Nephridia may become “grafted” in various degrees upon
uroducts and gonaducts in some animals (e.g. the Polychetous
Annelids), giving rise to organs of complex origin which cannot
be termed either “ nephridia ” or “‘ ccelomoducts,” since they have a
part of each category in their composition. The composite organ
thus formed may be termed a “‘ NEPHROMIXIUM” or ‘‘ NEPHROMIX,”
in reference to its hybrid composition.

The object of this introductory chapter is now completed.
That object has been the vindication of the ecelom as a morpho-
logical factor of primary importance in the animal series, and
the maintenance of the conclusion that the ccelom by its presence
justifies the separation of a higher grade of Enterozoa, the
Ceelomoccela, from a lower grade the Enteroceela, in which it is
not differentiated as a separate cavity.

-
7

CHAPTER IiIl

SPONGES !

PHYLUM PORIFERA.

CLASS I. CALCAREA (CALCISPONGIAE).

GRADE 1. HOMOCOELA.
4, 2. HETEROCOELA.

CLASS II. HEXACTINELLIDA (HYALOSPONGTAE).

Order 1. Lyssacina.
» 2. Dictyonina.

CLASS III. DEMOSPONGIAE.

GRADE 1. TETRAXONIDA.
Order 1. Carnosa.
» 2. Tetractinellida.

GRADE 2. MONAXONIDA.
Order 1. Halichondrina.
» 2. Hadromerina.

GRADE 3. KERATOSA.
Order 1. Dictyoceratina.
2. Dendroceratina.

bb] ——
GRADE 4. MYXOSPONGIDA.
(No Orders.)

I. INTRODUCTION.

THE Sponges or Porifera form a well-characterised group of

animals, very abundant in all seas, from the equator to the poles,

and flourishing at all depths, from the shore-line to the profoundest

abysses. One family (or sub-family), and, so far as is known, one

only—the Spongillinae—has established itself in fresh water, and is

represented by a great variety of genera and species in all parts of
1 By E. A. Minchin, M.A., Professor of Zoology, University College, London.

2 SPONGES |

the globe, wherever suitable conditions are to be found. The sponge
faunas of the present day are remarkable not only for the abundance
and the wide distribution of particular forms, but also for the

|
4

bewildering variety of species, genera, families, and orders; and —
these systematic categories are often defined, on the one hand, by

characters of apparently slight and trivial importance; and con-
nected, on the other hand, by numerous intermediate forms, to which
it is difficult to assign a definite position in the system. Hence,
while the classification of sponges frequently presents great difficulties,
at the same time there is perhaps no group which illustrates so
strikingly the theory of evolution and descent. Moreover, to judge
from the very large number and variety of fossil forms occurring in
strata of every horizon, sponges seem to have been at all times
equally abundant and widely spread, equally plastic and adaptable,
from the earliest geological ages to the present epoch. In contrast
with the extreme difficulty often encountered in defining and

separating the subdivisions of the Porifera, there is no group of —

organisms which, taken as a whole, is more easily recognised or
more sharply limited, both by reason of its peculiar features of
organisation and from the entire absence of forms in any way inter-
mediate between sponges and other forms of life. Hence it is not
surprising that the systematic position of sponges always has been,
and still is, much disputed. Even their animal nature was not
definitely determined till the middle of this century, and at the
present day there is much difference of opinion as to their true
affinities and proper position within the animal kingdom. These
are questions of which the consideration must be deferred until the
organisation and development have been discussed.

From the point of view of the student of animal structure and
functions sponges offer many points of interest, as representing
the simplest type of cell republic found in any animals above the
Protozoa. Their organs are, for the most part, single cells, less
specialised than in other forms, and therefore able to perform a
variety of functions, either simultaneously or at different times.
The absence, or at least the slight degree, of co-ordination between
their cells represents a primitive grade of organisation which other
Metazoa have passed beyond. Hence many problems of histology
and cellular physiology are here presented in their simplest form.

Il. Tot MorrpnHotocy AND Lirg-HISToRY OF SPONGES.
1. Ezternal Characters.

(a) Mode of Attachment—No sponge is known which, in the
adult state, is possessed ‘of locomotor organs, or has any power of
free movement. After passing through a transitory larval stage,

SPONGES

o>)

: during which it swims freely by means of cilia, the sponge passes its
whole subsequent existence fixed, except in a very few instances, to
some foreign object. The attachment may be direct, the base of the
sponge being in contact with the substratum, or indirect, that is to
say, by means of a root tuft of long spicules which serve to anchor it
as it were in the mud. The latter method is only found amongst
those forms, usually inhabitants of deep water, which live in mud
or ooze, and it is to be looked upon as a special adaptation to life
under such conditions.

Direct attachment is a rule without exception amongst Calcarea
and is the most usual method in all sponges, being universal amongst
forms which inhabit shallow waters and are subject to more or less
violent currents. The substratum to which the sponge is fixed may

_ be a rock or alga, or it may be some other animal such as a crab,
shell-fish, or tunicate. The adhesion is effected by the cells at the
point of attachment, which are glandular in nature, and in some cases
secrete a basal plate of spongin or some similar substance. The
portion of the sponge body which is in contact with the substratum
may be drawn out into a stalk or peduncle, often of considerable
length, by which the sponge is raised above its immediate surround-
ings (Figs. 8, 10, 11, 27, 37, and 38). In such forms the lower-
most portion of the stalk may be expanded into a foot or disc,
increasing the adhesive surface, or into root-like processes, as in the
fossil Ventriculites (Fig. 23).

Rooting tufts of spicules are specially characteristic of the
order Lyssacina of the Hexactinellids, where they are of very
frequent occurrence. They are also found in some Tetractinellids
(Fig. 24), but are very rare in Monaxonida and are unknown in
Keratosa and Calcarea.

The instances, very few in number, in which the adult sponge
is not fixed in any way, are to be found amongst a few species from
deep water. The remarkable form, Disyringa, for instance (Fig.
26), lies loosely on the sea-bottom, and a similar state of things is
met with in some other Tetractinellids from the deep sea. In such
cases the weight of the body, loaded as it is with siliceous spicules,
is probably sufficient to prevent the sponge from being passively
transported by the comparatively feeble currents to which it is
exposed.

(b) Form and Growth.—The typical sponge form is that of a

hollow vase or sac (Fig. 1), attached by its base to some object.
At its upper extremity is a conspicuous opening, termed the osculum,
and the wall is perforated by numerous minute apertures, the

_ pores. During life water enters by the pores, and passes, either
directly or after a more or less tortuous course along a system of
canals in the body wall, into the central space or “gastral cavity,

to emerge by the osculum.

4 SPONGES

The primitive vase-like form is retained in some instances
throughout life. In other cases it only occurs as a transitory
stage (which may even be suppressed) in the life-history, and
during subsequent growth it undergoes almost
every conceivable modification and complication
of form.

In the first place, any sponge, whether of simple
or complex form, may under certain conditions con-
tract itself and close up its pores and osculum. In
extreme cases even the gastral cavity becomes ob-
literated. Such changes of form are of course only
of temporary duration and are of no morphological
or classificatory value. Sooner or later the sponge
expands again and passes back into its normal con-
dition. Nevertheless, sponges in a state of contraction
have often been described as if they were the per-
manent form, and have even been separated from
the normal, expanded form as a distinct species,
genus, or family ; while the temporary obliteration of
the osculum or gastral cavity has been dignified by the
coinage of the terms lipostomy and lipogastry respec-
tively. Mistakes of this kind have been the cause of
great confusion in the literature, and it is well, there-
fore, to bear in mind that many sponges are ex-

Fig. 1. cessively contractile, while there are few that cannot

Olynthus of Clathrina close up their pores and oscula at will—that is to

2 ged pn edad (after SAY, aS a reaction to certain changes either in the
Haeckel). (The oscular environment or in the internal economy.

rim is not correctly re-
presented; the pores

should not be continued Apart from more or less rapid changes of
should stop at some dis- form resulting from contraction, we have to
ate consider a large series of form varieties which
are the result of growth, and therefore of greater permanence
and importance. It has been mentioned above that the region of
attachment may grow out into a stalk, and we have therefore to
distinguish, in the first place, between sessile and pedunculate forms.
It is convenient to commence the discussion of the variations in
body form by pointing out that almost any shape which a sponge
can assume may be further complicated by the growth of a peduncle.

At the outset the numerous form variations of sponges can be
classified into two distinct series, which start from a fundamental
morphological difference in the mode of growth. In the first place,
the primitive vase-like sponge, whether stalked or not, may retain
its single osculum and gastral cavity, but become modified in form
by unequal growth of the body wall. In the second place, the
growth may be such as to lead to the formation of new oscula, each
the vent of a separate gastral cavity. Anticipating here the theory

eee

~

4 ;

of sponge individuality which we intend to adopt (see below, p. 89),
the first-mentioned series may be termed modifications of the sponge
person, and the second, modifications of the sponge colony. Although
the two often merge into one another, we may consider them apart,
and commence with those cases where the sponge person remains

SPONGES 5

Fic. 4. Fia. 5.

Fic. 2.—Young specimens of Clathrina coriacea, Mont., x6. a, Olynthus; b, older stage,
with three diverticula commencing to form; ¢, still older stage, with diverticula anastomosing
to form the tubar system ; d, small colony with two oscula; osc, osculum ; div, diverticula.

Fic. 3.—Small colony of Leucosolenia Lieberkiihnii, O.S., x6. osc, osculum ; div, diverticula.
Fic. 4.—Arborescent colony of Leucosolenia complicata, Mont., x6.

Fie. 5.—Creeping colony of Leucosolenia variabilis, H., with numerous erect, and for the
most part simple, oscular tubes, arising from a basal creeping stolon, x6.

single—that is to say, where the sponge retains a single osculum and
gastral cavity.

The wall of a primitive vase-like sponge may increase during

growth either in superficial extent or in thickness, or in both ways at

' once. We may consider first the results of an increase in the

6 SPONGES

surface of the body wall. In the first place, such increase may take
place more or less evenly and regularly in all parts, but more
rapidly in one direction than in another; then the sponge person
becomes an elongated cylinder or tube if the growth be chiefly

Fic. 6.
Young specimen of Clathrina reticulum, O.S., with one osculum, x6.

vertical, or assumes the form of a cup or saucer if the growth be
chiefly horizontal. In the second place, the growth may be uneven
or irregular, being more rapid in one part of the sponge body than
in another, or taking place chiefly in certain limited regions. In

ee ee ee eee

|

———— y/

i a)

NN MN
Fia. 7.

Clathrina clathrus, O.8., natural size, semi-diagrammatic combined figure. On the left the
sponge is represented in the state of extreme expansion, passing gradually into that of extreme
contraction on the right. ose, osculum ; el.osc, closed osculum ; contr.osc, elevated ‘‘ conules”
in the contracted portion representing oscula contracted; sph, sphincter of osculum; div,

diverticula ; osc.div, vertically directed diverticula from which new oscula arise.
such cases either the body wall must be thrown into folds, or the
primitive form of a vase or sac will be distorted or modified in

various ways.

Instances of both tubular and cup-shaped sponge individuals are ©
common amongst the Hexactinellids. The first type is well seen in such
forms as Regadrella (Fig. 18) and Euplectella (Fig. 15); the second in such —
a form as Asconema (Fig. 17). The tubular forms may assume an erect

4

cylindrical form (Euplectella suberea), or may be more or less curved like
a cornucopia (£. aspergillum).: A remarkable instance of horizontal growth
of the body wall is seen in Caulophacus (Fig. 20, C), where the wall of the
gastral cavity is turned outwards and downwards, and the sponge being at
the same time stalked, a form like a mushroom results, in which the upper
convex surface of the disc represents morphologically the inner surface of
the body, and the rim of the dise is the down-turned margin of the
osculum, An approach to this condition is seen in the fossil Ventriculites,
Some specimens have the body shaped like a paper basket, while others
have the margin very much expanded and everted (Fig. 23). Mantell
(1822) makes the suggestion that the differences in different specimens of
Ventriculites may be due to contractility.

A good example, on the other hand, of the effect of rapid local growth
is seen in the Hexactinellid sponge Hwryplegma (Fig. 20, A). Here the
primitive vase-like organism grows with great rapidity on one side, and
scarcely at all on the other. The result is an ear-like or shell-like form,
in which the concave side represents the gastral cavity, and the whole free
edge the margin of the osculum (m.osc). This mode of growth is carried to
its extreme in Poliopogon (Fig. 20, B), where the sponge has become simply
a curved plate, of which the upper edge represents the oscular margin
(m.osc), the concave side the gastral cavity.

SPONGES -

If the portions of the body wall which grow more rapidly are
distributed, so to speak, in patches, the result will be the formation
of diverticula or folds. The best instances of this are seen in the
calcareous sponges, all of which begin their existence as a vase-like
organism of very primitive structure, termed the Olynthus (Figs. 1
and 2, a). Hence the Calcarea are specially suited for tracing out
the processes of growth by which the often complicated body form
is attained.

In the most primitive Calcarea, the Ascons, the Olynthus grows
in height, becoming tubular, while at various points on the surface
hollow diverticula are thrown out on every side. The diverticula
increase rapidly in length, and become branched, and by coalescence
and anastomosis of the branches there arises a network of tubes,
which surround, and open into, the central oscular tube, represent-
ing the original Olynthus. The continuous cavity which extends
through the whole tubar system is, of course, the now greatly

‘ramified and subdivided gastral cavity.

Two types of body form can be distinguished in Ascons as the result
of simple variations in the mode of growth above described. In the
family Olathrinidae the vertical growth of the Olynthus is comparatively
slow, the horizontal growth of the diverticula comparatively rapid. In
the family Leucosoleniidae, on the contrary, the Olynthus grows rapidly
in height, while the diverticula, though more numerous, remain relatively
small. Hence the typical Ascon person is, in the genus Clathrina, a
dense network of ramifying tubes opening by a short and often in-

” significant oscular tube (Figs. 2, 6,7, 8 ; ef. Fig. 65, A), and in the genus

8 SPONGES

Leucosolenia, a large and erect oscular tube giving numerous diverticula
of comparatively small calibre, which increase in length towards the base
of the tube, where they tend to branch and anastomose (Figs. 3, 4, 5;
ef. Fig. 65, B).

A body form very similar to that of Ascons, and the result of a
similar mode of growth, is also of common occurrence in the order
Dictyonina amongst Hexactinellids (Figs. 21, 22). The primitive
vasiform sponge person becomes first tubular and then branched,
and by anastomosis of the branches a network of tubes results.

In the higher calcareous sponges, the order Heterocoela, we find
a mode of growth which, though essentially similar to that found
amongst Ascons, leads to a body form considerably different, and
in most cases much simpler. As typical may be taken the genus

es by
it Fia. 10.
oo
A, Sycon raphanus, O.S. (after Schmidt),
x 5. B, Sycon humboldtii, Risso (=Dun-
Fic. 8. stervillia corcyrensis, O.S.), (after Schmidt),
9 =
Clathrina lacunosa, Fic. 9. x 2}.
Johnst., colony with : ve
two oscula, sed Sycon bia Fabr.,

Sycon, where the Olynthus sends out numerous breast-shaped
or thimble-shaped diverticula, more or less regularly disposed on
every side. New outgrowths continually appear just below the
oscular margin and continue to increase in size, but unlike what
has been described for Ascons, the diverticula in Sycons have a
limited growth. The size attained by the diverticula is greatest at
the sides and towards the base of the sponge. As a result of this
mode of growth the sponge assumes a strobiloid form, which in some
primitive types is more or less retained throughout life. In
most Sycons, however, the diverticula become united by secondary
growths at their apices, and are thus rendered indistinguishable in
an external view of the sponge. Hence the effect produced is
simply that of a great thickening of the body wall. The Sycons
furnish, in fact, a clear instance of the body wall of the primitive

i ee

a

sponge undergoing an apparent thickening which is in reality due to
the formation of folds and their subsequent coalescence, and it will
be seen in discussing the canal system that all thickening of the wall
of the primitive vase-like sponge organism is to be interpreted morpho-
logically in a similar manner. Since in Sycons and Heterocoela
generally the body usually grows more or less evenly in all parts
at the same time that diverticula are being formed all round, the
primitive form of a vase is more often perfectly preserved in these
sponges than in any others, though subject to variations of form of
subsidiary importance, such as the addition of a stalk (Fig. 10)
which in the genus Ute reaches a great length. A remarkable
departure from the primitive

form is seen, however, in €.

Grantia labyrinthica (Fig. 11).
The young sponge of this
species has the form of a

SPONGES 9

Fia. 11. - 4
Grantia labyrinthica, Crtr. Three stages aCe tae
of growth. (After Dendy.) Leucandra aspera H., natural size.

stalked cup, with a thick body wall, formed as above described,
by folding and coalescence. Further growth of the body wall
causes it to be thrown into numerous folds, the edges of which
represent the greatly extended oscular margin. Another Hetero-
coele sponge of aberrant form, requiring no explanation, is Lilhardia
Schulzei (Fig. 13).

It is evident from the instances that have been adduced, that
the changes in the form of the sponge person which result simply
from an uneven or local expansion of the surface of the body wall,
are numerous and often complicated, but may, however, result in a
simple thickening of the body, and a consequent retention of, and
reversion to, the primitive form.

As a result of a disproportionate increase in the thickness of

10 SPONGES

the body wall the primitive vase-like sponge person may assume
a more massive form, and in the simplest cases becomes barrel-
shaped (Fig. 16) or globular (Fig. 30), according to the degree of

Fic. 13.
(After Poléjaeff, Challenger Reports.) Natural size.

Eilhardia Schulzei, Pol.

thickening. If the growth predominates at the base of the sponge
it acquires the shape of a shallow cone or volcano, the crater being
represented by the osculum, and in such forms the vertical height

Fic. 14.
mans, Mant. (After Zittel.) B, Petrostroma Schulzei, Déd.
(After Déderlein.)

may be very small as compared with the horizontal extent, until in
extreme cases the sponge becomes a mere crust, spread over the
surface to which it is attached, and rising slightly in the region of

the osculum. On the other hand, the sponge may become sub-

SPONGES

"
Ath ae
= ee
eae tad
NA
Sian
N iD
RIN
Y)
ee,
y
¥

hs

reco
2 PONE
ERE SS
espa:
- 2) =
iting
SA
Ty ag:
-

Euplectella aspergillum, Owen. (After Wyville Thompson.)
4

SPONGES

lla

velata, W. Th.

(After Wyville Thompson.) Natural size.

SPONGES 13

cylindrical, and narrower at the base than at the summit, as in the
ease of Zentorium (Fig. 31), and any form of massive sponge may
be further complicated by the formation of lobes and irregularities
on the surface, or in other ways. In the fossil Siphonia the
massive sponge has developed a stalk, and has the form somewhat
of a rose-bud, at the apex of which the relatively small and reduced
gastral cavity opens by the osculum (Fig. 27, 4 and B).

Two remarkable sponge forms are seen in the genera 77i-
brachion and Disyringa amongst Tetractinellids. Both of them are

Fic. 17.
Asconema setubalense, Kent. (After Wyville Thompson.) }.

to be regarded as massive forms in which the more or less globular
body is not fixed, but lies loosely in the mud at the bottom of the
sea, and which have developed peculiarities of structure correlated
with their mode of life. Thus 7ribrachion (Fig. 25) has developed
an oscular tube of great length, while in Disyringa (Fig. 26) not
only is the exhalant aperture prolonged in like manner into an
elongated tube, but also an inhalant tube is developed, terminating
in a single aperture by which is taken in all the water which
enters the canal system. The cavity of the inhalant tube forms a
sort of atrial chamber, as it were, in which all the pores are collected,
and no pores are found on the surface of the body. Disyringa is

SPONGES

14

19.

Fic.

oF S w¢

cSEPE SE
7 '>5 236
oe el =
s Son 4
SoBe w &
= ®a=2
Ss ase
Salee 4
SRSs 2
Ss 2£se20o
ak |
Reese.
a

18,

Fia.

(After Agassiz.) 3.

O.8.

phoenia

Re gadrella

=
»
=

2)

at =

ma Ins *~
=.

=

<
*
cs

Spee a
Wey

ee
nore THO fis tip ae

sage:

ee HT

ré eee =

ghee

*
sy

tl
Ca at iy
.
. *.
ao
hike 71

se
i:

A, Euryplegna cwuwriculare, F.E.S.
F.E.S. All three after Schulze.

SPONGES 15

Fic. 20.

B, Poliopogon amadou, W. Th. C, Caulophacus elegans,
A, reduced 4; B, 4; C, natural size.

unique amongst sponges in possessing an inhalant tube of this kind,
doubtless advantageous to the sponge, living as it does partially
buried in the soft ooze.

Having considered the chief types of form which the sponge

Fic. 21.

Farrea facunda, O.S. (After Agassiz.) 4.

16 SPONGES

individual may acquire as the result of its particular mode of ©
growth, it remains to discuss the forms assumed as the result of
multiplication of individuals which remain united. Since the

Fia. 22.

Aphrocallistes Bocagei, Wright. (After Agassiz.) x 3.
sponge colony consists of an aggregation of sponge individuals, pro-

duced one from another by a process of budding, its form will -
depend largely in the first instance on the type of sponge persons

Fia. 23.
Ventriculites, imagined reconstruction. 1, root-like processes of attachment; ose, osculum. 7
A piece of the margin is represented broken away to show the plications which form the in- —
current and excurrent canals. d

of which it is composed. The other factors which influence the
form of the colony are, first, the way in which the individuals are
united together—that is to say, the manner in which they are budded —

SPONGES 17

off from one another ; and secondly, the degree to which the indivi-

Fic. 24.
Thenea muricata, Bwk., natural
size. r.t, root tuft; p, symbiotic
polyps (Palythoa).

Fig. 25.
Tribrachion Schmidtii, Weltner

(after Sollas). sp.b, sponge body ;
e.t, exhalant tube. ssa

duals produced in this way become
distinct from one another, or remain
fused together.

Instances of the way in which
the mode of budding and the union
of the persons influence the form

OSC.

é.l---~--

Fic. 26.

Disyringa dissimilis, Ridley (after Sollas). A,
the whole sponge reconstructed from fragments.
i.o, incurrent aperture; i.t, ineurrent tube; sp.b,
sponge body; e.t, exhalant tube; osc, osculum. B,
diagrammatic vertical (longitudinal) section of the
sponge. a,b, c, transverse sections at three different
points ; a, showing the four divisions of the excur-
rent tube; and b, the four divisions of the incurrent
tube, which at ¢ is undivided.

of the colony as a whole are well seen in Ascons, and especi-
ally in the genus Leucosolenia, where the individuals can be easily

distinguished. In the simplest cases the new oscular tubes arise
from the tubar system by the side of the parent individual, and the

e> SPONGES

Fig. 27.

Siphonia tulipa, auct. (after Zittel). A, a vertical section of the body, natural size, showing
the small gastral cavity, the radially directed incnrrent canals, and the concentrically disposed
excurrent canals. B, the entire sponge, half natural size.

colony assumes a compact or bushy form (Fig. 3), which may take
on a spreading or an arborescent growth by variations in the mode

A, Setidiwm obtectum, O.8., 3. LB, Colinella inseripta, O.S., 3. (Both after Agassiz.)

of budding. In the spreading forms (Fig. 5) the diverticula at the
base of the sponge person come into contact with the substratum
and grow to a great length, forming a stolon-like basal network,

SPONGES 19

ramifying only in one plane, from which arise erect diverticula at
intervals which acquire oscula at their extremities, and thus assume
the characters of new individuals. In the arborescent forms, on
the other hand (Fig. 4), the erect oscular tube sends out numerous

Fic. 29.
Vetulina stalactites, O.S. (After Agassiz). 3.
diverticula along its whole length, which form new oscula at their
extremities when still quite short, and the daughter individuals
which are thus formed repeat the same process, throwing out
diverticula rapidly on every side. In this way arises an arborescent

Fic. 30.

A, Tethya lyncurium, L., natural size. At the summit is seen the partially retracted
osculum. J, section across Tuberella sp., showing the thick cortex and the radial arrangement
of the body skeleton.

Ascon colony which creeps over the seaweeds like a climbing plant,
attaching itself at intervals by direct contact. Among the Hetero-
coela, also, erect arborescent colonies are not uncommon, and in
Leucandra aspera (Fig. 12) rapid growth and budding may lead to

SPONGES

a form resembling a cock’s-comb. In the British species Lewe
wives, a spreading colony is formed, composed of numerous fla’
voleano-like individuals.

In the cases where the persons of the colony are not dis
from one another, the colony as a whole may have a form
differing from, or even identical with, that of the sponge individu
and in extreme cases the colony can only be distinguished from the
individual by its larger size and greater number of oscula. Instances.
of this are well seen in the genus Clethring among Ascons, where
the full-grown colony forms a spreading mass of tubes. Typically
the individuals are indicated in these forms by cone-like elevations
of the tubar system, each surmounted by an osculum (Fig. 7, Ch
elathrus). Tn some species of the genus, however, the sponge assumes __
a very compact form, like a cushion when sessile (Fig. 6, Ch

Fre. 32,

Tentoriem cmiseterittes, QS. On
the left-hand, an older specimen with
wumeroaws oseula > on the right, a yours
Specimen with ome osculum; eacf,

gsoular tubes ; 4, dase of attachment, OpAlitespongia seriaga, Bwk. ose, oseula.

reticulum), or more or less globular when stalked (Fig. 8, Cl. Jecunesa),
and then the number of oscula alone indicates the number of
individuals. In other cases, again, the tubes may ramify in one
plane, forming an incrusting colony spread over stones or seaweeds,
from which oscular tubes arise at intervals.

Instances of sponge colonies in which the form of the colony is more
or less identical with that of the individual are very common also
amongst siliceous and horny sponges. The best examples are seen im
massive forms, such as Euspeagia or Tentforiwm (Figs. 39 and 31), where t
separate individuals are quite indistinguishable from one another, and are
only indicated by the oscula. In such cases the composite individuality of
the sponge can scarcely be recognised; it becomes simply a compact
growth in which the repetition of a number of similar and complete
physiological systems alone marks the primitive individuals,

Most of the sponges in which the loss of individuality is most

SPONGES

ked are inhabitants of shallow water; or, if not, they are
forms whose nearest allies are to be found along the shore, and
whose ancestors have probably migrated into deeper water in com-
paratively recent times. In other words, the “impersonal” con-
dition, as it may be termed, seems to have been correlated at its
first origin with life in a habitat where the sponge has to contend
with, and to adapt itself to, the action of stresses and strains which
are always very variable and often very severe, and where the

| Fic. 33. : Pia. 94.
Spongilla lacustris, auct. (after Chilina oculota, Pall, half-natura) size.
: Weltner). 4 osc, oscula ; st, stalk.

form of the sponge becomes of the greatest importance in the
struggle for existence. Hence the sponge colony as a whole takes
on some characteristic mode of growth which may vary greatly
from species to species, or even in different specimens of the same
species. In this way a great number of different shapes and forms
arise which are often extremely irregular and amorphous, but which
can usually be classed under one of a series of typical forms.
As the starting-point we may conveniently take a small com-
"pact sponge with numerous oscula—that is to say, a colony in which

. .
”

:
3

to
ty

SPONGES

the persons are indistinguishable except by the exhalant vents of
the canal system.
A compact sponge of this kind, if it grows more or less equally

in all directions, becomes simply massive (Fig. 39). It may, how-

ever, grow very greatly in a horizontal direction, and increase very
little, or not at all in height; this gives a flat incrusting form, in
which the oscula may be prominent as elevated cones or tubes, or
may be quite inconspicuous (Fig. 32). On the other hand, the

Fic. 35. Fic. 36.
Phakellia ventilabrum, Johnst. A, flabellate

specimen, B, cup-shaped specimen. Phakellia tenax (after Agassiz). 4.

young sponge may grow very rapidly in height, and in this way a
large series of forms arises. In the first place, a sponge which
grows vertically may become greatly branched and assume a
dendritic form (Fig. 34). The numerous oscula are found scattered
along the branches, which in their turn may be more or less circular
in transverse section, or very flattened. In the second place, rapid
growth of the sponge in a vertical direction in height may be com-
bined with a horizontal growth which preponderates in, or is
restricted to, a particular vertical plane ; the result is a fan-shaped
or flabellate form (Fig. 35, 4),a type which may undergo subsequent
modifications of great importance.

Zl

SPONGES 23

In flabellate forms the oscula are usually, if not always, found
on one side of the sponge, the inhalant orifices on the other side.
Flabellate sponges have a great tendency to become folded until
the edges come into contact and undergo concrescence. This can
be well seen in such a form as Phakellia ventilabrum, where some
specimens are simply fan-shaped, and others are folded into the
form of a funnel or cup, in which the surface which bears the oscula
is internal (Fig. 35, 6). In this way a large series of sponge forms
arises which, according to the relative dimensions of different
regions, may be funnel-shaped, cup-shaped, or tubular. In the
interior are found the true oscula, and on the exterior the inhalant
apertures. The sponge colony in these cases exactly resembles the
primitive vasiform sponge individual, or some of its numerous
modifications, and at first sight the terminal aperture might be
taken for a true osculum, the central space for the gastral cavity,
and the exhalant vents-in the interior for the excurrent openings
of the canal system. Hence the cavity in these secondarily cup-
shaped or tubular forms has been termed a pseudogaster, and the
terminal aperture a pseudosculum. In many cases, however, it is
impossible to determine either by simple inspection or by dissection
whether a cup-shaped or tubular sponge represents a single in-
dividual with a true osculum, or a colony with a pseudosculum.
Similarly, a flabellate sponge may represent a colony composed of
numerous individuals, or it may be, as we have seen in the case of
' Euryplegma, a single individual, modified by its peculiar mode of
growth. A knowledge of the development can alone decide which
view is the correct one in any given instance.

Another modification of the flabellate type is seen in Phakellia
tenaz (Fig. 36) in which the fan has become fenestrated, resulting in
a Gorgonia-like form.

Many deep-sea sponges, especially those of the order Monax-
onida, are to be regarded as having migrated downwards from the
shore-line in comparatively recent times, and in such forms the
influence of life in still water is seen in a great regularity of growth,
resulting in the development of a secondary symmetry. A good
instance of this is furnished by the remarkable form Lsperiopsis
Challengeri (Fig. 37). Both the genus and the family (Desmacido-
nidae, R. and D. = Poeciloscleridae, Tops. pars) to which this sponge
belongs comprise some of the commonest and most characteristic
sponges of the littoral fauna, and its nearest allies exhibit the
variable and often irregular form which in sponges is associated
with life in shallow water. Like its allies, the species under con-
sideration is a colony in which the individuals are indistinguish-
able, but a more tranquil and uniform environment has favoured
a regular and symmetrical growth which is clearly not of a primi-

_tive type.

24 SPONGES

(c) Colour.—The colours of sponges are very varied, and often
very bright, especially in the case of species inhabiting the shore-
line, rendering them very conspicuous objects, and contributing
largely to the display of colours in the submarine scenery of caves

Fig. 88.

Stylocordyla stipitata, Crtr.
(after Agassiz). 4.

Fic, 87. Fra. 39.

Esperiopsis challengeri, R. (after
Ridley). 4. Euspongia oficinalis, L. (after Schulze). 4.
and sheltered spots along the coast. Many sponges, however, have
no special colouring-matter, and then are simply white or gray, the
prevailing tint amongst Calearea. The littoral species of Demo-
spongiae, on the other hand, are usually brightly coloured, especially
in the Monaxonida and Keratosa, various shades of yellow, orange.
red, or lilac being the prevailing tints, but blue is not uncommon,

z

Green is a rare colour amongst marine sponges, but is the usual
tint of the fresh-water Spongillinae, where, however, it is due to
chlorophyll. When the chlorophyll is not developed, fresh-water
sponges are usually brownish. In marine forms chlorophyll is
seldom, if ever, found as a pigment, and the nearest approach to
the bright green of Spongilla is a dull olive-green of not infrequent
occurrence. }

Although Calcarea are usually colourless, some remarkable and
instructive instances to the contrary are found amongst them, especially
in certain species of Clathrina. Thus Cl. coriacea, common along the
shores of the British Channel, has a wide range of colour variations,
different specimens being white, yellow, orange, red, or lilac. The
particular colour which a colony assumes does not seem to bear any fixed

SPONGES 25

- ; Oscarella lobularis, O.S. (after Schulze).
Fic. 40. Natural size.

Aplysina aérophoba, Ndo. (after
, Schulze). 4.

relation to other characters of its form or structure, nor is it as a rule cor-
related with its habitat, since specimens of the most diverse hues may be
found in the closest proximity, growing even on the same stone. On the
other hand, the specimens of this species living below the ordinary tide-
marks in certain localities are constantly of a pale lemon-yellow colour,
and this tint has become fixed as the constant colour of an allied species,
Cl. clathrus, of the Mediterranean, while Cl. primordialis, another
Mediterranean species, shows the same variability as Cl. coriacea. The
larvae of each colour variety have the same tint as their parent, but it is
not certain how far the colour is constant during the life-history of a
given individual. It is not improbable that it may change according to
the circumstances of its metabolism or from other causes at present unknown,
since the peculiar cell-granules, which are the seat of the colour, are very
variable in quantity and may be almost entirely wanting (temporarily ?)
in some specimens.

The colouring-matter of sponges is contained in cells of the
dermal layer, especially in the epithelium asarule. Special pigment
cells are not found. The colouring-matter is usually very fugitive

26 SPONGES

and difficult to preserve, being easily dissolved out. In Calcarea
the cells of the dermal layer, and more especially the flat epithelium
and the porocytes, contain numerous opaque granules, which are
the seat of the pigment in coloured forms. When the sponge is
placed in alcohol, the colouring-matter dissolves rapidly out of the
granules, making the specimen a dull white or brownish colour, and
in fact reducing it to the condition of the forms without pigment.
In many Demospongiae, on the other hand, the pigment is more
resistant. Aplysina aerophoba is remarkable for possessing a pale
yellow pigment which becomes blue, and finally black, on exposure
to air, apparently by oxidation (Krukenberg). In alcohol it turns
reddish-brown.

(d) Consistence, ete—Different sponges yield very different sensations
to the touch, according to the degree to which the skeleton is developed,
the nature of the materials composing it, or the texture of the surface of
the skin. The Myxospongida are soft, slimy, and easily squashed. The
more primitive Ascons, for example Clathrina clathrus (Fig. 7), are
excessively delicate when fully expanded, and collapse by their own weight
if lifted out of the water, but acquire considerable firmness and rigidity as
the result of contraction. Many calcareous and siliceous sponges, on the
other hand, have the surface roughened by projecting spicules, while the
body may be brittle or friable and easily broken, or it may be very tough
and even of almost stony hardness. In the Keratosa, the body is yielding
and slimy to the feel, but, at the same time, excessively tenacious, very
difficult to tear or pull apart, This feature is due to the tough elastic
spongin fibres composing the skeleton, and is found also in Monaxonida
according to the degree to which spongin is developed as a constituent of
their supporting framework.

Many sponges have, when living healthily, a strong and disagreeable
odour, rather resembling garlic. This characteristic is very pronounced
in the common fresh-water sponge.

2. Anatomy and Histology.

The Olynthus.

The Organisation of Sponges in General.
(a) Canal System.
(b) Skeletal System.
(c) Histology.

The Olynthus.—The simplest known type of sponge, in structure,
as well as in form, occurs, as has been said, as a transitory stage,
the so-called Olynthus, in the life-history of all calcareous sponges.
In the Olynthus the problems of sponge anatomy and physiology are
reduced to their lowest terms, and all sponges may be regarded
ideally as derived from it, even though the Olynthus stage may not
actually appear in their ontogeny.

‘1 The organism in question received its name from Haeckel, who was under the
impression that it represented an adult generic type.

a

The body form of the Olynthus is typically that of a hollow
vase, as described above, though it may vary a good deal in its con-
figuration. Fig. 2, a, shows the Olynthus of Clathrina coriacea ; Fig. 1
represents somewhat diagrammatically, and more highly magnified,
that of an allied species, Cl. primordialis ; and Fig. 60, h, that of Sycon
raphanus. As a type for description may be taken that of a simple
Ascon (Clathrina).

The wall of the Olynthus (Fig. 1) is perforated by numerous pores,
and at the summit is situated the large exhalant aperture or osculum,
often defended by a contractile sphincter or sievemembrane. The
body wall is composed of two layers of tissue, which may be termed
the dermal and gastral layers respectively. The dermal layer is
the more externally situated and makes up the greater part of the
sponge. The gastral layer lines the interior, but does not reach
quite to the extreme margin of the osculum, the opening of which
is surrounded by a rim or collar of variable length, made up of the
dermal layer alone (Fig. 42, 4 and D, p.c.ep). Both layers are inter-
rupted by the pores, which perforate the wall everywhere except at
the base of attachment and in the oscular rim.

The gastral layer is very simple in its composition, being made
up of a single stratum of columnar epithelium, the cells of which
are all of one peculiar type (Fig. 42, 4 and D, ch.c). Each cell
bears at its upper free extremity a single vibratile flagellum (/2),
which springs from the centre of an area enclosed by a delicate cup
or collar of protoplasm (c). On account of the latter peculiarity
these cells have been termed collar cells or choanocytes, and are very
characteristic of sponges. In all sponges that have been studied
the gastral layer is composed of these cells and of these alone ; on
the other hand, similar cells are not known to occur in any
Metazoa, but each collar cell is strikingly similar to a protozoon
individual of the class Choanoflagellata.

The dermal layer consists mainly of a gelatinous ground sub-
stance, which is covered on all its exposed surfaces—that is to say,
on the exterior of the body wall and in the oscular rim—by a
flattened epithelium (d.ep), and contains the skeletal elements and
their secreting cells and the pore cells. The flattened epithelium
is the contractile layer of the sponge, and where the body wall is
in contact with the substratum at the points of attachment, the
epithelium is of a glandular nature. The skeleton consists, in Cal-
carea, of spicules of calcite (sp) secreted within cells termed sclero-
blasts (sp.c). Each pore (/) is a perforation through a single cell,
the pore cell or porocyte (/.c), which stretches from the external
flat epithelium to the internal layer of collar cells, and places the
gastral cavity in communication with the exterior by means of an
intracellular duct or canal. The pore canal opens towards the
interior by a wide aperture (Fig. 42, 4 and D, g.a) between the

5

SPONGES 27

F. Veen > =

Fr. 42

Histology of the body wall of Cluthrize crises, Mont. A, body wall seen from the inside
im the region of the oscular rim. B, portion af 4, showing the sume three pores (p!, p> and
another), bat with the collar cells removed, to show the underlying parenchyma. (C, same
portion of the body wall, with the pores ». ye, but seem from the outside, to show the G8
epithelium. D, longitedizal section of the body wall, im the region of the oscular rim, folly)
expanded. E. section of the body wall, slightly contracted. F, section of the body wall, very
contracted. 4. R and Cx T30; DE, F, xX SQA = emc, amoebocytes ; epic, apical formative)
cell: bfc, basal formative cell; ¢ collars of (ch.c) choamoeytes ; de, dermal aperture of pore5)
dep, dermal epithelium ; #. fiagella; g.«, gastral aperture of pore; p’, p4, pores; pc, POR:
cytes ; pcep, porocytic epithelium ; sp, spicule ; sp.c, spicule ceil or scleroblast.

SPONGES 29

cells of the gastral epithelium, and towards the exterior by a fine
opening in a delicate, protoplasmic diaphragm situated on a level
with the dermal epithelium (Fig. 42, 4, b, C, and D, d.a).

Both scleroblasts and pore cells are derived directly from the dermal
epithelium which in the embryo at first constitutes the whole of the
dermal layer. Cells of the epithelium migrate inwards to become sclero-
blasts ; other epithelial cells, distinguished by their larger size and
numerous granules, become porocytes in two different ways in different
regions. In the oscular rim the epithelium lining the interior becomes
modified as it approaches the gastral layer, until its cells have the
characters of porocytes (Fig. 42, A, D, pc.ep). As the collared epithelium
grows upwards by proliferation of its cells during the growth of the
sponge, the lowermost epithelial cells of the oscular rim become sur-
rounded by collar cells which pass between them and isolate them from
one another. Each cell of the lining epithelium of the oscular rim when
thus cut off from its fellows becomes a pore cell. In other regions of the
body wall the ranks of the porocytes may be recruited by the direct im-
migration of large granular cells of the dermal epithelium, and their
subsequent perforation to form new pores.

In addition to the collared cells of the gastral layer and the
various cell elements of the dermal layer, the body wall contains
numerous wandering cells or amoebocytes (Fig. 42, Bb, D, E, F, am.c),
which occur everywhere amongst the cells and tissues. Though
lodged principally in the dermal layer, they are not to be regarded
as belonging to it, but as constituting a distinct class of cells in
themselves. They are concerned probably with the functions of
nutrition and excretion, and from them arise the genital products.

The above description of the Olynthus applies to it in the
normal expanded condition, when the sponge is feeding actively,
with pores and oscula widely open. The cells of the flattened
dermal epithelium, however, as well as the porocytes, are excessively
contractile, and by their contraction bring about important modi-
fications in the appearance of the sponge as a whole, as well as in
the disposition of its cells and tissues. Each porocyte can close up
its apertures and obliterate its lumen by its own contraction, and
in this condition the porocyte has the appearance simply of a com-
pact, granular, amoeboid cell. The contraction of the dermal
epithelium brings about the closure of the osculum and the con-
traction of the sponge as a whole. The closure of the osculum is
effected more especially by the large granular epithelial cells,
destined to become porocytes, which line the oscular rim, and from
these cells a special contractile apparatus, such as a ring-like
sphincter or a contractile sieve-membrane, is often formed in this
region. The flat epithelium covering the exterior, on the other
hand, is responsible for the general contraction of the whole body, and
by its action brings about a reduction in the internal gastral cavity,

30 SPONGES

proceeding pari passu with a thickening of the body wall, and
resulting in a considerable diminution in the size of the sponge as
a whole. When the contraction is carried to its extreme, the
gastral cavity disappears altogether and the interior of the sponge
is filled by a solid mass of cells.

During the contraction of the sponge, the arrangement of its cell
elements undergoes great changes, which are very important for interpret-
ing the early stages of the embryonic development. The collar cells
become first laterally compressed and very columnar (Fig. 42, 2), and
finally are forced over one another into several layers (Fig. 42, F, che).
During these changes the collar shortens, and is finally completely
retracted. The spicules are also forced one over the other to form several
layers.. The porocytes, which at first were lodged in the body wall below
ternal to) the collar cells, pass between the latter (Fig. 42, 2), and finally
take up a position over (internal to) the collar cells (Fig. 42, F’), forming
an epithelium lining the now greatly reduced gastral cavity. When the
contraction reaches the stage in which the gastral cavity is completely
obliterated, the collar cells and porocytes fill the gastral cavity as a
compact mass of cells, the porocytes being aggregated towards the centre,
or rather the axis, of the sponge. Lastly, the cells of the dermal
epithelium, the active agents in bringing about the contraction, them-
selves undergo a remarkable change of form. As the cell contracts, the
nucleus and the central protoplasm travel inwards towards the mesogloea,
while the peripheral portion of the cell, on the contrary, becomes raised
up. In this way the cells lose the flattened plate-like form which they
have in the expanded condition (Fig. 42, D) and assume each a shape
rather like a mushroom, the nucleus being lodged at the base of the stalk
(Fig. 42, F).

When a contracted Ascon expands again, all the above changes of
structure are repeated in reverse order. The gastral cavity appears in
the midst of the porocytes which at first form an epithelium lining it,
and as the expansion continues, the porocytes become separated and
isolated from one another, and then travel outwards to take up their
position in the wall and to form pores.

Contractility to a greater or less degree is found in all sponges,
but, so far as is known, it is only in the more primitive species of
the genus Clathrina that it is carried to the extreme degree of
obliterating the gastral cavity, and so producing a condition com-
parable to the pupal stage in the development (cf. Figs. 58, 2, and
63, B). In those species of the genus which have spicules project-
ing into the gastral cavity, contraction is never carried so far, while
in the majority of sponges the phenomena of contraction are only
manifested in the temporary closure of the pores and oscula, both
of which structures, but especially the former, readily disappear
and appear again. ‘The condition, however, in which an Olynthus
or any other sponge appears without osculum and pores is always a
temporary one.

i

To sum up the facts with regard to the structure of the
Olynthus, as found in a calcareous sponge, it is seen that its body
wall is built up of two distinct layers, and contains five kinds of cells
and their products ; namely—

(1) The dermal layer, divided into a more external contractile
stratum, the flat epithelium and the porocytes, and a more internal
parenchymal or skeletogenous stratum, the spicules and their cells,
embedded in a gelatinous ground substance.

(2) The gastral epithelium, consisting of the collared epi-
thelium.

(3) The wandering cells, which do not constitute a distinct
tissue or cell layer, but are found scattered in all parts of the body
wall. At certain seasons, some of these cells become germ cells ;
hence the wandering cells and the reproductive cells may be in-
cluded together under the general term archaeocytes.

It is possible to imagine, however, a still simpler type of
-Olynthus than this, one namely in which a skeletogenous layer has
not been evolved. The dermal layer would then consist of a single
layer of epithelium and of the porocytes. Such an organism
would represent the simplest conceivable type of sponge, and might
be termed the Protolynthus. A Protolynthus stage is recognisable,
as will be seen, in a contracted, pupal form, in the embryonic
condition of Ascons, but as a fully developed and functionally
active organism it is not known to occur, even as a transitory stage,
in the life-history of any existing sponge.

From the Olynthus as a starting-point we may now consider
the organisation of sponges in general.

(a) Canal System.—All the cavities of the body traversed by
the currents of water which nourish the sponge, from the time they
enter by the pores until they pass out by the osculum, are termed
collectively the canal system. In the Olynthus the canal system has
been seen in its simplest type. In other forms it may attain to a
high degree of complexity, but its general evolution can neverthe-
less be reduced to simple processes of growth on the part of the
primitive Olynthus (Protolynthus), resulting in a folding of the
wall, and accompanied by a restriction of the collar cells to certain
regions. In the gradual and continuous process of differentiation
three distinct grades or types of organisation can be distinguished
which, though connected by numerous transitions, may yet be con-
sidered as three styles of architecture, so to speak, under which all
existing forms may be classified.

First Type of Canal System.—As an example of this type may be
taken the Olynthus itself (Fig. 43), of which the structure has
already been described. The parts of the canal system here are
pores, gastral cavity, and osculum.

This type of canal system is only found in Ascons amongst

SPONGES 31

32 SPONGES

Calcarea, and, as will be shown when these forms are discussed,
the Olynthus may undergo various processes of growth and folding
of the body wall without departing from this type, of which

the essential characteristic is that all the

2 OSC on canals and spaces between the pores and
i % the oscular rim are lined by collar cells,
‘iy q and by collar cells only; in other words, that
a) | G the gastral layer is continuous (cf. Figs. 65,66).

q = Second Type of Canal System.—This

type arises from the Olynthus, first by
a process of unequal growth and con-
sequent folding of the body wall, result-
ing in the formation of a number of
blind diverticula of the gastral cavity ;
and secondly, by the restriction of the
collared epithelium to the interior of the
diverticula in question, which are hence

ss
—

= Veto Gas <o=~
lv

JI
v

a
a
1
‘

Fic, 43.

Diagram of first type of canal
system (Olynthus). p, pores;
osc, osculum; G.C, gastral
cavity. The arrows show the
direction of the currents. In this
and in the next three figures, the
thick black line represents the
gastral layer, and the dotted por-
tion represents the dermal layer.

termed flagellated chambers (Fig. 44, A
and B). The central portion of the gas-
tral cavity becomes lined by a flattened
epithelium derived from the dermal layer,
and similar in all respects to the flat
epithelium of the external surface of the

body. Between the flagellated chambers,
which may vary considerably in form and length, canals are en-
closed along which the water flows to enter the chambers. From
their mode of origin it can be seen that the lumen of these incwrrent
canals, as they are termed, is simply a portion of the outer world
enclosed between the folds of the body wall, and lined by the flat
epithelium of the outer surface; and further, that the apertures
by which the water enters the chambers are nothing more than the
pores of the Olynthus.

At their first formation the diverticula of the body wall are
distinct one from another, and may remain so in a few instances,
but more often they tend to coalesce where they touch each
other, and also, by thickening of their outer or distal extremi-
ties, to form a cortex. In this way two sub-grades of the second
type can be distinguished. In the first (Fig. 44, 4) the incur-
rent canals are wide spaces, continuous with one another between
the chambers. In the second (Fig. 44, B) the coalescence be-
tween the chambers narrows the incurrent spaces to definite
canals, which commence by an opening on the outer surface of the
cortex. The sponge as a whole now no longer shows a folded
surface, but appears simply as if its body wall was greatly
thickened, thus reverting in form to the Olynthus type. The water
enters the incurrent canals by definite apertures on what is now the

j

outer surface of the body, which have the appearance of pores, and
are often so termed ; but it is obvious from the development that
the pores on the surface of the body in this type are not comparable
to those of the Olynthus, which are represented now by the chamber
pores. To avoid confusion it is best to employ a terminology which
distinguishes clearly between them, and hence the openings of the
incurrent canals may be termed the ostia, while the chamber pores
receive the special name of prosopyles. Similarly, the wide opening
by which the current passes out of the chamber may be termed the
apopyle.

The following parts can, therefore, now be distinguished in the
fully developed canal system of the second type (Fig. 44, B). The

SPONGES 33

Fic. 44.

Diagrams of the second type of canal system. A, simple type, with separate radial tubes.
B, more complex type, with radial tubes fused and thickened distally to form cortex and in-
current canals ; a portion only of the wall is represented. ost, ostia ; in.c, incurrent canals ;
pr.p, prosopyle ; fi.c, flagellated chamber ; ap.p, apopyle. Other letters as in last.

water enters through the ostia (dermal pores) into the incurrent
canals ; thence it passes through the prosopyles (chamber pores)
into the ciliated chambers ; and from them it passes by the wide
apopyles into the gastral cavity and out through the osculum. The
gastral layer, being restricted to the chambers, is discontinuous, as
it is in all types of canal system above the first type.

Third Type of Canal System.—The third type can be derived from
the second by a further process of folding of the body wall, giving
rise to bays or diverticula of the gastral cavity, into each of which
several chambers open together (Fig. 45, 4). Thus a system of
what are termed excurrent or exhalant canals becomes inter-
polated between the chambers and the gastral cavity proper.
In correspondence with this addition to the canal system the in-

34

current canals also become complicated and ramified. The whole
canal system may now conveniently be divided into three parts:
(1) The incurrent system, from the ostia to the prosopyles of the
ciliated chambers ; (2) the chambers themselves ; and (3), the ex-
current system from the chambers to the osculum.

The canal systems of the third type may become highly
differentiated and complicated in their several parts. Both in-
current and excurrent canals may branch repeatedly and undergo
various modifications in different regions. Quite apart from the
complications of these systems, three stages of evolution are to be

Diagrams of the third type of canal system (eurypylous). A, more primitive, with elongate
chambers, B, with rounded chambers. ex.c, excurrent canals. Other letters as in last.

observed in the relations of the chambers to the incurrent and ex-
current systems, by means of which canal systems of the third type
can be divided into three sub-types.

In the first and most primitive sub-type the chambers open
directly into the excurrent canals by their wide apertures or
apopyles, and receive their water supply direct from the incurrent
canals through the prosopyles' (Fig. 45, 4 and #). A canal system
of this type is said to be ewrypylous.

In the second sub-type the opening of the chamber into the ex-
current canal is drawn out into a tube, usually not of great length,
termed an aphodus (Fig. 46, 4, aph). The relations of the chamber

SPONGES | :

to the incurrent canal remain as before. A canal system of this
kind is termed aphodal.

In the third stage the chamber has, as in the last, an aphodus,
and in addition a delicate canalicule termed a prosodus interpolated
between the chamber and the incurrent canal (Fig. 46, £), and
derived, probably, by elongation of a prosopyle. Canal systems of
this kind are termed diplodal. .

Thus in the most highly differentiated type of canal system,
the following series of parts can be distinguished: ostia, incurrent
canals, prosodi, ciliated chambers, aphodi, excurrent canals, gastral

SPONGES 35

Third type of canal system. A,aphodal; B,diplodal. aph, aphodus; prs, prosodus. Other
letters as in last.
os

cavity, and osculum, and to these may be added further complica-
tions of the incurrent system which will be described when dealing
with the canal system in the different groups.

The diplodal canal system is regarded by some authors as con-
stituting a fourth type of equal value with the other three.

Osculum, Gastral Cavity, and Pores.—The gastral cavity, properly
speaking, extends up the exhalant canals and includes the cavities
of the chambers. This is obvious from the development of the
canal system that has just been traced. It is more usual, however, as
well as more convenient in most cases, to distinguish the cloacal cavity

' which opens by the osculum, and into which the exhalant canals unite to

36 SPONGES

pour their contents, as the gastral cavity proper, from the excurrent canal
system. In many sponges, especially the thin-walled tubular or sac-
like forms, the gastral cavity is wide and spacious ; in others, especially —
in marine or incrusting forms, it may be so much reduced by the thicken-—
ing of the body wall as to be scarcely distinguishable from the exhalant
canals,

It has already been seen (p. 23) that by folding or unequal growth of the
sponge, a false gastral cavity may arise, opening by a false osculum
(pseudosculum), and containing in its interior the true oscula which simu-
late the openings of the exhalant canals (cf. Fig. 35, B). Conversely, we
find in some Hexactinellids a flattening out of the gastral cavity and loss
of the osculum, in which case the openings of exhalant canals simulate
true oscula (Caulophacus, ete. Fig. 20). Hence it is not possible to
determine the nature of an excurrent opening by simple inspection, nor
even in many cases by its anatomical relations.

Oscula are very often defended in various ways ; for instance, by
fringes or palisades of sharp spicules, or by sieve-like plates or mem-
branes across the opening (Figs. 15 and 18). In other cases the osculum
can be completely closed by a contractile sphincter or diaphragm
(Figs. 7 and 40). The oscular aperture may be on the level of the
general surface of the body, or raised up to form a special oscular tube,
often of great length (Figs. 25, 26, 31), according to the requirements of
the sponge.

In the above account of the canal system a clear distinction has been
drawn between true pores and ostia. The former are found on the
surface only in the canal systems of the first type; in other types the
inhalant openings are always ostia. The distinction is not, however,
always maintained, and superficial incurrent apertures are often loosely
termed pores, without reference to their true nature. :

Primitively.the ostia are scattered over the whole free surface. They
may be restricted, however, to the upper surface, which bears also the
oscula, as in Tentoriwm (Fig. 31). In fan-shaped forms the ostia are on
one side, the oscula on the other, from which the condition with a
pseudosculum and pseudogaster is readily derived. In the boring
forms of Cliona and its allies the sponge is embedded in a calcareous
matrix, but sends lobes up to the free surface, some of which
bear the incurrent openings, others the oscula. In many sponges the
ostia are aggregated into special sieve-like areas, termed pore sieves,
Upgrowth of the edges of such a sieve has probably given rise to the
remarkable state of things in Disyringa (Fig. 26), the highest and most
specialised type of sponge so far as canal system is concerned ; a single
inhalant opening leads by a long incurrent tube into a sort of atrial
cavity, surrounding the body of the sponge and containing what appear
to be the true ostia. Like the oscula, the ostia also may be defended by
spicules or by special contractile mechanisms, often reaching in Demo-
spongiae a high state of elaboration in the so-called chones (see below).

Many authors have sought to homologise oscula and pores, often
meaning ostia, however, by the latter term. True pores, as will be seen,
are distinct from oscula in that the former are intracellular, the latter

a

-

intercellular, in nature and formation. On the other hand, the general
development of the canal system precludes any homology between ostia
and oscula, and the great difficulty often fonnd in distinguishing the two
sets of structures in some Demospongiae is clearly secondary. It should
be mentioned finally that in Euplectella and some of its allies parietal gaps
are met with in the body wall, leading from the exterior into the gastral
cavity (Figs. 15 and 18). These openings have, however, nothing to do
with the canal system, and appear to be simply an architectural adapta-
tion to the animal’s life-conditions,

SPONGES 37

(b) Skeletal System.—A. small number of sponges are entirely
without any supporting framework or skeletal structures. A few
others, mostly inhabitants of the deep sea, have, according to
Haeckel, a pseudoskeleton composed entirely of foreign bodies,
without any elements secreted by the sponge itself; the true nature
of the organisms in question is, however, very doubtful.

The vast majority of sponges, however, possess a true skeleton
(autoskeleton) composed of elements secreted by the sponge itself
(autophya, Haeckel), which may be supplemented to a greater or
less extent by admixture of foreign particles (enophya, Haeckel),
such as sand grains, skeletons of minute organisms, or spicules of
other sponges, taken up by the sponge from its surroundings. The
autoskeleton is always a secretion of the cells of the dermal layer,
and takes the form either of mineral sclerites or spicules, or of an
organic substance termed spongin, occurring usually either as a
cementing substance, or as fibres. The spicules may be composed
either of carbonate of lime in the form of calcite, or of colloid
silica (opal), with in each case a slight admixture of organic matter.

a. Spicules.—The morphological variations of the sponge spicule
are very numerous, and their classificatory importance necessitates
a complete and systematic nomenclature of the principal types of
form. Each spicule, of whatever material composed, is typically
made up of a greater or less number of rays or arms, representing
directions of growth, which radiate from the centre of the spicule,
ie. from the starting-point of the secretion, and are laid down
along a number of ideal axes. Theoretically, the number of rays in
a spicule will be either equal to, or double, the number of axes.
In point of fact, however, the number of rays actually present
may be far less than the number ideally possible for any given
type of spicule, either as the result of a secondary reduction of
spicule rays primitively present, or it may be, by persistence of the
spicule in a still more primitive condition in which the full number
of rays has not yet been acquired. Thus a spicule with three
morphological axes has typically six rays, but the number of the
latter may be reduced to two or three or even to a single one.

The number of axes which can be recognised in a given
type of spicule is expressed by adjectives terminating in “axon,”

38 SPONGES

combined with a Greek numeral, as ‘“‘monaxon,” “ triaxon,” etc.
The number of rays present, on the other hand, is connoted in a
similar manner by substantives terminating in “actine,” or by
adjectives terminating in “actinal,”’—for example, “ diactine,” or
“diactinal spicule.” The former series of terms is usually em-
ployed to express rather the ideal type of any given spicule, the
latter to describe its actual condition.

The following types of spicule can be recognised in sponges
generally, each type exhibiting in its turn innumerable variations :—

(1) The monaxon type of spicule, built upon a single axis, and
having therefore simply the form of a rod or needle (Fig. 47, a and
b). A monaxon spicule may be either monactinal (Fig. 47, b) or

Fic. 47.

Types of spicules (megascleres). a, rhabdus (diactinal monaxon); }, stylus (monactinal
monaxon) ; ¢, triactine ; d, tetractine (tetraxon type) ; e, hexaetine ; f, desma of an anomocladine
Lithistid (secondarily polyaxon) ; g, sterraster (polyaxon) ; h, radial section through the outer
part of g, showing two actines soldered together by intervening silica, the free ends terminating
in recurved spines, and the axis traversed by a central fibre.

diactinal (Fig. 47, a), the two rays in the latter case being placed
in the same straight line. The axis may be straight or curved
(Fig. 48, a, 0, ¢, ete.).

(2) The triaxon type, characteristic of Hexactinellids (Fig. 47, ¢).
The primitive spicule is laid down along three axes which cut one
another at right angles at a central point, producing a six-rayed or
hexactinal spicule, which may undergo a secondary reduction of the
rays ; but so long as more than one ray persists, it meets its fellow
or fellows at angles of 90° or 180°.

(3) The tetraxon type of spicule (Fig. 47, 7), which may be con-
sidered ideally as laid down along four radii of a sphere which meet
one another at equal angles at the centre. Hence the primitive
form is a tetractine, of which any three rays will appear to meet at
angles of 120°, when projected in such a way that the fourth ray

a

a ’ | .
SPONGES 39

appears as a point. In this type, however, the angles at which the
rays meet one another are subject to considerable variation, as well
as the rays themselves,

(4) The polyaxon type of spicule (Fig. 48, m, 7, 0), laid down
along numerous axes which typically radiate from a common
centre.

Subordinate variations of these different types will be described in
dealing systematically with the subdivisions of the Porifera. We may
mention here, however, one differentiation of the spicules which is often
of importance, the distinction, namely, between skeletal spicules or
megascleres, which by their union in various ways build up the general
supporting framework of the body, and flesh spicules or mucroscleres,

Fig. 48.

Types of spicules (microscleres). «and b, sigmaspire viewed in different directions ; ¢, toxa-
Spire ; d, spiraster ; e, sanidaster; f, amphiaster ; g, sigma; h, chela (isochela); j, one end of
another form of chela ; ik, 7, other forms of chela; m, spheraster ; 7, oxyaster; 0, the same, with
six actines; p, another, with four actines; q, another, with rays reduced to two (diactinal
monaxon); 7, tylote microrhabdus ; s, oxeote microrhabdus ; t¢, rosette.

which lie scattered more or less freely in the tissues. In many sponges
no such distinction can be drawn; in others the distinction is purely
functional, and in so far as it has any effect on the morphological
characteristics, affects only the size of the spicules. In some cases,
however, the difference of function in the two classes of spicules is corre-
lated with divergent morphological characters, so that the distinction
between megascleres and microscleres may become a perfectly sound
and useful one.

All spicules, whatever the material of which they are composed,
are deposited within cells, termed scleroblasts. The origin and
relations of these cells will be discussed below in dealing with the
histology; we may consider here the development of spicules

_ themselves, which shows important variations. In the first place, a

40 SPONGES

distinction must be drawn between true or primary spicules which owe
their first origin to a single mother cell, and secondary spicules which
can be traced back to more than one cell. Secondary spicules may —
be due either to a deposit, not of spicular nature (see below, p. 41),
of skeletal material upon a primary spicule ; or to union of several
primary spicules to form a spicular system. The latter are usually
many-rayed forms, such as the equiangular triradiate and quadri-
radiate systems of many Calcarea (see below, p. 107), in which each
ray represents a distinct primary spicule or spicular element, derived
from its own mother cell or actinoblast, and fused secondarily with
its fellows to form the spicular system. The distinction between
these primary and secondary spicules is, however, one entirely in-
dependent of their morphological characteristics, since in Demo-
spongiae the spicules, with few exceptions, whatever their form or
the number of their rays, appear to arise from a single mother
cell; while, on the other hand, many spicular systems in Cal-
carea have become secondarily monaxon in form. Nothing is
known with regard to the formation of the triaxon spicules of
Hexactinellids.

The development of a primary spicule is very uniform, and that of
a simple monaxon type may be described in general terms as a typical
example (cf. Fig. 49, h-n). The first portion to be formed is a
minute organic rod, placed near the nucleus of the secreting cell.
This is the rudiment of the organic axial thread, and round it is
deposited the mineral matter.

In calcareous spicules the organic axis is very slender, and
the mineral matter subsequently deposited is of a crystalline nature,
and almost, if not entirely, free from organic matter; the whole
spicule is enveloped in an organic sheath of the same nature as the
axial thread, and continuous with it at the apex of the spicule.
Sheath and thread are the oldest parts of the spicule, and probably
appear first as a minute cell vacuole in which a crystalline deposit
subsequently takes place to form the spicule round a denser central
portion which becomes the axial thread. The substance of the
vacuole, and consequently of the sheath and thread, is of the same
nature as the intercellular ground substance or mesogloea of the
dermal parenchyma.

In siliceous spicules the organic axis is relatively much larger and
more conspicuous. The mineral matter is deposited round it in con-
centric lamellae of colloid silica, alternating with lamellae of organic
nature. One such organic coat probably forms an outer sheath to the
spicule, which is not, however, so conspicuous as in calcareous spicules.
The organic portions of the spicules grow faster than the mineral
portions, so that the axial thread projects at the two extremities of
the spicule rays into the protoplasm of the secreting cell. Hence
each spicule when freed from organic matter represents an open tube,

SPONGES 41

with a minute lumen, the axial canal, formerly occupied by the
organic axis,

Although a true spicule arises as an intracellular deposit, it
usually greatly outgrows the mother cell, and may attain relatively
gigantic proportions, as, for instance, in the spicules of the root tuft
of Luplectella and Hyalonema. In such cases it is far from certain
how the later growth is effected. It is commonly assumed that
other scleroblasts attach themselves to the growing spicule and
deposit fresh mineral substance upon it. Growth of this kind
has, however, only been demonstrated in the case of the irregular
spicules known as desmas (see below, p. 134) of the Lithistida, spicules
clearly of a secondary nature. In Calcarea, on the other hand, the
whole growth of the spicule or spicular element is entirely due to
the activity of the original scleroblast and its descendants. The
mother cell divides into a greater or less number of formative
cells which spread over the growing spicule and build it up to the
required size. In other cases only the nucleus of the scleroblast
divides, and the spicule ray is enveloped in a nucleated plasmodium.
The later development of the spicules of Demospongiae has not
been studied, but it is probable that, as in Calearea, all true
spicules, whatever their size, are secreted entirely by the mother
cell or by cells derived from it.

When the spicule is fully formed the scleroblast, or at least
some of the formative cells derived from it, may persist, adhering
to the spicule after their secretive activity has ceased, as is always
the case in Calcarea ; or they may disappear from the spicule when
its growth is complete, as seems always to occur in the case of
siliceous spicules.

The above account of spicule development applies equally to the
individual rays of the secondary spicular systems in Calcarea, an
account of which will be found below (p. 107).

In addition to the secretion of mineral substance in the form of
spicules, secondary deposits of silica are formed on the desmas,
already mentioned of Lithistida, and in the form of cement, uniting
spicules together, in Hexactinellids. It is not known accurately in
any case how these deposits are laid down, but it is very possible
from the mode of their formation that they represent secretions of
a cuticular or extracellular nature, and are therefore very different
from the spicules.

A true spicule may, in short, be defined as an intracellular
secretion of skeletal material, formed either by a single mother cell,
or by a number of formative cells all derived from one such mother
cell.

8. Spongin is an organic substance allied to silk, but apparently

_of variable composition. It is generally stated to yield leucin and
glycin, but not tyrosin, when heated with sulphuric acid, and its

42 SPONGES

chemical formula has been estimated at C,,H,,N,O,. (Krukenberg),
According to Hundeshagen,! however, some spongin contains a
considerable percentage of iodine, while other varieties contain
chlorine and bromine. The iodine containing variety—“iodo- |
spongin ”—yields tyrosin when heated with H,SO,.

Spongin, as a skeletal element, occurs in two distinct forms ;
first, as a cuticular secretion of a tenacious but elastic cementing
substance which glues siliceous spicules together into a more or
less definite system of skeletal fibres ; and, secondly, in the form of
minute elastic fibrillae, secreted within cells, and furnishing a tissue
which may be compared to the elastic tissue of higher animals,
By atrophy of the spicules in the first case we obtain fibres of pure
spongin, as in the so-called horny sponges (see below, p. 139).

A remarkable property possessed by the spongin fibres of many
sponges is that of taking up foreign particles of various kinds into
their interior. Sand grains, sponge spicules, Radiolarian or Fora-
miniferan skeletons, and such like bodies which fall on to the surface —
of the sponge body, become included in the fibres, apparently by
adhering to the tip of the fibre at its growing point, where it is
continuous, in all probability, with the external cuticle of the sponge
body. The absorption of foreign particles into the spongin fibre is
therefore not so much a question of their travelling down into it,
as of their being passively surrounded by spongin as the fibre grows
upwards. The fibres may be so laden with sand grains and foreign
bodies that the skeleton appears made up of them, and the spongin
is scarcely visible. Sponge skeletons of this kind are termed
arenaceous. The habit of fortifying the skeleton in this way is one
which has been acquired independently by forms of diverse affinities,
and is perhaps to be regarded as a specialisation, as it were, of a
frequent tendency to form a false skeleton by inclusion of foreign
particles in the growing sponge body.

Spongin originates as a secretion of certain cells of the dermal
layer termed spongoblasts, which by their discoverer, Schulze, were
regarded as belonging to the connective-tissue system, but are now
more generally regarded as derived directly from glandular cells of
the external flat epithelium. The spongin fibres are formed as a
cuticular secretion of the spongoblasts, a fact which explains not
only the great similarity, if not identity, in chemical composition
that appears to exist between the superficial cuticle of many sponges
and the spongin of their skeleton, but also the fact that the two
may be directly continuous (Spongilla, Evans). The primarily
cuticular nature of spongin skeletons further renders intelligible
the frequent occurrence of a basal plate of spongin, serving for the
attachment of the sponge, especially in sponges belonging to groups
(e.g. Clavulina) in which a spongin skeleton is usually absent. In

1 Quoted from Lendenfeld, Zoological Record, 1895.

SPONGES 43

one such instance, Spirastrella decumbens, R. and D., upgrowths from
the basal plate, are said to give rise to a lamellar supporting skeleton
(Keller, 1891). Where an internal fibrous spongin skeleton exists,
it may be supposed to originate in the first instance either from the
upper surface of the sponge body by an ingrowth of spongoblasts
from the epithelium, or as an upgrowth from a basal spongin plate.
An origin of the first kind would explain the very frequent inclusion
in the fibres of foreign bodies of all kinds, which would be absent
in fibres derived in the second way ; two possibilities which appear
to be realised in the two orders of horny sponges (see below).

In the case of the elastic fibrillae, on the other hand, the secre-
tion is intracellular, and comparable to the formation of spicules
(see below, p. 50). We thus have an interesting case of a skeletal
substance being laid down either as a spicular (intracellular) con-
cretion or as a cuticular (extracellular) cement. These two forms
of spongin secretion run parallel to the two forms of mineral
(siliceous) deposits already mentioned.

It must be acknowledged, however, that the details of the secretion
of the spongin fibres still remain to be clearly investigated. Their
cuticular nature is inferred from the relations of the spongoblasts to the
fibres (see Fig. 50), and from the fact above mentioned of the similarity
and even continuity between fibres and cuticle.

The apparent parallelism between the secretion of spongin and of
silica suggests strongly the possibility of an interchange taking place
between these two forms of skeletal material, whereby one might become
substituted for the other in a given instance. Similarly in Acanthometridae
the siliceous skeleton of other Radiolaria is replaced by an Acanthin
skeleton (see Protozoa). Such a substitution is further indicated by
the spongin spicules of Darwinella (see below, p. 141), upon which investi-
gations are urgently needed to throw light upon this point.

An aberrant type of spongin secretion is said to occur in Stelletta
stemensi (Keller, 1891) in the form of spherical or oval bodies, each in a
follicle-like cavity surrounded by a layer of epithelial cells ; but some
scepticism is perhaps permissible as to the true chemical nature of these
bodies.

(c) Histology.—It has already been seen that the Olynthus of a
simple calcareous sponge is composed of five classes of cells; four
of these, namely, flat epithelial cells, skeletogenous cells, collared
cells, and archaeocytes, are found in all sponges, each giving rise to
several sub-classes. Porocytes have not, however, been recognised
as yet in sponges other than Calcarea as clearly as could be
desired.

(1) Dermal Epithelium.—In all sponges an external layer of
flattened epithelium is present, though it may apparently degener-
ate in places into a cuticular covering. With a few exceptions the
nature of this epithelium is remarkably uniform, consisting of a

6

44. SPONGES

single layer of flattened, plate-like cells (pinacocytes, Sollas), with a
large spherical or slightly compressed nucleus lodged in the thicker
central portion of the cell. Mutual contact between the cells pro-
duces a network, with polygonal meshes, of cell outlines, often
visible in the living condition, and usually demonstrable without
difficulty by means of the silver nitrate reaction. In a few ex-
ceptional cases the flat epithelium is ciliated, as in Oscarella,
Aplysilla, and perhaps in some other cases.1 It is often covered
externally by a cuticle secreted by the cells.

The form of the epithelial cells may become greatly modified, as has
been described, as the result of contraction, which may cause them to
assume a shape like that of a mushroom with a bulbous stalk—the so-
called flask-shaped or onion-shaped epithelium. In most cases this form
is only temporary ; in a few instances, however, it would appear to be
the normal form of at least a part of the epithelium, especially where it
is of a glandular nature. In Halisarca the epithelium of the outer
surface—but not that lining the canals—is curiously modified in connec-
tion with the abundant secretion of mucus with which this form covers
itself.

In the most primitive sponges, as has been seen in the Olyn-
thus, the dermal epithelium performs a variety of functions while
remaining a uniform layer of cells. Apart from the fact that in
the lowest forms the skeletogenous layer is recruited from it, and
that its cells may even secrete spicules while retaining their epi-
thelial position, the dermal epithelium commonly combines con-
tractile (neuromuscular) and glandular functions. Thus in the
Calcarea sphincters or specially contractile organs are formed simply
of ordinary flattened epithelium. In the Hexactinellida we have
no evidence of any contractility. In the Demospongiae the
primitive condition may be retained or may be superseded in the
higher forms by a differentiation of the cell elements corresponding
to a physiological division of labour. A separation is effected
between more internally placed contractile elements and a more
external glandular and protective epithelium proper, and since in
the latter the glandular elements may become further differentiated,
we have two new groups of cell elements arising from the primitive
epithelial cell.

The contractile cells or myocytes, Sollas (“contractile fibre
cells,” Schulze), are fusiform cells, lying below the epithelium, and
often forming contractile mechanisms in connection with the larger
exhalant or inhalant openings of the canal system. Such con-

1 Lendenfeld at one time figured in all cases the flat epithelium as flagellated, but
these flagella, with few exceptions, are to be regarded as ‘ phantasms of the living.”

2 The figures of the epithelium given by Schulze (1877) for H. Dujardini, and
by Merejkowsky (1878) for ‘“‘ H. Schultzi,” differ considerably.

SPONGES

45

a, .

46 SPONGES

trivances are very common in Tetractinellids, and in their most
elaborate form consist of a ring-like sphincter for closing the
aperture, and a layer of radially arranged elements for opening it.
In most cases only the sphincter is present. The cells resemble
those of the flat epithelium in all respects except in form and
position ; in fact, it must be confessed that the fact of their being
distinct and separate from the epithelium has often been assumed,
on the theory of a mesoderm, rather than demonstrated.

Distinct glandular elements are not marked out in Calcarea,
except perhaps in the more columnar form of the epithelium where
the sponge is in contact with the substratum. In Demospongiae
separate gland cells are often present, having, as has been said, a
peculiar mushroom-like form. These cells are of special interest,
since from them, it would appear, are derived the spongoblasts of
the spongin fibres, which by their secretion form a very important
addition to the skeleton.

The nature of the mushroom-like gland ceils has frequently been
misunderstood, it having been supposed that both the external disc-like
portion and the more internal stalk contained each a nucleus of their
own. In this way two cells were made out of one—an external flattened
cell supposed to belong to the dermal epithelium, and a more internal
glandular cell, decorated with processes of various kinds, considered
as mesodermal or “subepithelial” in nature (von Lendenfeld). The
external nucleus figured by this author is, however, non-existent, and the
whole cell belongs to the dermal epithelium. In many cases, indeed,
eg. in Calearea, the cells described as glandular are simply cells of the
flat epithelium in a contracted state.

The spongoblasts are found as a sheath or “mantle” investing
the growing spongin fibres. Each spongoblast is of columnar form
(Fig. 50), resembling a mushroom-like cell of the epithelium,
without, however, the terminal dise. In Dictyoceratina the spongo-
blast layer surrounding the fibres is said to be continuous with the
epithelium at the surface of the body, where the tip of the fibre
raises the outer skin. The question of the origin of the spongo-
blasts is one which is, however, urgently in need of renewed in-
vestigations, current theories being based more upon assumptions
than upon observations, as in many other questions of sponge
histology. When the spongin fibres are fully formed, the glandular
spongoblast mantle disappears, its cells becoming, according to
Schulze (1879), stellate cells of the skeletogenous layer.

Before leaving the epithelium there remains for consideration the
question of nervous elements in sponges, The existence of special —

1 Thus Merejkowsky (1878) describes in /a/isarca a muscular sphincter of fusi-
form cells not covered by the “syncytium”; in other words, composed of cells of
the flat epithelium.

‘

SPONGES 47

epithelial or sub-epithelial nerve cells has been affirmed by Stewart
(1885) for Grantia compressa, and by Lendenfeld (see especially [8]) for
various sponges. Sollas also cautiously suggested a similar interpretation
for certain elements observed in or near the sphincters of Tetractinellids,
and proposed for them the term aesthacytes. No proof was at any time
brought forward, however, as to the nervous nature of the structures in
question, and at the present day the existence of any special nervous
apparatus in sponges has become universally discredited, partly because
subsequent investigations have been unable to confirm the alleged dis-
coveries, and partly because some of the structures supposed to be
sensory receive a simpler explanation in another way. For instance, the
so-called “palpocils” and “synocils,” described in Calcarea by Stewart
and Lendenfeld, can easily be found in preparations of these sponges,
especially if mounted in glycerine, as already noticed by Lendenfeld

Fic. 50.

Growing spongin fibre, with spongoblasts attached (after Schulze). 550. spf, spongin
fibre ; sp.bl, spongoblasts ; Coll, collencytes.

(1891). They are nothing more than portions of the dermal epi-
thelium raised up into a tent-like elevation by the projecting ray

of a calcareous spicule, which has become dissolved in the preparation.

In the interior of the papilla thus formed are seen the scleroblast or
formative cells of the spicule, spread over the spicule sheath and running
up to the tip of the ray; and it is these elements, and perhaps some
others also, such as wandering cells, which have been erroneously
identified as sense cells.

In the Olynthus there can be no doubt that the flat epithelium
performs sensory functions of an elementary kind, but it exhibits as little
special differentiation for this function as it does for that of contractility.
In Calcarea generally the same state of things is found ; reaction to
external conditions is manifested both by the porocytes and by the flat
epithelium, but the primitive condition of the dermal layer in this group
makes it almost certain that nerve cells do not occur here. Of Hex-
actinellids nothing can be stated definitely either way. In Demospongiae
it is not possible to deny positively @ priori the existence of nerve cells,

48 SPONGES

for where contractile cells are differentiated, the existence also of special
nerve cells is at least possible. It can only be said that the existing

»)

statements with regard to sense cells in sponges are, for the most part, —
quite untrustworthy, both in matters of fact and observation, as well as —
of interpretation, and that a complete scepticism with regard to this —
point is not only justifiable, but even demanded, in the present state of

the question.

(2) Porocytes.—The description given above for the pore cells -
of the Olynthus may be extended, in its main features, to those of
all Calearea. The porocytes are large, coarsely granular, cells, very
contractile, and capable of considerable migration by amoeboid —
movement. The pore duct arises by an intracellular perforation,
In Heterocoela the porocytes form the chamber pores or prosopyles,
the so-called dermal pores being intercellular ostia. |

In Clathrinidae the pores are situated on the surface of the body, on
a level with the dermal epithelium, but in Leucosoleniidae and in the ~
allied Heterocoela (Sycon, Leucandra, etc.) the pore is placed at the inner —
end of a funnel-shaped depression, forming a short afferent canal, For
such cells Bidder (1) has suggested the term pylocytes,

j

The origin of the porocytes, from the dermal epithelium, and |
especially from that lining the oscular rim, has been described
above. In the latter region the same cell layer which furnishes |
porocytes gives rise also to sphincters or contractile membranes —
for closing the oscular opening, a fact which emphasises the con- |
tractile nature of the pore-forming cells. Besides their contractility, |
a remarkable feature of the porocytes is the readiness with which
they give rise to skeletal structures of various kinds. Thus in ;
Clathrinidae (and all Calearea?) the fourth or gastral rays of the
quadriradiate spicules are secreted each by a porocyte (see below, p.
108, Fig. 75, 4 and 5). Moreover, in many Calearea (e.g. Clathrina
coriacea, encrusting form) the porocytes pass into the gastral cavity
between the collar cells, and give rise to a cellular network ramify-
ing throughout the whole gastral lumen. The strands of the net-
work are composed of porocytes placed end to end, and the axis
of each strand contains a fibre which has the same staining
reactions as the sheaths and axial threads of the spicules. The
fibres appear to be formed as an intracellular secretion of the poro-
cytes, which in this way furnish an elastic framework for the
support of the delicate sponge body.

The porocytes were long overlooked or interpreted erroneously in
Calcarea, and great doubt still attaches to their existence in non--
calcareous sponges. A comparison with Calcarea would guide us to seek
for them in the prosopyles, but there is as yet no proof that the proso-
pyles in siliceous sponges are intracellular ducts. Most authors have
been unable to decide definitely as to the nature of the prosopyles, but

SPONGES 49

incline to regard them as ‘intercellular gaps simply, formed by the
epithelium of the incurrent canals dipping in towards an interval
between the collar cells. On the other hand, the dermal openings of the
incurrent canals in Demospongiae have frequently been described as
intracellular ducts, especially in very young specimens (Carter, Maas,
Delage). It is possible that the openings seen in these cases were those
of true porocytes belonging to chambers in direct contact with the outer
surface. That the ostia of the incurrent canals should be formed by
intracellular perforations of porocytes would be a fact very difficult to
interpret in the light of the general evolution of the canal system, as
sketched above.

It seems, on the whole, more reasonable to assume at present, until
the contrary has been proved, that in siliceous sponges also true (intra-
cellular) pores are to be found at the prosopyles. In that case the
prosodus would probably owe its origin to the elongation of a porocyte
and its duct, and variations in this respect would explain the contra-
dictory statements made in some cases (e.g. Oscarella) as to whether prosodi
are present or not. The question is one, however, which cannot be
settled without further investigation.

While the existence of intracellular pores, comparable to those of
Ascons, is doubtful in siliceous sponges, there seems no doubt that cells
comparable to the porocytes exist in a variety of siliceous sponges
the so-called cellules sphéruleuses of Topsent (in part; see below, p.
59). ‘The cells in question are of lobose, amoeboid form, densely packed
with refringent granules, which obscure the nucleus; they resemble, in
fact, the contracted porocytes of Ascons. They are very conspicuous cells,
and it is therefore remarkable that their pore-forming function, if they
possess any such, should not have been observed hitherto; precisely the
same fact was, however, true of Calcarea until quite recently, porocytes
having often been observed, but their relation to the pores overlooked.!

In many siliceous sponges some of the very granular cellules
sphéruleuses, which are here regarded as porocytes, secrete fibrils
of an elastic substance differing so little in its nature from the
spongin that cements the spicules, that it can only be regarded as
a variety of it (Loisel [10]). The cells in question, which may
be termed spongoblasts, are found sometimes isolated, sometimes
in groups, but most commonly in rows, like a string of pearls (Fig.
51, 4, a and b). The spongin makes its appearance near the

1 A possible theory of the porocytes would be that they were cells of the dermal
layer which in some cases have acquired a special ingestive or phagocytic réle in
addition to their other functions. Such cells would naturally tend to place
themselves near the openings through which the currents enter the sponge body,
and might eventually come to surround these apertures. This view would explain
not only the alleged differences, mentioned above, in the position of the pore cells in
calcareous and siliceous sponges, but would also explain their apparent absence in
many of the latter, where it must be supposed that the ingestive mechanisms remain
at a lower stage of elaboration. In support of the theory here put forward, it may
he pointed out that the porocytes of Calcarea entrap and ingest larger bodies, such
as Diatoms, which are often to be found in them.

7

|
nucleus as a minute spherule easily distinguished by its staining :
properties from the ordinary cell granules. The spherule grows in
length and becomes a rod. The rods of neighbouring cells in each
string unite to form a jointed fibre, each segment being separated
from the next by an intervening substance less resistent to acids
and alkalis (Fig. 51, B). The secreting cells next become spindle-
shaped, and their contained rods become in consequence elongated _
and drawn out (Fig. 51, C and D). At the same time, their
substance acquires a denser consistence, more tenacious and less
soft. The result is a slender fibril, in which the segmentation
gradually ceases to be visible, enclosed in a protoplasmic sheath.
During this process the secreting cells gradually lose their

50 SPONGES

— ~

OU & =_=<=<=—

Fic. 51.
Diagrammatic representation of the formation of elastic fibrillae in the interior of spon |

blasts (porocytes?), after Loisel. A, spongoblasts, each containing a minute, rod-like y,
disposed irres zularly at a, arranged in a row at b. B, the rods are uniting end to end to form

a jointed fibril. C, later stage, the rods more elongate, and the cells now almost free from

spherules. D, fibril continuous, cells commencing to degenerate. £, fully formed fibril, with

adherent cell remnants ; 7, nuclei. .
(

spherules until they are left with a clear cytoplasm and nucleus
(Fig. 51, £). Finally, the fibrils come to lie free in the parenchyma, __
losing their enveloping cells, the nuclei of which appear to become
scattered in the ground substance. The whole process of fibril
formation is thus comparable to the secretion of the spicules, each
joint being formed in precisely the same manner as a single monaxon
spicule, while the whole fibril represents a number of spongin spicules
joined end to end, just as a triradiate calcareous spicule represents
asystem of monaxons joined at a centre. On the other hand, the —
secretion of these fibrils appears to be in every way comparable |
to the secretion by the porocytes of a fibrillar framework in the
gastral cavity of many Calcarea. It is therefore highly probable
that the cellules sphéruleuses represent the porocytes of Calcarea,

SPONGES 51

and originate like them from the dermal epithelium, from which
also arises the spongoblast layer, which by its secretion cements
the spicules together. It is possible that the porocytes in siliceous
sponges have only a skeletogenous function, and have not acquired
any relation to the pores, but this question must at present be
considered an open one.

(3) The Skeletogenous Stratum is developed to a very variable
extent in different sponges. Scarcely recognisable in some, in
others it attains great proportions, making up all but a relatively
insignificant portion of the total bulk of the sponge body. It consists
of a gelatinous ground substance or mesogloea (“ maltha,” Haeckel),
which contains cells of various kinds. The mesogloea is the first
portion to appear as a structureless layer between the dermal and
gastral epithelia, and is probably a secretion of the former. Cells
from the dermal epithelium next migrate into the mesogloea, form-
ing a parenchyma which is concerned primarily with the task of
furnishing skeletal structures for the support of the sponge body.

The separation, however, between the contractile (epithelial) and
skeletogenous (parenchymatous) strata of the dermal layer does not
amount to a very hard-and-fast distinction. As regards the function of
secreting skeletal structures, we find not only that so important a con-
stituent of the skeleton as spongin owes its origin apparently to cells of
the epithelium which have secondarily passed inwards, but that even
spicules may be secreted by cells of the epithelium which remain
in their primitive position, as in Leucosolenia, Spongilla, and
probably in many other cases. Further, in Ascons, and very
probably in all Calcarea, the skeletogenous layer does not grow by
multiplication of its cells amongst themselves, but their number is
recruited throughout life by immigration of cells from the dermal
epithelium ; how far the same is true of other sponges has not been
investigated. Hence the distinction between the epithelial and skeleto-
genous tissues is rather one dependent upon a gradual specialisation
of function, differing in degree from one species to another, than upon
morphological characters of fundamental importance, and there is no
reason from the histological point of view for regarding the skeletogenous
tissue as constituting a special layer or ‘‘ mesoderm ” possessing the same
importance or independence as the dermal or gastral layers.

The cellular elements of the parenchyma may be classified at
the outset into scleroblasts and connective tissue cells, the difference
between the two being primarily one of function, according, that is
to say, as a cell does, or does not, secrete a spicule. Of the two
classes of cells thus marked out only one may be present in a given
case. Thus in Ascons, and perhaps in Calcarea generally, con-
nective tissue cells are absent, and though they have frequently
been described, the cells which have been so interpreted are in
reality merely scleroblasts or formative cells which, in the process of

52 SPONGES

section cutting, have become artificially separated from their spicules.
In the Myxospongiae, on the other hand, the parenchyma consists
entirely of connective tissue cells, none of which secrete spicules.
The connective tissue cells or collencytes (Sollas) are marked out
by their clear protoplasm, free as a rule from coarse granules, and
by their fine thread-like pseudopodial processes (Fig. 49, a). In
both respects they usually stand in sharp contrast with the wander-
ing cells or amoebocytes, abundant, as a rule, in all parts of the
parenchyma, which in their more ordinary form are remarkable for
their very granular protoplasm and thick lobose pseudopodia, giving
the cell a form best compared to that of a potato. The collencytes
have been observed during life to be actively amoeboid, sending
out their thread-like pseudopodia and withdrawing them again.
The pseudopodia of two neighbouring cells may come into contact
and fuse temporarily. These changes of form may be accompanied
also by changes in the position of the cell as a whole (Schulze, 1877,
p- 16). Asa rule each collencyte has several processes, but in other
cases the number may be reduced to two, giving the cell a more or
less elongate, bipolar form. Hence the connective tissue corpuscles
may be distinguished as stellate and fusiform, the distinction being
in most cases merely a temporary one, correlated perhaps with a
particular position. By further specialisation, however, of one of
these two forms of cells, and the acquisition by it of a definite
form and characters, certain classes of tissue elements become
marked out. Thus in most Demospongiae there are found special
fibre cells or desmacytes (Sollas ; Fig. 49, d), derived doubtless from

bipolar collencytes, and furnishing the elements which bind the

spicules together into sheaves and fibres to form a continuous skeletal
framework or a special fibrous cortex. In other cases, again, the
’ collencytes—probably in the first instance those of the stellate
variety—acquire a vesicular structure resembling to some extent
the vesicular connective tissue found in many invertebrates. Such
cells are termed “cystencytes” by Sollas, and the tissue composed
of them, “cystenchyme” (Fig. 49, ¢).

According to the nature of either the cells or the ground substance of
the skeletogenous stratum, the body parenchyma may differ greatly both
as regards histological characters and consistence in different cases.
Sollas has distinguished a number of well-marked types of parenchyma
by appropriate terms : collenchyma, where the ground substance is abund-
ant, clear, and colourless ; sarcenchyma, where, on the contrary, the ground
substance is relatively less abundant and granular ; chondrenchyma (Fig. 49,
b), where the ground substance is dense and the parenchyma of cartilaginous
appearance ; and finally, cystenchyma, which has been mentioned above.

There remain finally for mention those elements of the dermal
layer which secrete the spicules. The scleroblasts when separate

es

SPONGES ) 53

from the epithelium, which, as has been said, is not always the case,
are usually at first rounded cells, within which a minute spicule
appears as an intracellular concretion (Fig. 49, /). As the spicule
increases in size it outgrows the secreting cell, which assumes the
form of a fusiform or stellate corpuscle apposed to the shaft, or
attached to the tip, of the growing spicule, and sometimes sending
out processes towards other cells (Fig. 49, 4, 7). If the spicule
formed is of large size, the cell, or at least its nucleus, commonly
divides to furnish two or more formative cells. In Calcarea, where
the scleroblasts migrate inwards from the external epithelium, they
at first resemble the epithelial cells in being very granular, but as
the spicule grows the granules gradually disappear, and at the same
time the nucleus decreases slightly in size. In Spongilla the spiny
microscleres are formed within cells of the flat epithelium which
have the usual granular nucleus, but the macroscleres are formed
within larger cells of the skeletogenous layer, of which the nucleus
is at first vesicular in structure, but afterwards becomes granular
(Evans). More than one scleroblast may combine together to form
a compound spicular system, as in Calcarea (see below, p. 108).

In Calcarea the scleroblast, or at least one of the two formative cells
derived from it, remains attached to the fully formed spicule. In
siliceous sponges, on the other hand, no cells have as yet been described
attached to the full-grown spicules, and hence it is probable that the
scleroblast Jeaves the spicule when its task of secretion is completed, as
occurs also in the case of one of the formative cells in the triradiates of
Clathrinidae. This fact may perhaps be correlated with the development
of a distinct connective tissue system in siliceous sponges, and its absence
in the Calcarea. In the latter the formative cells that quit the spicules
appear to go back to the external epithelium again [17].

(4) The Gastral Layer consists in all sponges of one kind of cell
and one only, the so-called collar cells, aggregated to form an
epithelium of a very peculiar and characteristic type, which fur-
nishes a continuous lining to all but a small part of the gastral
cavity, as in Ascons, or is broken up into discontinuous cell groups
lining the flagellated chambers (see above, p. 32), as in all other
known sponges. Each collar cell resembles, as has been said, a
single choanoflagellate monad, their most striking characteristic
being the possession of a protoplasmic collar surrounding the flagel-
lum, as described above for the Olynthus (cf. Figs. 52 and 53).

The variations of the collar cells or choanocytes of different sponges are
limited in their range as compared with the free living, and therefore
more adaptable Choanoflagellata. Differences are seen chiefly in the
position of the nucleus, in the relative size, shape, and structure of

* the collar, and in the size of the cell as a whole. The largest collar cells

are found in the Calcarea, and especially in the family Clathrinidae,

54 SPONGES

amongst which the species Ascandra faleata, H., is pre-eminent in this
respect, and may be taken as a type (Fig. 52, A). The cells in question
are columnar, and about half as long again as they are broad in the
fully expanded state. When contracted they become narrower and more
elongated, a change due to pressure of the surrounding tissues, and not

probably to the activity of the collar cells themselves (Fig. 52, B,c). The -

large nucleus is lodged at the base of the cell, as is always the case
in Clathrinidae, at least during the resting state of the cell. Each
choanocyte is in contact with its neighbours for about two-thirds of its
length, and the distal third forms a freely projecting “neck” (collwm),

Collar cells of various sponges. A, of Ascandra falcata, H. B, of Clathrina coriacea, Mont. ; oe
a, fully expanded ; b, less expanded ; ¢c, retracted down to hoop; 4, condition of aye
contraction. Cc, a, collar cell of Sycon re Fabr. ; 5, of Leucosolenia complicata,
D, a, collar of Halichondria panicea; 6, of Spongilla ; be, base of collar; Col, collar; ‘t
flagellum ; h, hoops ‘supporting collars ; n, nuclei. C, a, after Bidder; D, aand b, after Vosmaer
Pekelharing. D, x1000; A-C, x about 850 or 900.

bearing the collar (collare). The junction of body and neck is marked by
a distinct flange or “shoulder.” The base of the collar encloses a mound
of protoplasm continuing the neck, from the centre of which arises the
flagellum.

The cytoplasm has a very distinct alveolar or vacuolar structure, and
larger vacuoles—or it may be, one large vacuole—are commonly found at
the upper extremity, just below the flagellum, representing very probably
food vacuoles, by means of which the cell ingests food particles captured
by the flagellum. Contractile vacuoles have been frequently described
by older authors (e.g. James-Clark, the discoverer of the true nature of

SPONGES 55

collar cells, Savile-Kent, and others), but in more recent times they have
not been seen by any observer, and their existence must be considered
doubtful.

The cytoplasmic reticulum is clear and as a rule not very granular,
but usually contains one or more coarse refringent granules, similar to
those found in the dermal epithelium. There are commonly found also
a few irregular granulations, perhaps food particles. The nucleus is
rounded, slightly irregular in form, and always attached in Clathrinidae to
the surface of the cell. It contains usually a distinct nucleolus, and an
irregular, blotchy, nuclear reticulum.

The single flagellum is long, slender, and of even thickness throughout
- its length. It arises in Clathrinidae always from
a distinct granule of peculiar staining properties,
situated at the summit of the cell. When the cell
is fully expanded, the flagellum in preparation
appears homogeneous and difficult to see; but in
the contracted state it is dark, granular, and ap-
parently very brittle (Fig. 52, B,d). During life

<

Fic. 53.

Choanoflagellata, after Frauce. On the left, Codonosiga botrytis, J. Cl., x350, showing the
commencing transverse fission. In the middle, Salpingoeca fusiformis, 8S. K., x500. On the
right, Diplosiga Entzii, France, x 400. col, collar ; i.col, e.col, in Diplosiga, internal and external
collar ; 7, flagellum ; st, stalk ; th, theca.

it appears, in side view, to have a rhythmical stroke from side to side,
with a longer pause on one side than on the other; the beats in the
collar cells of Sycon are normally about ten to the second (Bidder).
Seen in surface view the flagella show a whirling movement, each one
moving quite independently of its neighbours (Vosmaer and Pekelharing
[30}).

The collar, the most characteristic feature of the cell, is in Ascandra
falcata a remarkable structure. When fully expanded it reaches a great
length, far exceeding that of the cell, and is supported by two hoop-like
thickenings or rings—one more proximal, which is very distinct, and one
more distal, usually less distinct (Fig. 52, A and Bb, h). At the base, up
to the first hoop, the collar is thickened and appears finely granular in
optical section ; beyond the first hoop it becomes much thinner, and its

,

56 SPONGES

distal extremity is often difficult to see, especially the actual opening. —

Hence these cells were at first described and figured by Carter and Dobie
as having three flagella—a larger median and two smaller lateral.
More usually the collar is found retracted down to the level of the second
(distal) hoop, which then appears thickened and easy to make out,
Frequently the collar is found still further retracted, and it often ends
at the first hoop (Fig. 52, B,c). In the extreme case of contraction of
the sponge, no collar is to be made out at all.

In Clathrina coriacea there appears to be but a single hoop, correspond-
ing probably to the proximal hoop of A. falcata ; and in Sycon, according
to Bidder, the collar is fluted, being supported by about thirty vertical
rods or thickenings (Fig. 52, C, a). Within the collar, at its base, Bidder
describes a sphincter-like thickening (hoop ?). In Leucosolenia the collar
cells are very similar to those of Sycon (Fig. 52, C, }).

In Choanoflagellata, Francé (1897) describes the collar as originating
by the folding round of a protoplasmic membrane or band, which runs
up the side of the body and is twisted in a spiral round the base of the
flagellum. Its structure could be imitated by twisting one end of a broad
paper band or ribbon into the shape of a funnel. Nothing of the kind
has been described in collar cells.

The details of cell division in the case of the collar cells have not as
yet been studied in full, but in Clathrina coriacea this process is initiated
by the nucleus travelling to the summit of the cell and taking up a
position beneath the flagellum. The nucleus then divides, one half
passes down, and the cell divides transversely to its long axis. The
upper half, bearing the original collar, grows a new basal portion, into
which its nucleus travels; the lower portion forms a new collar and
flagellum.

In ontogeny the collar cells—that is to say, the ciliated cells of the
embryo, which become the collar cells of the adult—have always the
nucleus near the distal extremity, and the flagellum arising directly from
the nuclear membrane, and passing out through the cell. This condition
is retained in the Leucosoleniidae and most Heterocoela, and is probably the
primitive state of things. When it occurs the larger vacuoles are found
at the base of the cell, not at the summit. In Clathrinidae, however, the
nucleus loses its connection with the flagellum, becomes attached to the
side of the cell, and finally travels down to the base, leaving behind it at
the upper extremity the distinct granule from which the flagellum arises,
representing, perhaps, a centrosome (cf. Fig. 58, 5). ‘It is interesting to
note that, as described above, each collar cell in this family when about
to divide commences by placing its nucleus in the primitive position at
the apex of the cell.

In siliceous sponges the collar cells are much smaller than in Calearea
and often excessively minute. In Halichondria the nucleus is apical, as
in Leucosolenia; in Spongilla, on the other hand, it is basal, as in
Clathrina (Vosmaer and Pekelharing),

Much discussion has been carried on as to the existence of a membrane
uniting the margins of the collars, described by Sollas in many Demo-
spongiae, and hence termed “Sollas’s membrane.” It was asserted by

SPONGES 57

Sollas that the edges of the collars became united by concrescence, giving
rise to a continuous membrane, perforated for the passage of the flagella
(cf. Fig. 54). Recent researches have failed to confirm these statements
(cf. Vosmaer, Pekelharing, and Bidder), and the appearances seen by Sollas
are attributed to defective preservation. The matter cannot yet be con-
sidered as settled satisfactorily.!

Before leaving the subject of the collar cells, it is necessary to mention
the frequently alleged transformation of collar cells and their subsequent
immigration into the parenchyma to recruit the ranks of other classes of
cells. Bidder (1891) formerly asserted the origin of porocytes in Ascons
from modification of collar cells, but this view is now hardly tenable in
view of the recent investigations which put the origin of the porocytes
from the dermal epithelium beyond a doubt (cf. Minchin [17]). More
recently Masterman (1894) has asserted that collar cells when full fed
become amoeboid and pass into the parenchyma as trophocytes (see below,

Choanocytes with coalesced collars (Sollas’s membrane), after Sollas. A, longitudinal
section through two flagellated chambers of Anthastra communis, Soll. ; B, diagram of the
fenestrated membrane produced by coalescence of the collars. i, prosopyles; c, aphodi; e, ex-
current canal ; m, Sollas’s membrane.

p. 58), and that further, after having distributed their nutriment to the
parenchymal cells, they take up waste products and migrate to the surface
of the body, where they act as nephrocytes. It seems more than probable
that these statements are founded on mistaken observations.

(5) The Archaeocytes represent in many ways the most important
cell layer of the sponge, but at the same time the one which, up to
the present, has been least studied. They are in their nature un-
specialised cells, scarcely modified in structure from the blastomeres
of the ovum, and capable of giving rise again, as sexual cells, to the
whole organism or, in the gemmules, to any form of tissue (ef.
Maas [12}). They stand, therefore, in sharp contrast to the tissue
cells, which, having assumed definite morphological characteristics
correlated with the performance of particular functions, are only
capable of multiplying to form other cells like themselves. The

1 Numerous descriptions and figures of collar cells have been published by Lenden-
feld at various times, but it is not necessary to refer further to them here.

58 SPONGES

archaeocytes correspond to the germ cells of other Metazoa,
but stand on a lower grade than those of any Enterozoa,
in so far as the germinal cells here are not idle cells, set apart
and biding their time to develop, but actually work for the whole
cell colony, performing elementary functions of digestion, distribu-
tion, and probably excretion, like leucocytes in other animals. In
sponges, to be brief, a leucocyte which has worked for the organism
may become a germ cell. In other animals leucocytes and germ
cells form two distinct classes of cells, though in Echinoderms at
least they appear to have a common origin.

In accordance with these important facts the archaeocytes may
be considered from two points of view: first, as wandering cells, or
amoebocytes ; secondly, as reproductive cells, or fokocytes. These two
categories are not, however, to be regarded as two distinct classes
of cells, but simply as two different phases in the activity of one
and the same kind of cell.

(a) Amoebocytes—The wandering cells of sponges are, as a rule,
easily distinguished from other cells of the parenchyma by their
lobose, rounded appearance, and the quantity of granules with which
their cytoplasm is usually packed, and which obscure the nucleus
in a general view of the cell. Very frequently more than one kind
of wandering cell can be distinguished, according to the nature
of the contained granulations, one kind having coarse, large
granules, the other fine granules, as in Clathrina contorta. Since
these granules are certainly to a great extent dependent upon the
state of metabolism of the sponge, these differences may correspond
only to variations in the functional activities of the same cell. In
other cases, however, differences of function appear to have led to
the establishment of well-marked and constant structural differences
between the cells, which may affect both nucleus and cytoplasm.
Thus in Spongilla, Fiedler (1888) has described two kinds of
wandering cells which he has termed “ Fresszellen” (phagocytes)
and ‘‘Nahrzellen” (trophocytes) respectively ; the former which
occur always near the free surfaces of the sponge body are
concerned more especially with the ingestion, and perhaps
digestion of food; the latter, found in all parts, appear to
provide for its distribution, To these two classes must be added
a third, belonging really to the class of trophocytes but specially
charged, apparently, with the function of storing reserve material,
and hence conveniently termed thesocytes (Sollas).

It is by no means beyond a doubt that the two classes of wandering
cells distinguished by Fiedler have exactly the function which he attri-
butes to them. The trophocytes frequently contain diatoms, and various
bodies apparently of the nature of food particles taken up by them;
hence their function may perhaps be phagocytic as well as trophocytie.
Fiedler’s phagocytes, on the other hand, may possibly possess an excretory

=

ft

SPONGES 59

function. Their evenly granulated cytoplasm and their superficial
position would both favour this view.!

The thesocytes in Spongilla contain a large vacuole filled with sub-
stance of an amyloid nature, and in addition a certain number of solid
amyloid grains. The presence of these substances is perhaps due to the
activity of the chlorophyll corpuscles which the cells contain, For an
account of their nature and their reactions to stains, etc., see Lankester
(1882).

The thesocytes probably correspond in part to the cellules sphéru-
leuses, a name by which Topsent seeks to distinguish a class of cells
found in all sponges, and frequently containing bodies of amyloid nature,
representing reserve nutriment. The possession, however, of “ spherules,”
i.e. of large refringent granules, is not one sufficient of itself to dis-
tinguish a class of cells. Topsent’s cellules sphéruleuses are certainly
porocytes in Ascons, and are probably the same in many other cases.
In some cases, however, they may represent thesocytes, ze. trophocytes
charged with reserve materials, Loisel [10] has shown that in Reniera two
classes of cellules sphéruleuses occur: (1) isolated cells containing nutrient
amyloid bodies ; (2) cells within which are formed the elastic fibrils.
The former, in our opinion, would be thesocytes, the latter porocytes.

The three possible differentiations of the amoebocytes or wander-
ing cells would therefore be ingestive cells or phagocytes, nutritive
cells or trophocytes, and finally, storage cells or thesocytes. It is
probable, however, that any wandering cell can perform each or all
of these functions, and that the characteristics by which one or
another of the different kinds of cells can be distinguished are
of transitory nature, and mark simply a passing phase of the

‘metabolism.

In addition to the large wandering cells, there occur in Ascons others
of excessively minute size, not more than four or five » in length, each
with a minute, faintly staining nucleus and clear cytoplasm. They
often occur in nests, as if they had originated from the breaking up of
larger cells, and it is possible that this is the manner in which the
ordinary wandering cells reproduce themselves in these sponges, and that
each of these minute cells is destined in its turn to grow into an ordinary
wandering cell. Their complete history is not as yet made out, but this
view receives some support from the fact (1) that cells are commonly to
be found showing every gradation of character intermediate between
these minute cells and the ordinary wandering cells; and (2) that the
numerous small cells produced in the ontogeny by breaking up of the
posterior granular cells pass in the young sponge into the condition of
these minute wandering cells (Fig. 58, 5, am.c).

(8) Tokocytes—From a purely histological point of view the re-
productive cells may be regarded as a form of thesocyte, a tropho-

1 Tt is not impossible that Fiedler’s phagocytes might be simply porocytes (cel/ules
sphéruleuses). Cf. footnote to p. 49, supra.

7

60 SPONGES

cyte in which the absorptive or anabolic power is increased, the
distributive or katabolic function largely in abeyance. When
special trophocytes exist, the tokocytes in their earliest stages
resemble them in all points, and undoubtedly belong to this class of
cell elements.

In sponges generally two classes of tokocytes can be dis-
tinguished : first, sexual cells or gonocytes, the mother cells of ova
and spermatozoa of the normal type; secondly, gemmule cells or
statocytes, such as compose the gemmule in Spongilla.

The gemmule cells will be discussed when considering the growth
and development of the gemmules ; it is sufficient here to say that they
arise from the same stock as the sexual cells, and that both in appearance
and potentialities they are comparable in every way to blastomeres of

Sperm cells of sponges. a-h, development of spermatozoa of Sycon raphanus, x792; h,
mature spermatozoa (after Poléjaeff); j, a sperm ball in Oscarella lobularis, x 500; k, a mature
isolated spermatozoon (after Schulze), x 800.

the segmenting ovum. We may consider more especially the origin of
the sexual cells.

The spermatogenesis has been studied in a number of forms, and
appears to conform to one of two types. In the first type of sper-
matogenesis, which has been especially studied by Poléjaeff in Sycon, and
by Fiedler in Spongilla, the male gonocyte or spermatogoniwm undergoes
a division of the nucleus into two dissimilar nuclei, one of which travels
to the periphery of the cell, while the other remains near or at the centre
(Fig. 55, a and b). The protoplasm then segments off in connection with
the peripheral nucleus to form a covering cell or spermatocyst surrounding a
sperm mother cell or spermatocyte. The former may remain single (Sycon),
or may divide again to form two covering cells (Spongilla). The sper-
matocyte undergoes repeated cell division by karyokinesis to form a
number of spermatids, each of which becomes a spermatozoon in the
usual way, the nucleus giving rise to the head, the cytoplasm to the tail.
The result is a mass of spermatozoa or sperm ball, enclosed by a covering
cell (Fig. 55, c, d, e, f,g). The second type of spermatogenesis is essentially
similar, but differs in the absence of any covering cell, the whole sper- —
matogonium giving rise to a sperm ball, which may be enclosed in an

a

SPONGES 61

adventitious envelope or follicle derived from the cells of the parenchyma
(Fig. 55, j). In Spongilla also the covering cells tend to disappear and to
be replaced by a similar adventitious follicle, which in this case may,
however, enclose several sperm balls.

Nothing has as yet been made out with reference to the interesting
phenomena of chromosome reduction, now so universally established in
other animals. To judge from Fiedler’s figures the number of chromo-
somes is small in Spongilla, apparently four in the germ cells and eight
in the somatic cells(?). The detailed structure of the spermatozoa also
remains to be studied.

The oogenesis and the maturation of the ovum has been studied
in Spongilla by Fiedler, and more recently in Sycon by Maas [15]. As
in other cases the history of the ovum may be divided into two periods—
the first of growth, the second of maturation. The ova are formed in all
parts of the body by growth of wandering cells.

In Spongilla each ovum becomes surrounded by a follicle formed of
cells of the parenchyma, amongst which a certain number of trophocytes
work their way. The trophocytes are concerned with the nutrition of
the ovum; it is remarkable, however, that the granules in the two
kinds of cells have different reactions, the nutriment received from the
trophocytes being worked up by the ovum into yolk granules, which
stain with blew de Lyon in the way characteristic of such granules, When
the ovum is full fed no more trophocytes are to be seen in the follicle,
which by the growth and pressure of the ovum has assumed an endo-
thelial character. The full-grown odcyte has a large germinal vesicle
containing a large central mass of chromatin or nuclear corpuscle.

During the maturation period the chromatin becomes concentrated
and individualised into chromosomes. Two polar bodies are given off in
the usual way.!

The fertilisation has been studied only by Maas in Sycon. |The
spermatozoon penetrates the ovum before formation of the second polar
body. The two pronuclei swell up and come together at the middle of
the long axis of the ovum. They then break up to form the first
segmentation spindle, in which maternal and paternal chromosomes can be
recognised side by side, and distinct from one another. The axis of the
spindle coincides with the longitudinal axis of the ovum. All subsequent
cleavages of the ovum are preceded by typical mitoses.

1 So Maas; Fiedler, on the other hand, describes the formation of the polar
bodies, as well as the cleavage of the ovum, as taking place by means of a peculiar
kind of direct division.

62 SPONGES

TABLE OF THE VARIOUS CLASSES OF CELLS.
E a tis (epithelial \
ells

2. eee ‘tes (contractile —
cells),

8. Gland cells.
4. Spongoblasts.
5. Pore cells.
6. Scleroblasts.
7

8

9

——e-

I. Epithelial stratum. |

. Collencytes (stellate
cells).
. Desmacytes(sibrecells),
. Cystencytes (bladder
cells) ;

10, Choanocytes (collar
{ cells

ae |
ll. aT (ingestive

V. Amoebocytes (wander- | 12. Trophocytes (nutritive —
; cells),

Dermal Layer. | II. Porocytes .

III. Skeletogenous stratum

a Layer . { IV. Gastral epithelium

Tissue-forming cells—Histocytes.

ing cells)
13. Thesocytes (storage
Archaeocytes (prt- cells). ;
mordial cells) | Statocytes (gemmule
}

VI. Tokocytes (repratetive | é cells).
cells), . “ti Gonocytes (sexual
cells),

Historical Review of Sponge Histology.—The earlier observers by teasing
up sponges with needles saw amoeboid cells and sometimes ciliated cells,
The discovery of the resemblance of the latter to Choanoflagellata was
made by James-Clark (1867), who, like most of his contemporaries, con- —
sidered sponges as Protozoan colonies. It was Leuckart (1854) who first —
drew attention to the architecture of the sponge as a whole, and com-
pared it to a Coelenterate. Haeckel (1872) formalised this conception,
and termed the two layers composing the body wall dermal and gastral
respectively. His names are adopted here in the same sense. The ~
dermal layer, which he termed “ exoderm,” and compared to the ectoderm —
of Coelenterata, was regarded by him as a syncytium, made up of fused
cells, the protoplasm of which formed the clear ground substance of the
parenchyma, while the nuclei with a small quantity of protoplasm
formed the corpuscles. The spicules arose by crystallisation in the
ground substance, a condensation of which around the spicule formed
its sheath. The gastral layer (‘“‘entoderm”) consisted of the collar cells,
from which arose the ova and spermatozoa.

Schulze in 1876 exposed the falsity of Haeckel’s syncytium theory
by the discovery of the flattened epithelium. Although this was a great
advance from the histological point of view, the conceptions of sponge
structure which Schulze founded upon it were less happy, and in many _
respects further from the truth, than Haeckel’s views. He considered the
flat epithelium to be partly ectoderm, partly endoderm, the collar cells_

———
—————

am

' It is possible that the phagocytes should be classified under the porocytes (see : ;
above, p. 49, footnote).

SPONGES 63

to be endoderm, and all non-epithelial tissues to be mesoderm. This
view, which for twenty years has been dominant, has in many respects
retarded our knowledge of the group, especially from the physiological
point of view, since it has led to cells of very diverse nature being
lumped together as mesoderm (see below, p. 85).

We reject here the mesoderm theory, both on structural grounds,
which have already been explained (p. 51), and for further developmental
reasons ; the fact, namely, that the so-called mesoderm, with the sole
exception of the wandering cells, does not represent a primary germ layer
set_apart once and for all in the embryo, but only a progressively special-
ised, and somewhat heterogeneous, portion of such a layer, which, in
Calcarea, as already stated, is continually recruited from the dermal
epithelium by immigration of cells. The view here adopted is nearer
to that of Haeckel ; sponges consist of a dermal layer (not a syncytium)
and a gastral layer, together with a number of archaeocytes, not recognised
by Haeckel. The homologies of these layers with those of other animals
are questions which require special consideration.

3. Leproduction and Development.

In sponges generally three modes of reproduction may be dis-
tinguished. The first of these may be termed vegetative reproduction,
and can only be distinguished from ordinary growth by its leading
to the formation of new individuals by budding instead of to a
simple increase in size in an individual already existing. The other
two methods are effected by means of special reproductive cells
(tokocytes), and may be distinguished as asevual, by means of
gemmules or special reproductive bodies, and sewual, by means of
ova and spermatozoa. ‘The first and third of these methods are
seldom absent, the second is less common.

(a) Vegetative Reproduction.—At the outset a distinction must
be drawn between cases where the new individuals produced are set
free (discontinuous budding), and where they are not (continuous
budding). In the latter case the budding is in many cases difficult
to distinguish from simple growth, and the distinction between the
two processes will depend on the criterion adopted of individuality in
the sponge organism (see below, p. 89). If the criterion taken be the
embryological one, and each osculum be reckoned as the sign of an
individual or sponge person, then the formation of a new osculum
in a sponge colony may be regarded as a case of budding, which
results in the addition of a new person to the colony. In some
eases where the persons, in this sense, are distinct and well
individualised, the term budding may be well applied, but in other
eases the distinction between growth and budding becomes rather
artificial.

Continuous budding, as above defined, is of almost universal
occurrence amongst sponges, except in forms with well-marked

i |

64 SPONGES

individuality, such as Huplectella and many other Hexactinellids,
and a few Demospongiae, in which, so far, it is unknown. Discon-
tinuous budding, on the other hand, is less common, though
sufficiently widely spread in all the main groups.

The formation of free buds is seen in its simplest forms in the
Ascons amongst Calcarea, and in Oscarella amongst Demospongiae. In
Ascons a portion of one of the tubes is nipped off as a small spherical
reproductive body, as described by Miklucho-Maclay (1868), though arbi-
trarily contradicted by Haeckel. In Clathrina buds are formed during the
extreme state of contraction when the tubes have become perfectly solid,
and the collar cells form a compact mass of rounded cells obliterating the
gastral cavity. Tubes while in this condition are often seen to assume a
moniliform-headed appearance, and each head or swelling breaks away
and becomes a free, solid, reproductive body consisting of an external
dermal layer, containing spicules and a central mass of rounded gastral
cells. After drifting dbout for a time the bud fixes itself, expands to
form anew its gastral cavity, and then by acquiring an osculum and
pores develops into an Olynthus. In the far less contractile Leucosoleniidae,
on the other hand, the reproductive body, formed in an essentially similar
manner by becoming nipped off from the extremity of a diverticulum, is
always hollow, its thin wall formed from the same elements as the wall
of the sponge. It fixes in the same way as the buds of Clathrina, and
develops into an Olynthus (Vasseur, 1878).

In Oscarella, according to Schulze, free buds are formed as papillae
protruded from the surface, which become nipped off as little vesicles,
each containing ciliated chambers, and surrounded by a flat amoeboid
epithelium, which sends out pseudopodia. The vesicle becomes fixed and
develops into a little sponge, apparently a minute Rhagon (see p. 125). Of
quite a similar type is the formation of free buds in Hexactinellids, the
result being the formation of a little Rhagon-like organism (Fig. 76),
which in Lophocalyx may acquire an osculum before separation from the
parent. In all these cases the bud is produced simply as a separation off
of a portion of the body, and contains all the layers and tissues which
enter into the composition of the parent organism. In Tethya, however,
the budding appears to be of a different type, and is better considered
under gemmule formation (see below, p. 67). It is of interest to note
that in many sponges with free buds special adaptations exist, derived
from the skeleton, for the purpose of extruding them from the parent
body. Thus in Lophocalyx (Hexactinellida) the buds are carried outwards
from the mother form by long spicules, which finally break off and set the
bud free. Similarly in Tethya the reproductive bodies are pushed out by
the growth of a long monaxon spicule, on the point of which the bud is,
as it were, impaled, and in like manner the buds of Aplysilla are carried
outwards on the tip of a spongin fibre.

The method of propagation by free buds has been successfully
imitated in sponge culture by artificial cuttings. The horny sponge of
commerce can be propagated in this way, but a considerable time is
required for the cuttings to grow into a large sponge.

SPONGES 65

(b) Gemmule Formation.—This method of reproduction, though
occurring also in many marine sponges of various groups (Topsent),
is seen in its most typical form in Spongillinae, where its details
have been carefully studied (see especially Zykoff [33]), and which
may therefore be taken as a type of gemmule reproduction.

The gemmules are formed in the late autumn as a protection
against the winter in Europe, but in the tropics they are more
usually formed at the commencement of the dry season, during
which the sponge is liable to desiccation. Each gemmule consists
essentially of a local aggregation of wandering cells, that is to say,
of trophocytes which become laden with refringent granules repre-

senting reserve material of the nature of food-yolk. A great

number of such cells, which may be termed statocytes, migrate by
their own activity into one spot in the skeletogenous parenchyma.
The cells of the parenchyma then secrete round them an adventitious
capsule forming the gemmule envelope (Fig. 56, 4, B, and C, i.ch.e).
The fully formed gemmule is a tough, seed-like body, and consists
of a densely packed mass of statocytes surrounded by a special cap-

‘sule. Each statocyte resembles in appearance a blastomere of a

segmenting ovum; its large vesicular nucleus can scarcely be made
out in the midst of the yolk granules with which the cells are
crammed (Fig. 56, V). In the simplest cases the capsule may con-
sist merely of a chitinous membrane; this may, however, be forti-
fied by the addition of a layer of spicules, which may be either the
ordinary microscleres of the parent sponge, as in Spongilla, or may
be composed of special spicules not found ordinarily in the sponge,
as in the case of the amphidiscs of Ephydatia (Fig. 56, amph).

The ripe gemmule is very resistent to vicissitudes of moisture
and temperature, and in Europe remains dormant until the spring,
the rest of the sponge dying away. The gemmules can be separated
from the parent sponge, and then give rise each on germination to a
tiny sponge individual; but in nature they seem more often to
remain entangled in the skeleton of the parent organism, and to
repeople it, as it were, on the approach of warmer weather, so that
the sponges seem to die in the autumn and revive again in the
spring. On germination the capsule bursts and the contents creep
out, forming an irregular amoeboid mass. The statocytes multiply
actively and become tissue cells of various kinds. The finer details
of the process of cell differentiation remain to be accurately studied,
but would appear to resemble in all essential points the transforma-
tion of the blastomeres into tissue cells during the embryonic de-
velopment. In fact, the gemmule is physiologically equivalent to the ovum
at the close of segmentation, i.e, to a mass of blastomeres enclosed in a
special capsule, and capable each of developing into one or another
form of tissue cell, with the difference, however, that the statocytes
are not derived like blastomeres from the segmentation of one

66 SPONGES

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Fie. 56.

Three stages in the development of a gemmule in Spongilla (after Zykoff). In A the amoebo-
cytes (statocytes), packed with refringent granules, are becoming aggregated at one spot, and
the parenchymal cells round them are taking an epithelial form and secreting an adventitious,
chitinous envelope ; still further away, the amphidiscs are being formed in scattered cells of the
parenchyma. In Bthe statocytes are densely packed and enclosed by the chitinous coat with
its secreting epithelium ; the amphidiscs are now passing between the cells of the latter. In
C the amphidises form a definitely arranged coat internal to the secreting epithelium, which is
now placed on the exterior, and is secreting a second chitinous envelope external to the amphidises.
amph, amphidises ; amph’, a young amphidisc ; i.ch.e, internal, and e.ch.e, external, chitinous
envelopes ; gl.ep, glandular epithelium ; ox, oxeote spicules of the sponge; par.c, parenchymal
cells ; st.c, statocytes or gemmule cells.

- 4
i:
.

overgrown gonocyte, but represent each a separate germ cell, which
_ has arisen independently of its fellows by modification of a wander-
ing cell.

SPONGES 67

It is evident that were a gemmule to be composed of a single enlarged
statocyte, a case would arise which would be difficult to distinguish from
parthenogenesis. Such seems, as a matter of fact, to be the true interpreta-
tion of the “budding” of Tethya, in which, according to Deszé, each bud
arises from one of a number of large cells, termed by him Sprosszellen
(germinating cells). Each Sprosszelle is contained in a capsule in the
cortex and gives rise by division to a multicellular reproductive body,
from which a small sponge develops like a bud on the surface of the
parent.

Gemmules, similar apparently to those of Spongillinae, have been
observed by Topsent in many marine sponges, not only in forms allied to
Spongilla (Reniera, etc.), but also in genera so far removed from it in the
system as Cliona and Craniella (Tetractinellida).

(c) Embryology.—All sponges, so far as is known, develop by means
of a ciliated larva, produced from a fertilised ovum which under-
goes, in all cases, a total or holoblastic segmentation.1 After swim-
ming freely for a longer or shorter period, the larva fixes itself and
undergoes a complete metamorphosis, after which it develops into
a young sponge, with pores and osculum, which commences to feed
and grow.

In Cliona, the boring sponge, the ova are extruded from the sponge
before segmentation has commenced, and go through their whole develop-
ment outside the maternal body. In all other known cases the ovum
goes through its early development, up to the formation of the larva,
within the maternal tissues. Hence the early development of sponges
may be divided conveniently into three periods : (1) The embryonic period,
from the ovum to the free swimming larva, usually passed within the
maternal tissue ; (2) the larval or free swimming period ; and (3) the
pupal period, from the fixation to the formation of pores and osculum.

There is scarcely any zoological problem which would appear, from a
study of the literature alone, to be so confused and difficult as the
embryonic development of sponges. The difficulty proves, however, to
be due not so much to the nature of the objects themselves as to the
many prejudices and preconceived notions with which they have been
studied. We may commence the account of this chapter in sponge
morphology with the life-history of a very simple and typical form, such
as Clathrina blanca, in which the adult structure is in all respects similar
to that of the Olynthus already described. The embryology of the
remaining types may then be studied from a general point of view, by
comparing, first, the various types of larva, and secondly, their meta-

. morphosis and organogeny.

1 For fertilisation see above, p. 61.

68 SPONGES

(a) Development of Clathrina blanca.—The ovum undergoes a regular
and total cleavage, resulting in the formation of a hollow, ciliated
blastula of oval form. The segmentation cavity is large, and con-

Fia. 57.

Development of Clathrina blanca seen as a living object with moderate magnification. 1,
larva seen in optical section; 24, pupal stage of the first day of fixation, metamorphosis
complete ; 24, a small portion of the same a few hours later, showing a distinct epithelium on
the surface ; 8, pupa at the commencement of the third day after fixation, showing the young
spicules and the gastral cavity beginning to form; 4, young sponge with pores and osculum,
of the fifth day. c¢.p.c, contracted porocyte ; fl.ep, flat epithelium; o.p.c, expanded porocyte ;
ose, osculum ; spic, spicule.

tains a coagulable fluid ; its wall is composed of a single layer of
columnar, flagellated cells, with compressed or onion-shaped nuclei.
At one point, the future posterior pole of the larva, are a pair of

,

SPONGES 69

very large granular cells with vesicular nuclei, which represent
undifferentiated blastomeres and are destined to give rise to the
archaeocytes, and therefore also to the sexual cells of the adult.
The flagellated cells, on the other hand, are the ancestors of all
the tissue-forming cells of the adult.

The larva is hatched either in this condition or by retardation
at a stage slightly in advance of it and swims freely for about

- twenty-four hours, first at the surface of the water and then near
the bottom. Meanwhile, a new class of cell-elements is being formed
by modification and immigration of individual cells of the flagellated
parietal layer (Figs. 57 and 58,1). Here and there a flagellated cell
is observed to retract its flagellum, while its nucleus undergoes an
alteration in shape and structure, becoming spherical, with more
evenly distributed chromatin and with a nucleolus. The cell at
the same time becomes more compact, draws in its more external
portion, and finally migrates from the body wall into the internal
cavity of the larva (Fig. 58, 1%-1¢). As the result of this process,
repeated often and at all points in the ciliated layer, with the
exception of the extreme anterior pole, the larval cavity becomes
filled with a mass of amoeboid cells, and the larva itself shrinks
‘considerably in size. By the second day the larva, which is now
ripe for fixation, has become a compact, planula-like organism, con-
sisting of three kinds of cells: (1) The external layer of flagellated
cells, destined to become the gastral layer ; (2) an inner mass of
amoeboid cells, the future dermal layer; and (3) the two still un-
changed posterior granular cells. Larvae of this type are termed
parenchymulae, and are found in the family Clathrinidae and in some
Heterocoela.

The larva fixes by the anterior pole, or by one side, and under-
goes a complete change of form and appearance, becoming a flattened
plate with irregular amoeboid contours (Fig. 57, 2+). In fact, at the
metamorphosis it resembles nothing so much as a small Amoeba,
whereas when free swimming it might have been mistaken for an
Infusorian. At first cell-outlines are not clearly distinguishable on
the surface, but towards the end of the first day of fixation the
surface can be seen to be covered by a distinct layer of flat
epithelium (Fig. 57, 2%). The metamorphosis of the larva, when
complete, is effected by means of radical changes in the relative
positions and functions of the different cell-elements of the body
(Fig. 58, 2). The majority of the cells of the inner mass of the larva
have passed out to the exterior and acquired a superficial position,
forming an epithelial layer, the future dermal epithelium enclosing the
formerly external ciliated layer. This reversal of position is effected
partly by dehiscence, the inner mass bursting out at some part of the
larva and growing round the disrupted ciliated layer, and partly by
diapedesis, the individual amoeboid cells struggling through the

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Fia. 58.

Development of Clathrina blanca as seen in sections. 1, larva; 1¢-1¢, four stages in the
modification and immigration of a ciliated cell into the inner mass; 2, section of pupa after
completion of metamorphosis (first day); 3, section of pupa on the second day. The immigra-
tion of cells from the dermal epithelium, to form the skeletogenous stratum, is going on pb
the porocytes are aggregated in the centre, and the gelatinous ground substance is making i
appearance. 4, section of pupa early on the third day. The gastral cavity, lined by porocytes,
and the spicules have appeared. 5, section of pupa towards the end of the fourth day, The
gastral cavity is lined by gastral cells, which are commencing to develop collars and flagella,
while their nuclei are migrating towards the bases of the cells. The spicules are large; the
position of the future osculum is indicated; the porocytes are migrating outwards ; and the
amoebocytes have changed in appearance. am.c, amoebocytes; cil.c, ciliated cells; G.C,
gastral cavity; ose, osculum; p.c, porocytes; p.g.c, posterior granular cells; skel, skeleto-
genous stratum ; spice, spicules.

ai

SPONGES 71

ciliated layer to the exterior. The epithelium of the upper surface
and edges is formed by the first method (overgrowth), that of the
central portion of the under surface chiefly by the second method
(undergrowth). The ciliated cells of the larva have lost their
characteristic form, becoming simply rounded, with an irregularly
shaped nucleus attached to one side of the cell; they lie huddled
together in a compact mass in the interior, and hence their flagella
are very difficult to make out. Scattered amongst the ciliated cells
are a certain number of cells of the larval inner mass which still
remain in the interior and are destined to become the future
porocytes. The greatest change is that undergone by the two
posterior granular cells, which have become broken up into a great
number of small corpuscles of peculiar aspect rather resembling some
varieties of leucocytes. Asa result of all these changes the pupa
at the completion of metamorphosis, i.c. towards the end of the
first day of fixation, consists of the following cell-elements: (1) An
external, flat epithelium, derived from the inner mass of the larva,
enclosing (2) a compact mass of cells, the formerly external ciliated
cells of the larva, amongst which are (3) a few porocytes, derived
from the larval inner mass, and (4) a great number of minute amoe-
bocytes, derived from the two posterior granular cells of the larva.

The subsequent development is comparatively simple. On the
second day of fixation the pupa becomes more compact, and by
drawing in its marginal pseudopodia, assumes the form of a bun or
cake (Fig. 58, 3). At the same time, a number of the superficial
dermal cells have migrated inwards from the epithelium and taken
up a position immediately beneath it, where they become grouped
in trios to form the triradiate spicules, which arise exactly as in the
adult (Fig. 58, 3, skel). In this way is initiated the division of the
dermal layer into the external contractile and the internal skeleto-
genous strata. The porocytes meanwhile have become grouped
together in the interior of the pupa. The results of these changes
are better seen on the third day (Fig. 57, 3), when the young spicules
beneath the epithelium have become very obvious ; and at the same
time the future gastral cavity has made its appearance as a more
or less irregular space, or spaces, in the middle of the centrally
placed porocytes, which at first form a continuous epithelium lining
the cavity (Fig. 58, 4).

Towards the end of the third day the further enlargement of
the gastral cavity causes the cells of the porocytic epithelium lining it
to become separated and isolated from one another, so that the
gastral cells come to form the boundary of the cavity. On the
fourth day the pupa has grown in height, chiefly by the develop-
ment of a now spacious gastral cavity, round which the gastral
cells form in most places a single layer (Fig. 58,5). The porocytes
are migrating outwards, and are found either between the gastral

72 SPONGES

cells, or to the outer side of them, in the dermal layer, so that they
begin to be visible on the exterior. The amoebocytes have assumed
one of the forms under which they occur in the adult, but their
further development has not been followed. The gastral cells begin
now to assume a columnar form and the collar and flagellum begin
to be clearly visible; they line the whole gastral cavity except at one
spot on the upper side, where they are wanting, and the body wall
is formed by the dermal layer alone, with an epithelium of porocytes
towards the interior ; this is the region of the future osculum and
oscular rim.

On the fifth day* of fixation the pupa becomes a young sponge
of more or less tubular form, with an osculum formed by a break-
ing through of the body wall, and with numerous pores, formed by
canaliculation of the porocytes which now are placed quite super-
ficially (Fig. 57, 4). The collar cells are well formed and functional,
and the sponge begins to feed and grow.

In the above development it will be noticed that all the events which
take place after the metamorphosis are similar to events which take place
constantly during the life of the adult sponge. The spicules are formed
by cells which immigrate from the external epithelium, exactly as in the
adult, and even the way in which the first porocytes are separated off by
the simple fact of their not migrating outwards, at the metamorphosis, in
company with the remaining cells of the dermal layer, may be regarded
as an abbreviation of the manner in which their numbers are subsequently
recruited from the dermal epithelium. The formation of the gastral cavity,
its relation to the porocytes, and the movements of the latter are repeated
in the same manner and order every time the adult sponge expands itself
after becoming completely retracted. In the same way the temporary
heaping up and consequent disfigurement of the flagellated cells during
the metamorphosis takes place also every time the adult sponge contracts
itself, and is not in any way comparable to the immigration of these cells
in the larva to form the inner mass, since in the former case no essential
histological or physiological change takes place in the cells. Hence it is
legitimate to compare the compact pupal stage which results from the
metamorphosis to the adult sponge in its completely contracted stage, and
it is evident that, were the pupa to expand itself at an early stage with-
out further differentiation of its component cell layers, we should have the
simplest conceivable form of sponge, one, namely, in which the body wall
was made up of a gastral layer composed of collar cells; a dermal
layer composed of flat epithelium and porocytes without a supporting
skeletogenous layer; and finally, amoebocytes (archaeocytes) scattered
about in the body wall.

A bird’s-eye view of the whole life-history, from ovum to
Olynthus, enables us to distinguish six distinct processes in the
development :—

1 Those dates represent what is probably the most normal course of events but are
liable to great variations in different larvae.

a rs

~

SPONGES 73

(1) Cell multiplication or segmentation of the ovum.

(2) Primary cell differentiation into tissue-forming cells (histo-
cytes) and primordial or reproductive cells (archaeocytes).

(3) Secondary cell differentiation or separation of the histocytes
into two primary germ layers (blastogenesis).

(4) Rearrangement of the cell layers in accordance with their
disposition in the adult (metamorphosis).

(5) Tertiary cell differentiation or tissue formation (histogenesis).

(6) Growth and acquisition of the body form (morphogenesis).

In Clathrina these six processes follow one another in the order
here indicated, the first and second taking place during the embry-
onic period, the third during the larval period, the fourth at fixa-
tion, and the fifth and sixth, more or less intermingled, during the
pupal period. We shall find that the great apparent differences be-
tween the various types of sponge development are in the main the
outcome of changes in the order in which these processes occur, and
in their relation to the three periods of development, such changes
being combined with specific or morphological characters of compara-
tively slight importance. For instance, all cell differentiation may
be thrown back to the embryonic period, thus coming to precede
the metamorphosis, and in such cases the larval period is rendered
barren, so far as developmental processes are concerned, and may
be greatly shortened, lasting only a few hours. In some Ascons,
on the other hand, e.g. Clathrina cerebrum, the pelagic larva may
swim at the surface for three or four days.

(8) Types of Sponge Larvae.—In the absence of any knowledge of
the developmental history of the Hexactinellids, we may consider
first the Calcarea and then the Demospongiae. A very instructive
evolutionary series is furnished by the larvae of calcareous
sponges, for which the larva of Clathrina blanca, described above,
may serve as a convenient starting-point.

The larvae of other Clathrinidae are parenchymulae very similar to that
of Cl. blanca, but exhibiting variations in two important features. In the
first place, the conspicuous posterior granular cells may vary in number
in different species, there being perhaps only one, or as many as four,
or even a yet larger number in some cases ; or, on the other hand, they
may be absent altogether, the body wall being made up entirely of
ciliated cells. The latter condition is due in reality to the cells in
question having become broken up into minute amoebocytes before the
larval period instead of after fixation, and in such cases the inner mass
of the larva contains two kinds of cells, which were regarded by Metsch-
nikoff as “endoderm” and “‘ mesoderm” respectively. It is interest-
ing to note that all these variations in the condition of the posterior
granular cells or amoebocytes may occur as abnormalities in one species
(e.g. Clathrina blanca).

In the second place, the apparent absence of posterior granular cells in

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SPONGES 75

tinually modified and pass into the interior, their place being filled by
the closing in of the ciliated layer. Thus three types of parenchymulae
can be distinguished in the Clathrinidae, which may be tabulated as
follows :—

Posterior Granular Cells. Immigration.
1. Present , ; : . Multipolar (Ex. C7. blanea).
2. Absent ‘ ; : . Maultipolar (Ex. Cl. cerebrum).
3. Absent : ; . Unipolar (Ex. C7. reticulum).

Fic. 59.

Types of sponge larvae, diagrammatic; the ciliated cells are left clear, the dermal cells

(inner mass) are shaded, the archaeocytes are granulated. ‘Transformation of ciliated (gastral)

_ ito dermal cells is represented by graduated shading. 1, larva of Clathrina reticulum ; 2,

newly-hatched larva of Leucosolenia (or pseudo-gastrula stage of Sycon); 3, late larva of Leuco-

solenia (or newly-hatched larva of Sycon); 4, larva of Oscorella (after Maas); archaeocytes

conjectural ; 5, larva of Myzilla (after Maas); 6, completely ciliated larva of a horny sponge ;
Spongilla is similar, but contains a cavity near to the anterior pole.

The type of parenchymula larva exemplified by Clathrina
reticulum (Fig. 59, 1) affords an easy transition to the so-called
amphiblastula larva found in Leucosoleniidae, and in the great
majority of Heterocoela. To understand the evolution of this type
it is necessary to suppose that in a normal parenchymula larva
with archaeocytes placed internally, and with immigration at the
posterior pole, the segmentation cavity has become greatly reduced,
and is practically filled up by the archaeocytes. The consequence
of this will be that the ciliated cells which become modified into

8

76 SPONGES

non-ciliated dermal cells at the posterior pole must remain where
they are, and do not immigrate into the interior. As the process
of cell modification continues, there is a constantly increasing
accumulation of rounded non-ciliated cells at the posterior pole.
The result is a larva with two sharply differentiated regions, an
anterior ciliated, and a posterior non-ciliated pole. Just such
a larva is found in Leucosolenia, in which, when newly hatched
(Fig. 59, 2), the non-ciliated region is absent or comparatively small,
but increases continually at the expense of the ciliated region.
Between the two regions is an equatorial zone of cells intermediate
in their characters, and in process of modification, and the centre of
the larva is occupied by the archaeocytes or central cells. The larva
swims about until it is about equally composed of ciliated gastral
cells, and non-ciliated dermal cells (Fig. 59, 3). It then fixes by the
anterior pole, and the ciliated cells are overgrown by the amoeboid
dermal cells. In other respects the development is essentially
similar to that of Clathrina.

From the larva of Leucosolenia it is but a slight step to the well-
known, but often misunderstood, development of Sycon. In this form
the ovum undergoes a total and regular segmentation (Fig. 60, a, d, ¢)
and produces a blastula, in which certain cells at one spot, the future
hinder pole, are marked out by their larger size, and darker granular
appearance (Fig. 60, d) ; these are the archaeocytes, comparable to the
posterior granular cells in Clathrina.1 The clearer cells (histocytes)
become columnar, and acquire flagella, while the granular archaeo-
cytes pass into the interior of the segmentation cavity, which they
nearly fill, and are completely enclosed by the clearer cells ; this is
the so-called pseudogastrula stage (Fig. 59, 2). The cells at the
hinder pole next begin to become modified in the usual way into
rounded non-ciliated cells, comparable in every way to those of the
inner mass of Clathrina, and the number of non-ciliated cells, at
first small, increases continually at the expense of the ciliated cells,
until the two kinds contribute to the composition of the embryo in
about equal proportions. At this stage, when the blastogenesis is
complete, the larva is hatched and swims freely ; it is made up of
columnar flagellated cells at the anterior pole, rounded, non-flagel-
lated cells at the posterior pole, and a central mass of granular
amoebocytes (Fig. 59, 3, and Fig. 60, ¢). During the free swimming
period the ciliated gastral layer becomes partially overgrown by the

1 The account here given differs from that of Schulze, who regarded these granular
cells as the future dermal layer ; for this reason Schulze distinguished the posterior
non-ciliated cells of the amphiblastula as granular cells (Adrnerzellen), from the
flagellated cells, though as a matter of fact the latter are in reality the more granular
of the two, since they contain yolk, which in the dermal cells becomes worked up
and absorbed more quickly. The statements here made are based upon my own ob-
servations upon Leucosolenia, and the figures of Barrois for Sycon and Grantia; see
also Dendy (1889),

—
—

z

non-ciliated dermal layer (Fig. 60, /), the cells of which may form
precocious spicules, so that both the metamorphosis and the histo-
genesis may be said to begin before fixation and during the larval

SPONGES 77

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Fic. 60.

Development of Sycon raphanus (after Schulze). a, ovum; b, c, ovum segmenting—b as seen
from above, c, as seen from the side ; d, blastosphere with eight (?) posterior granular cells
(archaeocytes), distinguished by their darker appearance ; e, free swimming larva (amphiblastula) ;
the more centrally placed archaeocytes are not seen; f, later stage of the same, showing the
ciliated cells becoming overgrown by the non-ciliated ; g, optical section of pupa in which the
gastral cavity has appeared ; note the two rounded cells, evidently porocytes, bordering on the
cavity; h, j, young sponge (Olynthus) showing the newly-formed osculum with an iris-like
contractile membrane from which the oscular riin is formed ; h in side view, j, seen from above.

period. If we compare this larva with that of Leucosolenia, as de-
_ scribed above, we see that it differs from it only in the fact that
the germ layer formation is thrown back, so to speak, from the
larval to the embryonic period, so that the Sycon amphiblastula

a

78 SPONGES

hatches in the condition in which the larva of Leucosolenia fixes
itself.

In the Demospongiae it is not possible as yet to trace so complete
an evolutionary series as in the Calearea, since the gaps in our know-
ledge are still very great. No larvae are known amongst Tetrac-
tinellids or Aciculina,! while amongst Clavulina only Cliona, and
amongst Dendroceratina only Aplysilla have been studied. On
the other hand, the life-history of some of the more primitive types,
such as Oscarella and Plakina, and of the Cornacuspongiae (Hali-
chondrina and Keratosa) have been the subject of careful investiga-
tions. As a convenient starting-point the development of Oscarella
may be selected.

Total and regular segmentation leads in Oscarella to the forma-
tion of an egg-shaped blastula, with a relatively thin wall which is
composed of a single layer of columnar flagellated cells. Over the
broader anterior half of the embryo the cells are shorter, and
consequently the wall thinner than over the narrower posterior
half ; the spacious internal cavity is stated to contain no cells. In
this condition the larva is born into the world, and swims freely
for from twenty-four hours to three days. The anterior half or
two-thirds of the larva is yellowish in colour, the posterior portion
carmine red, with a dash of brown. During the larval life the
differentiation of the germ layers takes place. The thin-walled
anterior half, the future gastral layer, remains unmodified. The
thick-walled posterior half, on the other hand, destined to become
the dermal layer of the sponge, is the seat of considerable change.
The cells in this region become more granular and of compact
cubical form, and a certain number of them retract their flagella,
become amoeboid, and immigrate into the internal cavity (Fig.
59, 4). The majority of the dermal cells, however, remain at the
surface, and retain their flagella, a point in which Oscarella differs
markedly from Clathrina, and which is correlated with the fact
that in the former the dermal epithelium is ciliated throughout life.
In consequence the internal cavity is very far from being filled up,
and the larva, though now comparable to an amphiblastula, remains
uniformly ciliated all over the surface. Observations upon the
archaeocytes remain to be made. ° The larva thus constituted fixes
by the anterior pole, and the gastral cells become invaginated and
surrounded by the dermal cells.

In Plakina the segmentation is total and regular, and the larva
emerges as an egg-shaped blastula of a rose-red colour, rather deeper at
the narrower posterior end. The body wall is made up of columnar

1 Since Cliona is known to extrude ova, which segment and develop into larvae
outside the body, it is possible that the same mode of development explains the
apparent absence of larvae in other Clavulina and in Tetractinellida, etc,

“SPONGES 79

flagellated cells (Fig. 61, «). During larval life the cells become modified
in their characters, and a certain number pass into the cavity, which is
filled, as is commonly the case in sponge larvae, with a coagulable

Fic. 61.

Development of Plakina monolopha. a, larva; b, section of the wall of the larva; ec, flagel-

_ lated cells; fl, flagella; col, coagulum, representing, probably, an albuminous fluid filling the

larval cavity, and containing immigrated cells of the flagellated epithelium ; c, early pupal stage

soon after fixation, the gastral cavity being formed by fission ; d, section across the foregoing ;

e, rhagon stage, with pores, flagellated chambers, and osculum ; the latter, not clearly shown

in the drawing, is in the slight promontory in the middle of the left side; /, part of a section

across a full-grown sponge. The attached basal layer is the hypophare; the spongophare

(see below, p. 126) is folded to form incurrent and excurrent canals. ov, ova (between two of
them a stage in the segmentation is seen); ¥/, blastulae. (After F. E. Schulze.)

(albuminous ?) fluid. The details of the blastogenesis and of the
. metamorphosis remain, however, to be investigated. It is probable that
they are, on the whole, similar to what occurs in Oscarella. In Halisarea
also the statements are conflicting, and the details of the development are

80 SPONGES

not very intelligible. According to Metschnikoff, the blastula becomes
filled at an early period by “rosette cells” (archaeocytes?). The larva
when hatched is solid, with an inner mass enveloped in a layer of
flagellated cells which show a differentiation at the hinder end of the body.
According to Barrois the development is similar to Oscarella. Not much
ean be drawn from the development of either of these important forms at
present.

In the Monazxonida and Keratosa a highly specialised but
essentially simple type of larva is found. The segmentation of
the ovum is total but unequal,! resulting in the formation of a
compact mass of centrally placed macromeres, completely or partially
surrounded by a superficial layer of micromeres (Fig. 62, 4). The
blastomeres next become differentiated in situ to form the larva.
The micromeres develop into the flagellated gastral cells. The

Fic. 62.

Two stages in the prelarval development of Chalinula fertilis. A, stage in the segmentation ;
B, later stage in which the histogenesis of the larva is advancing. mic, micromeres ; mac, macro-
meres ; ¢.c, Ciliated cells ; i.m, inner mass ; spic, spicules. (After Maas.)
macromeres, destined to become the dermal layer, do not re-
main uniform in character, but assume the structural peculiarities
of tissue cells of the adult, such as scleroblasts, contractile cells,
epidermic cells, etc., some finally remaining undifferentiated as
amoebocytes (Fig. 62, B). In short, both blastogenesis and _histo-
genesis take place during the embryonic period. The larva when
set free has an enveloping layer of flagellated gastral cells, distin-
guished from the other cell-elements by the minuteness of their
nuclei, and either completely enveloping the inner mass (Dictyo-
ceratina, Spongilla; cf. Fig. 59, 6), or leaving it exposed at the
posterior pole (Halichondrina, Cliona ; ef. Fig. 63, 4, and Fig. 59,
5).2 The larva is therefore perfectly comparable to a parenchymula

1 It may be doubted, however, if the unequal size of the blastomeres is really to
be explained as due to a process of meroblastic segmentation comparable to that
indneed by the presence of food-yolk in many Enterozoa, It is more probable that
it is simply due to the fact that the cells destined to give rise to the (smaller) gastral
cells divide up oftener than those destined to form (larger) dermal cells.

2 In Aplysilla the inner mass is said to protrude at the anterior pole (Delage).

a

or amphiblastula, in which histogenesis has early taken place. The
larval period is very short, and fixation takes place by the anterior
pole, the flagellated layer becomes broken up and surrounded by
the inner mass. The pupal period, being occupied almost ex-
clusively by changes of a morphogenetic nature, is also greatly
abbreviated. The flagellated cells of the larva become arranged
to form the chambers; the remainder of the sponge body arises
from the larval inner mass (Fig. 63, B and C).

SPONGES 81

Fic. 63.

Three stages in the development of Avinella cristagalli, Maas. A, longitudinal section of the
larva; B, early pupal stage soon after fixation ; C, late pupal stage shortly before the formation
of the osculum; one half only of the section is represented. i.m, inner mass ; ¢.c, ciliated
layer ; d.l, dermal layer; g.!, gastral layer; jl.ch, flagellated chambers ; can.syst, canal system.
(After Maas.)

(y) Metamorphosis and Organogeny.—Until the present decade it was
almost universally supposed that in all sponges except those with an
amphiblastula larva, such as Sycon, the ciliated layer of the larva
became the dermal epithelium (“ectoderm”) of the adult, while the inner
mass furnished the collared gastral epithelium (‘‘endoderm”) and the
connective tissue layer (“ mesoderm”), The only point at all disputed
was the origin of the flattened epithelium lining the gastral cavity and
the canals. Most authorities agreed with Schulze (1884) in deriving from
the “endoderm” the flat epithelium of the gastral cavity and of the

_ excurrent canals from the apopyles to the oscular margin, together with
the flagellated chambers themselves, The epithelium covering the exterior
and lining the incurrent canals up to the prosopyles was supposed, on the

82 SPONGES

other hand, to be “ectodermal,” and formed by flattening out of the
ciliated layer of the larva. This mode of interpreting sponge develop-
ment was more the result of @ priori reasoning than of actual observation.
The morphological similarities existing between sponge and Coelenterate
larvae on the one hand, and between adult sponges and coelenterates on
the other, led to the assumption that the metamorphoses of the larvae of
the two classes were also of an essentially similar type, a belief which was
seldom shaken by observation in the case of objects which present so
many technical and practical obstacles to microscopic study as do sponge
larvae. The development of Sycon alone stood apart, and was always
difficult to bring into line with the supposed course of the life-history of
other forms ; and it is greatly to be deplored that Metschnikoff, whose
accurate investigations first led to a true understanding of the develop-
ment of Sycon, should have failed to see that the metamorphosis of
Clathrina was of the same type.

In recent years the careful studies of Maas [11] and Delage [2]
have shown the metamorphosis of the larvae of Demospongiae to be
of quite an opposite nature to that of the Coelenterate planula,
though easily reconcilable with the development of such a form as

Sycon, since in both cases the flagellated cells give rise to the —

gastral layer, the inner, or posterior mass of typically non-flagellate
cells to the dermal layer of the adult. These observations have
been extended by the author to the parenchymula larva of calcareous
sponges, and by Maas to the blastosphere of Oscarella. There re-
main at present only Halisarca and Plakina as types in which
statements made under the influence of the older views remain
uncontradicted and in need of reinvestigation. The more recent
researches upon sponge embryology have made it possible, for the
first time, to give a consistent and connected account of the de-
velopment and to homologise the different types of sponge larva
with one another.

Development of Spongilla.—As an aberrant type of sponge development
it is necessary to mention that of the freshwater sponges (Spongilla and
Ephydatia). About no other form has so much been written; in no
other case are the statements so contradictory or the real facts of the
development still so obscure. The questions at issue concern the meta-
morphosis, and more especially the origin of the ciliated chambers of the
adult, on the one hand, and the fate of the flagellated cells of the larva
on the other. Thus, according to Ganin, the flagellated cells of the larva
become the “ectoderm” of the adult, and the chambers are derived from
the inner mass ; according to Gitte, the flagellated cells of the larva are
thrown off entirely, and the whole sponge develops from the inner mass ;
according to Delage, the flagellated cells of the larva become the ciliated
chambers of the adult, but in a roundabout manner, being first devoured
in a phagocytic manner by cells of the inner mass, which then carry them
inwards and cast them out again to form the chambers, some, however,
being entirely digested and absorbed during the process. Maas at first

a

-

took the view of Ganin, but later adhered to that of Delage, except as
regards the phagocytosis. Finally, Noldeke agrees with Delage that the
flagellated cells are ingested in a phagocytic manner by cells of the inner
mass, but believes them to be then completely absorbed, the whole sponge
developing, as Gitte supposed, from the inner mass alone.

The careful investigations, recently published, of Evans [34] show
that, as might be expected from a comparative survey of sponge embryology,
the flagellated cells of the larva do furnish the collar cells of the adult, but
that they may be supplemented in this function by other cells of the larva
in a very interesting manner, In the inner mass there are always to be
found large granular cells, similar both in appearance and potentialities to
blastomeres of the segmenting ovum or to cells of the gemmule, and marked
out by containing a large amount of reserve food material (nutritive
vacuoles and yolk-granules). These cells are to be regarded as archaeocytes,
which are able to give rise to tissue cells of any kind; while, on the one
hand, their destiny, so long as they remain unmodified, is probably to be-
come the amoebocytes of the adult, they may, on the other hand, in their

SPONGES 83

Fic. 64.

Five stages in the development of a flagellated chamber from a blastomere in the inner mass
of Spongilla. 1, a blastomere and two cells of the inner mass; 2, the nuclear corpuscle of the
blastomere has broken up into a number of chromatin bodies within the nuclear membrane ; 3,
the nucleus of the blastomere has become fragmented ; 4, the small nuclei so produced have
arranged themselves at the periphery of the cell, the cytoplasm of which is beginning to show
lines of cleavage between them ; 5, the original blastomere has broken up into a number of
collar cells, arranged in a chamber ; the two cells of the inner mass form part of the epithelium
of the excurrent canal. Slightly schematised. (After Evans.)

capacity of reproductive cells (tokocytes) contribute towards either the
dermal or the gastral layer. In the latter case they undergo a sort of
fragmentation, affecting first the nucleus and then the cytoplasm, and
resulting in the formation of a number of small cells, which, even during
the larval period, arrange themselves to form a flagellated chamber, each
cell acquiring the characteristic collar and flagellum (Fig. 64, 1-5). The
histological composition of the inner mass varies greatly, even in the
larvae of one and the same species of fresh-water sponge ; in some specimens,
chambers, in even their incipient stages of development, are almost or
entirely absent from the inner mass ; in others they occur abundantly and
in various stages of formation. In the latter case the flagellated layer
of the larva is perhaps partly absorbed at the metamorphosis, and the
chambers of the adult are derived chiefly from those of the inner mass of
_ the larva. In short, the development of Spongilla may take different
courses in different instances, the end result being, however, the
same in all cases. The way in which the chambers and other tissue-

7

84 SPONGES

elements arise from the primitive cells of the inner mass is exactly com-
parable to the origin of all the different kinds of tissue from the one kind
of cell-element contained in the gemmule, or to the differentiation of a
larva from the mass of uniform blastomeres derived from segmentation of
the ovum; and it is probable that this aberrant feature in the larval
development of Spongillinae is correlated with the acquisition by these
sponges of the method of reproduction by means of gemmules, the
peculiarities of which have been, or are being, acquired by the larvae also
to a greater or less extent.

The main features of sponge embryology may be summarised as
follows :—

I. The larva is composed of three classes of cell-elements: (1)
Columnar flagellated cells, forming the outer covering or localised
at the anterior pole ; (2) rounded, more or less amoeboid elements,
rarely flagellated, forming the inner mass or aggregated at the
posterior pole; and (3) the archaeocytes, usually scattered in the
inner mass and often represented by undifferentiated blastomeres.

(a) In the more primitive types the primary differentiation of
the cells is into (1) flagellated cells (histocytes), and (3) primor-
dial cells (archaeocytes), and the cells of the inner mass (2) arise
by modification of a certain number of flagellated cells, others re-
maining unmodified as the flagellated cells of the ripe larva.

()) In less primitive types the blastomeres of the ovum become
differentiated in situ into flagellated cells, archaeocytes, and cells of
the inner mass, the last named becoming still further differentiated
histogenetically before or during the larval period.

II. The larva fixes and undergoes a metamorphosis whereby
the flagellated cells become placed in the interior, while the cells of
the inner mass come to surround them completely.

III. (1) The flagellated cells of the larva become the collar cells of
the adult (gastral layer), acquiring a collar. No other tissue elements
arise from them, but some (or all?) of the ciliated chambers may
arise secondarily from undifferentiated blastomeres or archaeocytes
(Spongilla) ; (2) the inner mass gives rise to the dermal layer in its
entirety, that is to say, to the whole of the flat epithelium, the poro-
cytes, and the connective tissue layer of the adult ; (3) the archaeo-
cytes become the wandering cells of the adult, from which the
reproductive cells arise.

With regard to the transformation of larval flagellated cells into
the collar cells of the adult, it should be borne in mind that the
collar is specially developed when the sponge is actively feeding
and becomes completely retracted when at rest. Hence its absence
in the larva may be explained by the fact that the nutritive
functions are temporarily in abeyance. Taking this fact into
account, it is evident that the characteristic collar cells of sponges
are direct derivatives, only modified in unimportant details of shape,

g

SPONGES 85

and so forth, from the flagellated cells of the larva, which in their
turn are the earliest cells to be differentiated, and in the simplest
types compose the whole blastula with the exception of the archaeo-
cytes, the primitive germinal cells. The importance of these facts
from the point of view of phylogeny cannot be too strongly
emphasised.

Ill. THE PHysIoLOGY AND BIOLOGY OF SPONGES.

The most important organ of the sponge, from the point of
view of metabolism and nutrition, is the canal system. During life
and activity the flagella of the collar cells keep up a constant flow
of water through the sponge. The current enters at the pores or
ostia, streams through the canal system into the gastral cavity, and
passes out by the osculum. From the incoming current the sponge
obtains its nourishment and a supply of oxyen for respiration ; by
the outgoing current the waste products of metabolism are removed
from the body.

Although, however, the problem might seema simple one, there is no
question which has been so much discussed as the nutrition of sponges.
The confusion that prevails is very largely due to imperfect knowledge of
the structure of the sponge body. Since sponges are a group in which
the cells are largely lacking in co-ordination and show a corresponding
independence of action, it is evident that here physiology must to a great
extent wait upon histology, and that a clear understanding of the latter is
necessary before it is possible to form coherent ideas about the former.
Hitherto advances in the physiology of sponge nutrition have been greatly
hampered by an indiscriminate use of the word “mesoderm.” Since
under this term are commonly included cells so different in their nature
as porocytes, skeletogenous cells, and amoebocytes, it is clear that not
much is gained by ascribing this, that, or the other function to “ mesoderm
cells.”

With regard to the ingestion of food two opposite opinions have
prevailed, one set of investigators attributing an ingestive function to

.the collar cells, another set regarding the ‘mesoderm cells” as the true

phagocytes. Those who hold the former view explain the presence of
ingested particles in mesoderm cells as having been passed on to them
by the collar cells. The true explanation seems to lie, as Metschnikoff
(1892) has pointed out, between these two opinions. The “mesoderm ”
shows a great difference as regards its degree of evolution in different
types. While in some, eg. Ascons, the parenchyma is scarcely developed,
in others it reaches a high grade of complication. In accordance with
these differences the part played by the parenchyma in capturing food
may, in some cases, be very slight, in others very great.

There can be no doubt whatever, from the numerous experiments
that have been performed by various investigators, from Carter and
Lieberkiihn in the fifties up to Vosmaer and Pekelharing at the present

86 SPONGES

—— — See

time, that in many sponges at least the collar cells are very active in
capturing food. On the other hand, these cells are from their nature
and size incapable of ingesting large bodies such as Infusoria or Diatoms,
Food of the latter kind could only be absorbed by becoming entangled
in the webs of tissue in the incurrent canal system, there to be absorbed
by phagocytic wandering cells, or, it may be, by porocytes.

Considered generally, sponges present a gradual evolution as
regards the power of ingesting food materials, corresponding to the
evolution of the canal system. In the simplest forms, such as
Ascons, microscopic food particles are ingested by the collar cells
which line the whole gastral cavity ; larger bodies, such as diatoms,
may be captured by the porocytes, which close upon them like a
trap when they enter the intracellular lumen of the pore. The
collar cells represent, however, the chief “eating organ” of the
sponge, to use Carter’s expressive phrase.

In other sponges the complications of the incurrent system
represent a progressive elaboration and perfection of an apparatus
for assimilation, doubtless, in the first instance, of bodies too large
to be absorbed by the collar cells. As the water passes through
the inhalant canals and spaces, food in it is captured by cells in
the parenchyma, either by phagocytic amoebocytes, or, perhaps,
also by porocytes. The function of ingestion may finally be
usurped almost entirely by cells in the parenchyma ; the collar cells
then become concerned only with the production of the current,
their ingestive activities being in abeyance (Metschnikoff).

It should be added that, according to the investigations of
Loisel [10], some sponges, at least, are able to absorb nutriment
in solution, as well as in suspension. The cells of the epithelium
exercise in such cases a selective power, well shown by experiments
with stains acting infra vitam; some substances are permitted to
pass through the epithelium into the parenchyma, while others are
excluded.

Digestion is in most cases intracellular, ingested bodies being
absorbed within cell vacuoles, as in Protozoa. It is possible, how-
ever, that, in the case of bodies too large to be so ingested, a kind
of intercellular digestion takes place. Lieberkiihn, whose accuracy
us an investigator is above suspicion, saw Infusoria surrounded by
wandering cells in the canals of Spongilla, and there gradually
absorbed.

Cirewation and distribution of nutriment is effected partly by
wandering cells, partly, there can be no doubt, by the mesogloea,
which acts as an internal medium between the cells and tissues,
Loisel compares the mesogloea from the physiological point of view
to the interstitial lymph of higher animals. Substances, either —
solid or fluid, are cast out into it from the cells, and then taken up —
again by other cells. On the other hand, the transport, especially

’

: SPONGES 87

of solid materials, is effected largely by the wandering cells, which
are capable of active migration.

Excretion in sponges is still a disputed point. Bidder ascribes it to the
porocytes. Other authors attribute this function to the choanocytes, especi-
ally in those forms in which the parenchyma is most active in the capture of
food. Loisel regards the mesogloea as performing the function of excretion
by its own activity. Vacuoles and lacunae containing matter to be excreted
arise in it and are emptied to the exterior by contractions of the mesogloea
itself, aided by cell contractions. The matter must at present be considered
very doubtful. There can, however, be little doubt that the wandering
cells play a considerable part in excretion as well as in other functions.

Animal Functions.—Sponges in correspondence with the absence
of a special nervous system show a great lack of co-ordination in the
activities and moyements of their cells. Thus the flagella of the
collar cells do not beat in unison like the cilia of the epithelia in higher
animals, but each works independently of the others (Vosmaer and
Pekelharing [30)]).

Sensitiveness to external conditions is often exhibited in a marked
degree, but in such cases each cell placed superficially possesses this
quality equally, and there is no class of cells marked out as sense
cells by the possession of special physiological or structural characters.
Contractility is probably a quality possessed by all sponges to a
certain extent, and in some it is greatly developed. In all cases it
appears to reside in the cells of the epithelial stratum of the dermal
layer. Bidder, however, regards the power of contraction as
largely due to elastic tension of the mesogloea, tending to bring about
a contraction of the sponge if not opposed by the activity of the
canal system. This, however, would hardly explain the epithelial
sphincters often present.

Loisel, as we have seen, considers the mesogloea not merely endowed
with passive elasticity, but as actively contractile. This would necessitate
a very different view of the nature of the ground substance from that
generally held, and requires confirmation before it can be accepted.

* Statements have sometimes been made to the effect that the current of
the canal system may be reversed and flow into, instead of out from the
osculum. If these statements are not simply due, as is very probable, to
erroneous observations, they might perhaps be explained, as Vosmaer and
Pekelharing suggest, as follows. If, in a sponge with several oscula, one
of them is pouring out a very strong current, it might act as a flue, so to
speak, and cause the current in the other chimneys (oscula) to stop or even
to flow inwards. The authors mentioned have also put forward a theory
of the cause of the current through the canal system different from that
generally adopted. According to their view the action of the flagella alone

_ is incapable of causing a definite and continuous current, since they are
not co-ordinated. The current which can be observed flowing out of the
osculum is brought about by the disposition of the pores and the oscular

4

88 SPONGES

tube, which act as valves respectively, the former favouring an inflow and
hindering an outflow, the latter having a contrary action. The beats of
the flagella cause alternating, negative, and positive pressures in the interior
of the canal system ; the former cause water to flow in at the pores, the
latter result in its ejection at the osculum, When the current is once well
started it draws, like a flue, and so favours-its own continuance, its action
being comparable to the fly-wheel of a machine. Closure of the pores at
once stops the current, without, however, causing any pressure in the
interior, which would be dangerous to delicate tissues. The irregular beats
of the flagella then simply cause eddies and vortices in the gastral cavity
or chambers.

Bionomics and Natural History.—Sponges have a wide range of habitat
and are found living under the most varied conditions of existence, from
the shore-line, where they are continually subjected to most violent
stresses and strains, down to the calm and placid environment of the
ocean abysses. The influence of these different life conditions is seen
especially in the body form and in the skeleton. Sponges living on mud
or ooze show a further adaptation in the form of an anchoring root tuft
(see above, p. 3). Fresh-water sponges require to be able to withstand
greater vicissitudes than marine forms, whose environment, however
boisterous, is more uniform. As an adaptation to life in fresh water we
may mention the gemmules already described. Many siliceous sponges,
belonging to families far apart in the system, have the power of excavat-
ing calcareous rocks or shells to form tunnels which they inhabit. The
Clionidae are the best known instances of this. It is not clear how the
perforation is effected. The sponge may in later life grow out of its
excavations and become simply an incrusting or massive form of the
ordinary type.

Animals so full of cavities as are sponges offer a shelter to many
other creatures, some of which are always found as commensals of sponges ;
as instances we may mention various Crustacea, e.g. Typton, Spongicola,
and Hydrozoa, e.g. Spongicola fistularis, F.E.S, (= Stephanoscyphus mirabilis,
Allman), found in Esperella, and Anthozoa, e.g. Palythoa (Figs. 19, 24).
Sponges themselves appear to be very distasteful to other animals and
are eaten by very few. Some Nudibranchs, however, feed on them
and may then mimic closely the sponges upon which they feed; as
instances of this we may mention Jorunna Johnstoni, which feeds on
Halichondria, and Rostanga coccinea, which lives upon red incrusting
sponges. Both these Nudibranchs resemble the sponges upon which they
respectively live, both in colour and in surface texture (see Garstang,
Conchologist, ii. 3 (1892); and Journ. Mar. Biol. Ass, iii, 3, p. 220).

The distastefulness of sponges often leads to a symbiosis between
them and other animals, especially crabs. Suberites commonly grows on
the shells of hermit crabs, and soon absorbs the shell, so that the crab
inhabits a cavity in the sponge. Other crabs cover themselves with bits
of sponge which they plant on their carapace, on which the sponge grows
and moulds itself. It is yery probable that the distasteful and highly-
smelling sponge protects the crab from the attacks of fish or cephalopods,
imparting to it, as it were, its own qualities.

SPONGES 89

Sponges protect their bodies, and especially their apertures, against
the attacks of intruders or enemies by fringes and palisades of spicules,
and also by excretion of poisonous ferments from the surface of the body
which have a strongly oxidising action (Spongilla, Loisel). It is perhaps
to this that the smell of sponges is due.

As competitors sponges are very dangerous enemies to animals which
feed in a similar manner, such as Lamellibranchs, since they grow over
their shells and starve them by forestalling their supply of food. In
oyster culture a method of preventing this is to grow the oysters on
frames, which are occasionally pulled up and exposed during a shower of
rain. The fresh water kills the sponges, but the oysters close their shells
and are unscathed.

No adult sponge is known to be sensitive to light, but this property is
often exhibited by the larvae in a marked degree. The larvae of Ascons
are positively heliotropic when newly hatched, and swim at the surface.
They then become indifferent to light for a time, which is followed by a
third period, during which they are negatively heliotropic and swim at
the bottom, previously to fixing themselves. The sensitiveness appears to
reside in certain highly refringent granules in the ciliated cells, which in
the amphiblastulae are aggregated at the inner ends. In many siliceous
larvae there is a patch of pigment at the hinder end, which the larva
tends to turn towards the light, with the result that the larva as a whole
moves towards the dark.

Individuality.—The discussion of the morphology and physiology
of sponges may well be terminated by attempting an answer to the
question: What constitutes the individual in a sponge? The
most divergent views have been expressed on this point.

The opinions that have been put forward with regard to the
constitution of the sponge body by different authors depend, of
course, largely upon the views held by them as to the affinities of
the group (see below, p. 158). While most of the older writers
regarded the cell as the unit of individuality in a sponge, more
recent scientific opinion has sought to identify the sponge person
with some form of cell aggregate—namely, either with the flagellated
chamber, or with so much of the canal system as is centred round
a single osculum.

The older observers regarded the sponges as Protozoan colonies, con-
sisting of an aggregate of amoebae or Infusoria (Perty, Dujardin, Lieber-
kiihn, Carter, and Savile-Kent), until the discovery by James-Clark (1867)
of the collar cells, and their resemblance to Choanoflagellata, led him and
others to regard them as a colony of Choanoflagellata. This view was
taken up by Savile-Kent and Carter, the latter terming the collar cell the
“spongozoon.” At the present day these views and the controversies to
which they gave rise have little more than a historical interest.

The view that the sponge person was represented by the flagellated
chamber, held at one time by Carter, has its chief advocate in Haeckel,
and is based upon a theoretical interpretation of the origin of the canal

90 SPONGES |

system, We have seen that all the forms of canal system originate, in
theory, if not in fact, by a folding of the wall of the original Olynthus,
and that the flagellated chambers represent primitively diverticula of the
body wall. Haeckel interprets this folding as a process of bud-formation,
each fold representing a distinct individual, comparable to the original
Olynthus from which it arose. In this way an Olynthus becomes in
Ascons divided up by a process of gemmation into a number of incompletely
separated individuals, united by a common osculum, and each diverticulum
represents a bud, capable of becoming a new individual. A Sycon is an
Olynthus which has undergone strobiloid gemmation, each radial tube being,
as it were, a replica of the original Olynthus. At first (1872) Haeckel
did not extend this theory beyond the second type of canal system, as seen
in Sycons, and considered in the case of the third type (Leucons) that the
canals arose simply by branching of the pores of an Olynthus with a greatly
thickened wall. Hence in Leucons the osculum alone was supposed to
be the mark of individuality. But since it was abundantly proved that
the chambers in the third type of canal system were strictly homologous
with those of the second type, Haeckel later (1889) extended this theory
to Leucons and other sponges. In all alike the flagellated chamber was
regarded as the individual produced by budding and comparable to a
diverticulum of an Ascon or to the whole of an Olynthus.

In considering this view we may first take it as proved, not only that
the flagellated chambers of the second and third types are strictly homolo-
gous one with another, but also that they are perfectly comparable with a
diverticulum of an Ascon (see above). Any interpretation, therefore, of
the morphological nature of the one applies also to the other. That
being so, we may limit the scope of our inquiries to a consideration of
the question, how far the diverticula of Ascons can be considered as
buds. It is certainly true that each such diverticulum may grow out to
form a new individual, with its own osculum, The question is, whether
the diverticula in all cases are to be regarded as reduced buds, developed
from the first as such, or whether, on the contrary, an outgrowth repre-
senting a simple fold of the body wall, may not have taken on the
functions, so to speak, of a bud, %. of producing new individuals, The
answer given will depend entirely on the theoretical conception adopted
as to what constitutes budding, but it certainly seems a more natural and
less strained interpretation of the facts to regard the diverticula simply
as the result of a process of growth which results in the first instance in
an extension of the body wall and an increase of the absorptive surface,
and which may lead, in Ascons, to the formation of new individuals, but
which in Sycons and other sponges does not, as a rule, do so. The
gemmation theory leads in Ascons to a very artificial conception of the
morphology of the sponge in cases where the diverticula anastomose into — .
a network, as in Clathrinidae. Such a form as Clathrina reticulum
(Fig. 6), for instance, would then represent many thousands of individuals, _—
It seems more reasonable, therefore, even in Ascons, to reject. the view .

that the diverticula of the body wall are to be regarded primarily as buds.
In Sycons and Leucons this reasoning applies with even greater force, and
we are unable therefore to accept Haeckel’s theory of sponge individuality. _

i

SPONGES gt

The view that the osculum is the ‘sign of the individual, and
that a sponge consists of as many persons as there are oscular
openings, seems in every way the most natural conception, and it
is certainly the conclusion to which embryology leads. Whatever
the type of canal system, the metamorphosis of a single larva, or
the development of a free bud or gemmule, results in the formation
of a small sponge with a single osculum. Not until the osculum
is formed can the sponge feed and grow, and perform its usual
functions. The osculum represents, therefore, a physiological, as
well as a morphological, centre, and thus presents from several points
of view the most satisfactory criterion of sponge individuality.

Although, however, this view is theoretically the most feasible, it,
nevertheless, often presents practical difficulties of application in particular
instances. We have already seen that, on the one hand, a pseudogaster
may be formed by folding up of the body wall so as to enclose a space,
primitively external to the sponge, into which the true oscula may open
like excurrent canals into a true gastral cavity ; and that, on the other
hand, a true gastral cavity may flatten out so that the excurrent canals
may come to the surface and simulate oscula. In such cases the physio-
logical criteria fail to enable us to recognise the individual, and life-
history alone is a guide. Sponges offer great difficulties, in short, to any
theory of individuality, and more resemble plants than animals in this
respect. The primitively distinct and well-defined individuals become,
by increase of the body surface in a vegetative manner, mere growths,
zoa wmpersonalia, in which individuality is more or less completely lost.

IV. SysTeMATIC REVIEW OF THE CLASSES AND ORDERS
OF SPONGES.

Since sponges, with very few exceptions, possess a skeleton,

composed either of minute spicules of mineral substance, or of fibres

of organic nature, it is on the characters of this skeleton that the
principal divisions are founded. At the outset one class stands
apart from the rest, characterised by a skeleton in which the
material is calcareous. Amongst the remainder another group is
marked off with almost equal distinctness by the possession of
six-rayed spicules of triavon form. After the separation of these
two classes, termed respectively Calcarea and Hezactinellida, there
Temains a vast assemblage of forms, in which the most divergent
types are connected by such a complete and gradual series of inter-
mediate forms, that they must be classified together as a single
subdivision of the Porifera, equal in value to the other two. To
this class the name Demospongiae has been given, and it comprises
sponges in which the skeleton may be composed either of siliceous
spicules of various types, but never triaxon; or of fibres of a
horny substance, termed spongin, which occurs either pure or in

|

a

92 SPONGES

combination with siliceous spicules or foreign bodies ; or, finally,
sponges in which a skeleton is absent altogether. By means of |
these various characters the Demospongiae are further subdivided
into a number of smaller groups.

CLASS I. CALCAREA.

The caleareous sponges are a very sharply defined group of
the Porifera. No forms are known in the remotest degree inter-
mediate between them and the other classes. As their name
implies, their chief characteristic is the possession of a skeleton made
up of calcareous spicules, a feature correlated with many other dis-
tinctive points of organisation and structure which render a cal-
careous sponge easy of recognition.

From the point of view of evolution and morphology the
Calcarea are of special interest, since in all cases the starting-
point of the growth is the primitive vase-like Olynthus. The
characters of the adult sponge depend upon the particular manner
in which the Olynthus grows; and calcareous sponges furthest
apart in the system differ, in the Olynthus stage, only in the
same trivial characters of spiculation or histology which are found
in the adult as specific distinctions. The Calcarea thus present
a most valuable and convincing demonstration of the theory
of evolution. Nevertheless, the powerful attraction and stimulus
which they offer to speculative and imaginative intellects has not
been without its drawbacks, for in scarcely any other group is the
classification and nomenclature in so confused a state ; and it might
almost be said that as many systems of the Calearea have been
proposed as there are writers on the group. In spite, however, of
this diversity of opinion, no classification of the group has been
put forward as yet which can be considered in any way final ; and
the most fundamental problems of their phylogeny and natural
affinities are still in a very unsettled state.

Canal System.—Considered from the point of view of canal
system alone, the Calcarea are divisible into two grades. In the
first, the Homocoela or Ascons, are found the only known examples
of the first type of canal system (see above, p. 31). In the second,
the Heterocoela, corresponding to Haeckel’s two families Sycons and
Leucons, the canal system is of the second or third type. Thus in
the Homocoela, as the name implies, the gastral layer is continuous,
i.e. the collar cells line the whole gastral cavity ; in the Heterocoela
it is discontinuous and restricted to the so-called flagellated
chambers.

(a) The Canal System of the Homocoelaa—In the Ascons the
primitive Olynthus soon assumes a more complicated form, owing
to the growth of the body wall being localised chiefly in two

F

SPONGES 93

regions ; first, at the oscular rim, resulting in elongation of the
tubular body ; and secondly, at certain spots on the surface of the
body, leading to the formation of hollow diverticula or outgrowths
of the body wall. The diverticula grow out into tubes which
become branched and anastomose with one another, giving rise to
a more or less complicated network surrounding a central oscular
tube, which represents the original Olynthus (Figs. 2-7). New
oscula arise either by the perforation of the blind ends of diverticula
growing out from the tubar system in a vertical direction, or by
fission of a previously existing oscular tube. In the latter case the
oscular tube, or, it may be, the primitive Olynthus becomes first in-
folded on each side in a longitudinal direction, so that the transverse
section would have the shape of a figure of eight ; and then, by meet-
ing of the folds, two distinct oscular tubes are formed. In many
cases the fission of the Olynthus or oscular tube may stop short of
the osculum, so as to give rise to two tubes opening together by a
single oscular aperture, and a similar process of longitudinal fission
may bring about a multiplication of the tubes in any part of the
body. In the stalked species of the genus Clathrina, such as Cl.
blanca or lacunosa (Fig. 8), the tubar system arises chiefly by in-
complete fission of the Olynthus and of the tubes thus formed, and
searcely at all by the outgrowth and anastomosis of diverticula ;
the latter method is, however, the most usual in Clathrinidae, and
occurs always in Lewcosolenia.

The full-grown Ascon individual or colony consists of two parts ;
a more or less complicated tubar system (t.s), opening by one or more
oscular tubes (osc.t, Fig. 65). The gastral cavity is continued into all
the tubes, which are lined everywhere by collar cells, their wall
having in all parts the same structure as the primitive Olynthus,
from which they arose. Between the tubes spaces are enclosed,
which, as is obvious from their development, are really external to
the sponge. In these spaces, which have been termed the infer-
canal system (i.c), the water circulates before entering through the
pores into the gastral cavity.

Two distinct varieties of canal system can be recognised in Ascons
which are the result of slight modifications in the mode of growth, and
correspond to considerable differences in the external form. In the first
variety, characteristic of the family Clathrinidae (Fig. 65, A), the tubar
system is greatly developed, and the oscular tubes are comparatively
insignificant, acting as mere vents for the ramified network of tubes of
which the body is composed. In the second variety, characteristic of the
family Leucosoleniidae, the oscular tubes are large and conspicuous, and
quite overshadow the tubar system (Fig. 65, B). The latter appears

° either as a series of diverticula from the erect oscular tubes, or as a
system of narrow tubes uniting them basally like a stolon, and in both
cases branching and giving rise to new oscular tubes. In the Clathrina

94 SPONGES

type the sponge has more the form of a growth, spreading or compact,
without distinct individuals. In the Leucosolenia type the sponge appears
as a collection of distinct Olynthus individuals, each throwing out diver-
ticula on every side, from which daughter individuals arise by a process
of budding. In Clathrina the intercanal system is greatly developed ; in
Leucosolenia the term can scarcely with justice be applied to the inter-
spaces between the diverticula and oscular tubes.

In the family Clathrinidae the canal system, though always reducible
to the type above described, may undergo certain secondary modifications
which may be considered under two heads, according as they affect the
gastral cavity or the intercanal system. As an instance of the former
kind may be mentioned the frequent widening of the cavity of the

“
“4 \
“ y

e ee of canal system in Ascons. The thick black line represents the gastral layer, the
dotted line the dermal layer; the pores are not represented. A, Clathrina type; B, Leuco-
solenia type. osc.t, oscular tube ; t.s, tubar system ; i.c, intercanal system.

central oscular tube, until it assumes the appearance of a central cloaca
or basin, into which the Ascon tubes empty themselves.. This modifica-
tion has reached its limit in the species Clathrina tripodifera, Carter (type
of Bidder’s genus Dendya), as described by Dendy (1891), in which the
tubar system takes on a radiate arrangement round the very large central
cloaca. In the genus Ascandra, on the other hand, the gastral cavity is
divided up by folds of the gastral layer, which owe their origin to the
great development of the spicule rays which project from the wall into
the gastral cavity. The diverticula thus formed are not, however, in any
way comparable to those seen in the oscular tube of Leucosolenia, since in
Ascandra the folding does not affect the external surface of the body wall,
but only the gastral layer.

Modifications of the intercanal system in the simple Clathrina type

ee ee

SPONGES 95

take place chiefly in one of two ways. First, in compact forms the whole
sponge may be enveloped in a sort of outer covering or skin, termed a
pseudoderm, formed by outgrowths from the Ascon tubes situated most
peripherally ; as a consequence the primitively wide and irregular en-
trances between the outermost tubes into the intercanal system become
reduced to small orifices termed pseudopores. Secondly, the intercanal
system may become greatly enlarged towards the centre of the sponge,
forming a false gastral cavity or pseudogaster. In consequence of these
modifications of the intercanal system the sponge may secondarily
assume the form of an Olynthus, well seen in the species Clathrina

ia. 66.

Canal system of Clathrina ventricosa, Crtr., seen in vertical section. psd, pseudoderm ; Ps.G,
pseudogaster ; osc, oscula ; i.c, intercanal system ; pp, pseudopores (7r.c. on the right, should be
t.c.). Schematised after Dendy.

ventricosa, Carter (Fig. 66). Here, however, the apparent pores are really
pseudopores (pp) leading into the intereanal system (?.c), and the apparent
gastral cavity is a pseudogaster (Ps.@), opening by a pseudosculum. The
true oscula (osc) open into the pseudogaster, and the wall of the vasiform
sponge is made up of the coiled Ascon tubes. A pseudoderm (psd) is
formed towards the cavity of the pseudogaster as well as towards the
exterior of the body wall. The two species Clathrina ventricosa and
tripodifera offer striking examples of homoplasy, since a very similar form

_ and structure is arrived at in perfectly different ways, and the large
central cloacae, with their excurrent orifices, are not in the least homo-
logous in the two forms.

96 SPONGES

The modifications of the canal system in the Leucosoleniidae are such
as are the direct result of the modifications of the external form which
have already been described. It has been shown that the sponge
may take on a bushy, arborescent, or creeping form (Figs. 3, 4, and
5). Since the canal system follows the external form in its arrange-
ment, and is therefore easily understood by simple inspection of the
sponge colony, it need not be further considered here.

(b) The Canal System of the Heterocoela—In the calcareous sponges
characterised by a discontinuous distribution of the gastral layer
and its restriction to the flagellated chambers, the canal system
may be of the second or third type, ie. without or with a
system of excurrent canals interpolated between the chambers and
the gastral cavity (see above, p. 32). The sub-order Heterocoela
comprises all the forms which were classified by Haeckel under
the two families Sycons and Leucons, the former having a
canal system of the second, the latter of the third type. The
grouping of the genera of Heterocoela by characters of the canal
system hardly corresponds with their natural affinities, but it
is convenient to consider the canal system under its two grades,
which we may term the syconoid and leuconoid types respectively.
The best examples of the former are seen in the genus Sycon, and
of the latter in the genus Leucandra.

The simplest syconoid type arises from the Olynthus by the
formation of hollow diverticula of the gastral cavity, just as in
Leucosolenia. The transitory homocoelous condition represented by
the young sponge at this stage is, however, soon passed over.
Ingrowths of the dermal layer into the gastral cavity take place
between the diverticula (Maas, 1898), and as a result of this invasion,
comparable to the similar ingrowths which in Ascons form the endo-
gastral networks frequently present (see above, p. 48), the gastral
layer becomes broken up and discontinuous, and confined to the
diverticula or radial tubes, while the general gastral cavity becomes
lined by a flat epithelium derived from the ingrowing dermal layer.
The sponge has now reached the heterocoelous grade of structure,
but even in the adult the upper portion of the oscular tube is often
found lined by a continuous layer of collar cells which extend from
the uppermost ciliated chamber to the commencement of the oscular
rim, and represent a remnant of the primitively continuous gastral
layer of the Olynthus. The ciliated chambers have received in
Sycons the special name of radial tubes, and they differ further from
the diverticula of Leucosolenia in that they remain relatively short,
‘soon attaining their limit of growth, while those of Leucosolenia, as
we have seen, continue their growth indefinitely and ultimately
give rise to new oscula. Between the radial tubes spaces are
enclosed on the exterior of the sponge which are perfectly com-
parable in every way to the intercanal system of Ascons, but

es

which are now better distinguished as the incurrent or inhalant
system.

The further development of the syconoid type takes place chiefly
by a narrowing of the

SPONGES 97

primitively wide incurrent ial 3
spaces between the radial ; me EES
tubes, which become closed (pee
in to form definite incurrent ee a ne aR
canals. In the simplest eae CSS DESERET SETTSOTTS oon GC.
ease (Fig. 67) a dermal ost -" in.c pas
membrane is formed by frase paoeomwereneceoen
outgrowths from the ex- ee ¥
tremities of the radial \\ SDocrnereerweremergetite.
tubes, in exactly the same : Hes
way as in the formation Fic. 67.
of a pseudoderm in Ascons, Section of the body wall of Sycon ge latinosum. The
external surface is to the left, the internal surface to
and the entrance to the the right. in.c, incurrent canal; pr.p, prosopyle ; r.t,

radial tube (flagellated chamber); app, apopyle; ost,

incurrent space 1S thus ostium ; G.C, gastral cavity.

narrowed to a circular

aperture, the dermal pore or ostium (ost), comparable to a pseudo-
pore of Clathrina ventricosa. The incurrent space becomes further
reduced by coalescence taking place between adjacent radial
tubes where they come into contact, thus interposing partitions, as
it were, which divide up the continuous incurrent space. Finally,
in many forms the dermal layer at the distal extremities of the
radial tubes becomes thickened to form a cortex, through which the
harrow incurrent canals pass to reach the radial tubes (Figs. 68,
69). These changes, and especially the formation of a cortex, have
the effect of completely masking the folded and lobed appearance
of the body wall, which results from the outgrowth of the radial
tubes, and the outer surface of the body presents a smooth, porous
surface, so that the form and appearance of the Olynthus may be
perfectly retained (Figs. 9, 10).

In addition to these changes in the incurrent system, various
modifications may take place in the radial tubes, or in their relations
to the gastral cavity. In the first place, the radial tubes may become
very much branched and secondarily complicated. A more im-
portant change, however, from the morphological point of view, is
the formation of an excurrent duct connecting the radial tube with
the gastral cavity—that is to say, the flagellated chamber is, as it
were, carried outwards, and does not open into the gastral cavity
directly, but communicates with it by means of a short duct lined
by flattened epithelium. At the same time the excurrent aperture,
or apopyle, of the chambers may become greatly contracted, appear-
ing as a perforation in a diaphragm separating the chamber from
its excurrent duct (cf. Fig. 67).

98 SPONGES

eel

=

'
-

Fic. 68.

Heteropegma nodusgordii, Pol., part of a transverse section. The external surface is upper- |
most; the gastral surface towards the lower side; the spicules are represented by straight
continuous lines ; the flat epithelium by dotted lines ; the collar cells by numerous small circles
rendering the branching radial tubes dark. (After Poléjaeff, Challenger Reports.) *x 50.

The leuconoid type of canal system has probably been evolved
from the syconoid type in more ways than one. There are at least
two modes of evolution which can be indicated with tolerable

Fia. 69.

Ute argentea, Pol., part of a transverse section. The concentric circles indicate transverse
sections of spicules, lying within the cortex. For other points see description of last figure.
(After Poléjaeff, Challenger Reports.) 100.

SPONGES 99

certainty. First, in some species of the genus Lewcilla we find
elongated chambers opening several together into short excurrent
canals formed by folding or evagination of the whole wall of the
gastral cavity (Fig. 70; cf. Fig. 44, 4). Secondly, in other cases the
excurrent system owes its origin to the further complication of ex-
current chamber ducts such as have been described above in the
syconoid type. Thus in Leucandra aspera (Fig. 71) a section of
the wall of an oscular tube shows the flagellated chambers close to
the margin of the osculum opening either directly or by means of
an excurrent duct into the gastral cavity. Further down two
or more chambers open by a common duct, which may now be
termed an excurrent canal. This condition may be due either

Fia. 70.

Teucilla connexiva, Pol., part of a transverse section. 2, excurrent canals ; for other points
see description of Fig. 68. (After Poléjaeff, Challenger Reports.) X50.

to the confluence of excurrent ducts primitively distinct, or to the
multiplication of the chambers by division. The further removed
any spot is from the oscular margin, the more the excurrent
system becomes complicated, until a canal system of a typical
leuconoid kind is produced. The excurrent canals may branch
frequently, and the incurrent system is correspondingly com-
plicated. The chambers, though varying greatly in size and
shape, are for the most part small and rounded in form, and
open directly into the wide excurrent canals. The canal system
when fully developed is thus seen to be of the eurypylous third
type. Aphodal and diplodal canal systems are not known amongst
Calearea. A leuconoid type, such as is seen in Leucandra aspera,
is the highest development of the canal system in this group.

100 SPONGES .-

In the above account of the canal system of the Heterocoela, a
Leucosolenia-like form, consisting of an Olynthus surrounded by numerous
radial diverticula, has been taken as the starting-point, and this pro-

Vertical section of the osculum of
Lewoandra aspera, schematised ; the thick
black lines represent the gastral layer,
the dotted lines the dermal layer. sp,
eseular sphincter ; sp, peristomial fringe
of spicules; ost, astia; G.C, gastral
cavity; ta.c, Incurrent canal; ec, ex-
current canal. Combined from several
sections.

|

]
ceeding is the more justified, since the |
majority of Heterocoela, and especially —
the genera Sycon and Leucandra, and
their allies resemble the Leucosolent-
idae in just those characters of skeleton,
histology, and embryology in which the
latter differ from Clathrinidae. There
may be, however, amongst the Hetero-
eoela forms which are to be referred
back to a Clathrinid ancestor which
has undergone modifications of the canal
system more or less parallel to those
which have been followed out above,
and though the Heterocoela have not
yet been studied from this point of
view it is highly probable that this is
the case. The genus Ascandra among
Clathrinidae, with its folded gastral
layer, represents a type of structure
which might easily serve as the starting-
point for the evolution of a hetero-
coelous canal system. The curious

genus Heteropegma of Poléjaeff (1883),

for instance, which in its outer form
closely resembles a typical Clathrina,
composed of a network of tubes, seems
to be modified from a Clathrinid
ancestor.

oe

Skeleton.—In the class Calcarea
the skeleton is composed of spicules
of carbonate of lime in the form of
calcite. The skeletal elements are
typically quite separate one from
another, but if united into a con-
tinuous framework, as is known to
occur in at least one instance (Petre-

i Alama ga fo

stroma), the union is brought about by fusion taking place between
the spicules themselves, and not by means of spongin or any other
form of special cementing substance. No distinction can be drawn
in this group between megascleres (skeletal spicules) and micro-

scleres (flesh spicules).

The caleareous spicules have a crystalline structure, and each
spicule, whatever its form, behaves optically as a single crystal
individual. Each spicule ray has an organic axial thread, and is

i

enveloped in an organic sheath, easily seen when the spicule is dis-
solved by acid. The mineral substance composing the spicule is
almost pure calcite, with traces of sodium, magnesium, and sulphates
(Ebner).

Forms of Calcareous Spicules—Three types of spicule occur in
calcareous sponges, the entire skeleton being composed of one or
more of these types in varying combinations, namely: (a) monaxon
(“acerate” or “oxeote”) spicules, of the form of a simple rod or
needle ; ()) triactinal or triradiate spicules, each with three arms
radiating from a centre; and (c) tetractinal or quadriradiate, con-
sisting each of four rays. Of these three types of spicule, the
second and third must be classed together, both being often con-
sidered as belonging to the tetraxon type ; the triradiates, however,
represent the more primitive form, to which, in the case of the
quadriradiates, an additional ray has been tacked on. Each quadri-
radiate consists of a basal system of three rays, similar in all
respects to a triradiate system, and of a fourth, “apical” or “ gastral”
ray. Hence the term triradiate system may be employed to denote
either a triradiate spicule or the three basal rays of a quadriradiate.
In considering, therefore, the modifications and variations of the
caleareous spicules, the most natural course will be to discuss first

the monaxons, then the triradiate systems, and lastly, the gastral
rays of the quadriradiates.

(2) The monaxon spicules vary very greatly in size. They are
sometimes straight (Fig. 72,7), but more often curved (Fig. 72, 7, ¢, 8),
and always have the two ends unlike.

(b) The triradiate systems exhibit modifications of considerable
morphological and systematic importance. At the outset it should
be remarked that they always lie embedded in the gelatinous tissue
of the body wall, with the rays directed more or less tangentially ;
and since the sponge surfaces are usually curved, the three rays
very rarely lie exactly in the same plane, and are often very strongly
bent out of it (Fig. 72, a). Hence, in the following discussion
of the numerous modifications of form exhibited by the triradiate
systems, each will be considered as seen projected in a plane tan-
gential to the body wall at the centre of the spicule.

The triradiate systems may be quite asymmetrical in form
(Fig. 72, p), but they more usually conform to some definite and
symmetrical pattern. In the latter case they may be either
“reoular” or “sagittal.” Regular systems consist of three similar
rays of equal size meeting at equal angles, so that the spicule is
symmetrical about three planes (Fig. 72, »). In sagittal systems,
on the other hand, there is but one plane of symmetry, and the
spicule exhibits a bilaterally symmetrical form, with two paired
lateral rays and an unpaired posterior ray (basal ray, Haeckel). The
sagittal form may, however, be produced in one of two ways, which

SPONGES IOI

102 SPONGES

should be carefully distinguished. In the first place, the angles
between the rays may be equal, and the bilateral form is the result
of hypertrophy or diminution of one ray (Fig. 72, c,d). In the
second place, the angles may vary as well as the rays, there being
two lateral paired angles and an anterior unpaired one (Fig. 72,
j, 1,n, 0). Ina natural classification of the triradiate systems, the
equiangular sagittal spicules should be classed with the regular
forms, and separated from those which are sagittal through varia-
tions in the angles. For the latter type Bidder has proposed the

Fic. 72.

Spicules of calcareous sponges. To the left (a-i) spicules of Clathrinidae ; to the right (j-s)
of Leucosoleniidae and Heterocoela. a and b, triradiates of Clathrina cerebrum, in profile view
and surface view respectively ; c, sagittal triradiate of Cl. blanca ; d, of Cl. lacunosa ; e, f, quadri-
radiates of Cl. cerebrum, with spiny gastral rays; g, “tripod” of Cl. cerebrum; h, diactine of
Cl. lacunosa ; 4, monaxon of Ascandra falcata ; j, triradiate, and k, quadriradiate, of Leucosolenia
variabilis ; l, triradiate of Lelapia australis ; m, quadriradiate of Leucosolenia complicata ; n, tri-
radiate of Leucetta pandora ; o, tuning fork” of Lelapia australis ; p, asymmetrical triradiate
of Leucosolenia variabilis ; q, monaxon of the same; r ands, two kinds of monaxons, one small
and straight, one large and curved, from Leucosolenia complicata.

useful term alate spicules, since their rays can usually be distinguished
by their form as well as by their inclination ; the posterior ray being
as a rule straight, the lateral rays more or less curved, like wings
on each side.

(c) Any of the numerous form varieties of the triradiate system,
symmetrical or asymmetrical, regular or sagittal, may become pro-
vided with an adventitious gastral ray, and so become a quadri-
radiate spicule. The gastral rays vary greatly in length, and may
be smooth or beset with small spines (Fig. 72, e, f,k,m). They
may further be straight or curved, the former being usually associ-

4

ated with equiangular triradiate systems, the latter with systems
which have the angles sagittal, and the curvature is then in the
plane of symmetry, being so directed that the tip of the gastral ray
points in the opposite direction to the posterior ray. All the
numerous variations of the gastral rays are quite independent of
the variations in the rays of the basal triradiate system.

Arrangement of the Spicules in the Skeleton.—The. simplest types
of skeleton are seen in the Olynthus stage (Figs. 1 and 60, /), which
furnishes a natural and convenient starting-point for tracing the
evolution of the skeleton. However complicated the structure of
the adult sponges, in the Olynthus stage they differ from one
another, as has been said, by characters merely of specific value,
the arrangement and relations of the spicules being of a uniform
character.

In the Olynthus the spicules form a single layer supporting and
protecting the thin body wall. The monaxons are placed more or
less tangentially with one end embedded in the tissues, and the
other extremity projecting freely on the exterior of the sponge; a
situation which explains the difference between the two ends of
these spicules (Fig. 60, /). The triradiates, on the other hand, are
completely embedded in the body wall, and are so placed that one ray
of each triradiate points downwards, away from the osculum, while
the other two slant obliquely upwards and outwards to the right
and left. In this way an unpaired posterior ray is marked off from
two paired lateral rays; but the distinction between them may be

- one which is only recognisable when the spicules are im situ in the
sponge wall (regular triradiates, Figs. 1 and 42), or the spicule may,
on the other hand, exhibit a structural differentiation of the rays,
correlated with their position and function in the sponge (sagittal
triradiates, Fig. 60, 2). What has been said of the triradiates
applies also to the three basal rays of the quadriradiates, which
have an exactly similar orientation; the fourth ray, on the other
hand, projects freely into the gastral cavity on the inner side of
the body wall, never towards the exterior. If the gastral rays are
curved, they always point up towards the osculum.

From the skeleton of the Olynthus may be derived that of any
adult calcareous sponge by a series of adaptations to the structural
requirements of the various parts added during growth.

In the Homocoela the skeleton retains in all parts of the body
the primitive arrangement in a single layer, seen in the Olynthus,
but exhibits marked differences in the two families of the sub-order.

SPONGES 103

The family Clathrinidae is characterised by equiangular triradiate
systems, a type of spicule doubtless correlated with the reticular form and
growth of the sponges themselves (cf. p. 7 supra) Monaxons may be
present and some of the triradiates may develop gastral rays, but in

q

104 SPONGES

the more primitive forms the whole skeleton is made up of tri-
radiates alone. The primitive orientation of the triradiates, found in
the Olynthus, is only retained, as a rule, in the region of the oscular
tube, while in the tubar system generally the arrangement becomes
confused so that posterior and lateral rays cannot be distinguished by
their position. In some forms, however, characterised by a more erect
growth, such as Cl. blanca and lacunosa (Fig. 8), the posterior ray is in-
dicated by its greater size, so that the triradiates become sagittal, while
remaining equiangular (Fig. 72, c). In lacunosa this feature is carried to
an extreme in the stalk, where a distinct peduncular skeleton is developed,
composed partly of sagittal triradiates (Fig. 72, d), partly of diactinal
monaxons, 7.¢. reduced triradiates (Fig. 72, h). Some species of Clathrina
have triradiates of special form on the exterior of the body, as an instance
of which may be mentioned the “tripods” of Cl. cerebrum (Fig. 72, 9).
In forms with a distinct pseudoderm this membrane may be supported
by a layer of special spicules forming a dermal crust.

In the Leucosoleniidae the triradiate systems, if symmetrical, are
always sagittal—that is to say, alate forms, with paired angles and
well-marked posterior and lateral rays (Fig. 72, j, k, 1). Monaxons are
always present in the species of this family (Fig. 72, q,s). The
sagittal form of the triradiates is correlated with the more erect growth
of these forms, and the spicules in question have a constant orientation
with regard to the canal system—that is to say, they tend to be so placed
that the unpaired posterior ray points in the opposite direction to the
course of the water-current. Hence in the oscular tubes the posterior rays
point, as in the Olynthus, towards the base, while in the diverticula the
triradiates become arranged with their posterior rays pointing towards
the blind apex (Fig. 73), and the same arrangement is repeated in the
secondary and tertiary diverticula formed by branching, so long as they do
not exceed a certain length. In this way the diverticula, though arising
as simple folds of the wall of the oscular tube or Olynthus, acquire a
special skeleton of their own, distinct
from that of the oscular tube in its
arrangement, though not as regards
the spicules composing it. When the
diverticula have grown to a certain
length, however, they give rise to new
oscula which are formed by perforation
of their blind extremities. Where a
new osculum is about to be formed,
the arrangement of the triradiates
which are formed at the growing ex-
tremity of the diverticulum first be-.

I gute be _ comes confused, and then reversed,

a Diagranotadiverticulum ofZevowlenia: go that in the terminal portion the
triradiates in the oscular tube (osc.t.) and unpaired rays point away from the
in the diverticulum (div.). The arrow er < s
points towards the oscular opening. apex instead of towards it. In this
way the arrangement proper to an

oscular tube is acquired precociously, at a time when the physiological

SPONGES 105

conditions that prevail are the exact opposite of those with which the
arrangement of the spicules is usually correlated.

The arrangement of the spicules in the diverticula and oscular
tubes of Leucosolenia (Fig. 73) foreshadows, and gives a clue to,
the plan of the skeleton in the Heterocoela. Taking the simpler
syconoid type as the starting-point for this group, we find that at
their first origin the ciliated chambers or radial tubes arise as
simple diverticula of the gastral cavity, differing only from those
of Leucosolenia in that they are more numerous and retain a more
simple unbranched condition, not giving rise to new oscula. Each
radial tube has its wall supported by spicules forming a special
tubar skeleton, distinct as a rule from the more internal gastral
skeleton both inarrangement and composition, and representing, there-
fore, in the latter respect a slight advance in specialisation upon the
state of things seen in Leucosolenia. In the more primitive types the
organisation scarcely advances beyond this point, except for the
formation round the osculum of a special peristomial skeleton, con-
sisting for the most part of elongated monaxons, and of a peduncular
skeleton in the stalk. But with fusion between the distal ends
of the radial tubes, to form a cortex, a special skeleton becomes
differentiated in this region also, so that the skeleton of the body
wall in a typical Sycon consists of three layers: (1) most externally
a cortical skeleton, which is said to be “smooth,” when it consists
of triradiates only, and “hispid,” when it contains monaxons, with
or without triradiates ; (2) a tubar skeleton composed of triradiate
systems, some of which may develop a gastral ray; (3) most
internally a gastral skeleton, composed mainly of quadriradiates
(Figs. 68, 69).

The tubar skeleton shows two distinct types of organisation
known respectively as the articulated and the non-articulated. In the
former, which is the more primitive, and directly comparable to the
state of things in Leucosolenia, each radial tube has its wall supported
by sagittal triradiate systems arranged in several series, each with
the unpaired posterior rays pointing towards the distal extremity of
the chamber (cf. Figs. 74, a, and 73). In the non-articulated type
of tubar skeleton there is but a single series of these triradiates,
each one situated near the base of the radial tube and sending a
greatly elongated posterior ray towards the apex, which meets, and
runs parallel to, a similarly hypertrophied Jateral ray (Poléjaeff) of
a triradiate of the cortical skeleton (Fig. 74, d). By interlocking of
these two systems of modified spicule rays the chamber acquires a
firm and rigid skeleton.

With the evolution of a leuconoid type of canal system the
pronounced radial structure seen in the Sycons becomes lost, and
the elongated radial tubes become very much shortened and con-

7

106 SPONGES

verted into the smaller spherical ciliated chambers of the third type
of canal system. As a consequence the regular tubar skeleton
disappears and is replaced by an irregular parenchymal skeleton
supporting the chambers and canal system and making up the
greater part of the thick body wall, between the cortical and
gastral layers of the skeleton.

One family of Heterocoela deserves special mention, however, as
regards its skeleton, namely the Pharetronidae. The anatomical structure
of this family is very imperfectly known, since most of its members are
fossil, and therefore cannot be studied at all with respect to their canal
system, while in many cases even the hard parts are very unsatisfactorily
preserved and the finer details impossible to make out. Two living

Fic. 74.

» ‘Types;:of tubar skeleton in Sycons. a, articulate type; }, inarticulate type. (After
Haeckel.)

species are known—Lelapia australis, Gray, from the coast of Victoria ;
and the remarkable Petrostroma schulzei, Dod., from Japan. From a
comparison of the living and extinct forms, the Pharetronidae would
appear to be Heterocoela, with a leuconoid type of canal system and
with a skeleton of more or less pronounced fibrous structure. The fibres
in typical cases are composed wholly or in part of interlocking spicules
of a peculiar type, in shape like a tuning-fork (Fig. 72, 0). The
spicules in question are simply entangled to produce the fibres, and are
not held together by any special cementing substance. In Lelapia and
Petrostroma the fibres are made up entirely of tuning-forks, but in many
fossil forms, as Sestrostomella, they contain an axis or core of much larger
and stouter triradiates, and other spicules may enter into their composi-
tion. In Lelapia and the fossil forms the fibres ramify through the
whole parenchyma, starting from the gastral skeleton and taking an
irregular course towards the cortex, so as to produce an anastomosing net-

SPONGES 107

work. In Petrostroma, however, the fibres are entirely confined to a
relatively thin outer “covering layer,” which perhaps represents more
than the cortex ; and the greater portion of the sponge body is occupied
by a continuous skeleton framework made up of quadriradiates fused

‘together by secondary deposits of calcite ; a type of skeleton not known

to occur in any other calcareous sponge, recent or fossil.

Phylogeny of Calcwreous Spicules—The triradiates with sagittal angles
occurring in Leucosolenia and the greater number of Heterocoela are
spicules morphologically of a different type from the equiangular
triradiates of Clathrinidae and a few LHeterocoela. In the Clathrinidae
the triradiates are the first spicules to appear, and each is shown by
the development to be formed by fusion of three monaxons, a fourth
being added in the case of quadriradiates. When independent monaxons
oceur in this family, they would appear to owe their origin entirely to
modification of triradiates (secondary monaxons). In Leucosoleniidae, on
the other hand, the first spicules to appear are true (primary) monaxons,
each secreted by a single cell. The triradiates in this family appear
later than the monaxons, and the posterior ray develops at first much
more rapidly than the lateral rays.

In the Heterocoela the origin of the spicules is less known, but
has been studied in Sycon by Maas. The greater number of
Heterocoela resemble the Leucosoleniidae more closely than the Clathrinidae
in both skeleton and canal system.

Histology.—The description given above of the structure of the
Olynthus may be taken as representing the main traits in the histology
of the Calcarea generally. It is not necessary to do more here than to
describe the development of the three-rayed and four-rayed spicules of
Clathrinidae, interesting as instances of compound spicular systems derived
from more than one mother cell. Each ray has its own scleroblast, or
actinoblast, as it may be termed.

To form a triradiate spicule three cells migrate into the parenchyma
from the dermal epithelium and become arranged in a trefoil-like figure
(Fig. 75, 1). The nucleus of each cell then divides into two, in such a
way that one nucleus is placed more deeply and one more superficially.
Between each pair of sister nuclei a minute spicule ray appears, the three
rays being at first distinct from each other, but soon becoming united at
the centre of the system (Fig. 75, 2). As the rays grow in length the
protoplasm of each actinoblast becomes aggregated round each of the two
contained nuclei, and finally more or less completely segmented off to form
two formative cells, of which the one placed more internally travels to the
tip of the spicule ray, while the other remains at the base (Fig. 42, Bb,
bf.c). The apical formative cell (ap.f.c) sooner or later disappears, return-
ing, apparently, to the epithelium. The basal formative cell (b.fc) remains
at the base of the ray (Figs. 42, B, and 75, 3) until this portion is secreted
to its full thickness. It then migrates slowly outwards along the ray, and
in the fully formed spicule is found adherent to the extreme tip (Fig.
42, B, spc). In the formation of a quadriradiate spicule in the
Clathrinidae, the three basal rays are formed exactly as has been described
for the triradiates. Each quadriradiate spicule represents, in fact, a

10

|

108 SPONGES ‘

triradiate to which an adventitious gastral ray has been added. It is
remarkable that this fourth ray is derived from a distinct source from the
other three, its scleroblast, or gastral actinoblast, as it may be termed, being
derived from a porocyte at a comparatively late period in the growth of
the basal system, After the three basal rays have reached a certain
length, the nucleus of a neighbouring porocyte divides, and a portion of
the cell, with one of the nuclei, becomes constricted off, grows out towards
the minute triradiate, takes up a position over it—.e. internal to it—and
secretes a minute spicule ray which becomes fused and tacked on to the
basal triradiate system (Fig. 75, 4). The secretion of the gastral ray
may commence before its actinoblast is completely separated from the
porocyte. In the further development the nucleus of the gastral actino-
blast may remain single or divide into two or four nuclei, according to
the size of the ray to be formed. In all cases, however, the protoplasm

Development of equiangular triradiates and quadriradiates in Clathrina. 1, trio of actino-
blasts ; 2, sextet, with young spicule ; 3, late stage in the growth of the spicule, after loss of
the apical formative cells ; 4, division of a porocyte to form a gastral actinoblast ; 5, late stage
in the secretion of the gastral ray. ¢tr.syst, triradiate system ; bif.c, basal formative cell; g.act,
gastral actinoblast ; g.ray, gastral ray ; p, dermal aperture of pore.

of the actinoblast remains undivided, and covers at first the whole ray
(Fig. 75, 5), but later only its tip, in the form of a granular plas-
modium, very different in appearance from the formative cells of the
basal system which, at first granular, soon become very clear and free
from conspicuous granulations.

It is evident from their development that the many-rayed spicules of
Clathrinidae, and probably of all Calcarea, are compound spicules, repre-
senting a spicular system derived from fusion of primitively distinct
monaxons. Even the apparently monaxon spicules, always of large size
in this family, seem to be derived from a modification of the compound
triradiate type. In the Leucosoleniidae, on the other hand, the monaxon
spicules are always true primary monaxons, derived each from a single
mother-cell, and are the first spicules to arise in the development. The
triradiate systems of Leucosolenia are formed just as in Clathrina, from

_— .

SPONGES 109

three mother-cells, each of which divides into a basal and an apical
formative cell, but the unpaired ray at first greatly outstrips the other
two in its growth.

Classification.—The earliest general classification of the Calcarea was
that of Haeckel [7], who divided them by characters of the canal
system into Ascons, Sycons, and Leucons. Each of these groups was
further classified into seven genera, each genus being characterised by a
skeleton made up of one of the seven possible combinations of the three
types of spicules.

The threefold division proposed by Haeckel has generally been super-
seded by the binary classification of Polejaeff [18], who divided the entire
group into Homocoela, with the gastral layer continuous, and Heterocoela,
with the gastral layer discontinuous. The former group comprises
Haeckel’s Ascons, the latter his two remaining groups.

There can be little doubt that Polejaefi’s two groups do not represent a
natural classification of the group, but only two grades of structure. His
classification is, in short, a horizontal cleavage of the phylogenetic tree,
not a vertical one. It is highly probable that the Heterocoela are a
polyphyletic group, derived from more than one stock of Homo-
coela.

Amongst the Homocoela we have two very sharply defined families ;
on the one hand, the Clathrinidae with reticulate form, equiangular
triradiates, collar cells with basal nucleus, and parenchymula larva
(Ascetta line); on the other hand, the Leucosoleniidae with erect form, alate
triradiates, collar cells with apical nucleus, and amphiblastula larva (Ascyssa
line). The divergence between the two families of Ascons indicates the
deepest phylogenetic cleft in calcareous sponges. While the majority of
the Heterocoela approach the Leucosoleniidae, a few forms (e.g. Heteropegma)
certainly find their nearest allies among Clathrinidae. Hence a truly
natural classification of the Calcarea must proceed along these lines.
Nevertheless, any such classification, though to be looked for in the
future, seems to us premature and inconvenient at present. The
Heterocoela have not yet been studied in detail from this point of view,
and their phylogenetic connections are not yet sufficiently unravelled.
We cannot therefore adopt here for practical purposes the division of
Calcarea proposed by Bidder (1898) into the two groups—-Calcaronea
(Calcarea on the Ascyssa line) and Calcinea (Calearea on the Ascetta line).
We retain for the present the two groups of Poléjaeff, not as natural
orders, but as two grades of structure, indicating a frankly artificial
classification.

Rauff has recently proposed to divide the Calcarea into two divisions—
Dialytina, with spicules separate, and Lithonina, with spicules united into
a continuous framework (Petrostroma). This classification is obviously
unsuitable for the entire group, but may be usefully employed within
the limits of Pharetronidae, where we retain it.

As regards families, we adopt in the main the grouping proposed by

_ Dendy, but we are unable, in the first place, to retain his so-called
heterocoelous family Lewcascidae. The true position of the forms included
in this family is amongst the Clathrinidae. In the second place, we retain

.

110 SPONGES

as a natural family the Pharetronidae, which Dendy wishes to distribute
amongst the other Heterocoela.

Grave A. Homocog.a, Pol., s. Asconrs, H.

Famity 1. CiLatHrinmar, Minchin. Form reticulate. Triradiate
systems always present, equiangular ; monaxons present or absent. Collar
cells with nucleus at base. Larva a parenchymula. Genera—Clathrina,
Gray (= Ascetta, H., pars. Ascaltis, H., pars. ete, and Leucascus, D.) ;
Figs. 2, 6, 7, 8; Ascandra, H., emend. (= Homandra, Ldf., for Ascandra
falcata, H.) ; Dendya, Bidder, for Clathrina tripodifera, Crtr. Famity 2.
LEUCOSOLENIDAE, Minchin. Form erect; monaxons always present ;
triradiates, if present, alate; collar cells with nucleus apical; larva an
amphiblastula. Genera—Ascyssa, H.; Leucosolenia, Bwk. (= Ascandra, H.,
pars,, etc.) ; Figs. 3, 4, 5.

|
Gastral layer continuous. |

GRADE B. HETEROCOELA, Pol.

Gastral layer discontinuous and restricted to chambers. 7

Famity 3. Sycerrmar, D. Chambers elongated, radially arranged
round the central gastral cavity, their ends projecting on the dermal
surface, not covered by a dermal cortex. ‘Tubar skeleton articulate. _
Genera—Sycetta, H., emend. ; Sycon, Risso, emend. (Figs. 9, 10); Sy-
cantha, Ldf. Fairy 4. Grantipar, D. With a distinct and continuous
dermal cortex covering over the chamber layer, and pierced by inhalant
pores. No subdermal sagittal triradiates, nor conspicuous subgastral
quadriradiates, The flagellated chambers vary from elongate and radially
arranged to spherical and irregularly scattered ones. The skeleton of the
chamber layer varies from irregularly articulated to irregularly scattered.
Genera—Grantia, Fleming (Fig. 11); Ute, O.S.; Amphiute, Han. ; —
Utella, D.; Anamiczilla, Pol. ; Sycyssa, H.; Lewcandra, H. (incl. Polejna, Lat. ;
Vosmaeria, Ldaf.; and Teichonella, Crtr, Figs. 12 and 71); Eilhardia,
Pol. (Fig. 13) ; Leucyssa, H. ; Lamontia, Kirk. Fay 5. Hererorpmar,
D. A dermal cortex as in the last. Subdermal sagittal triradiates
present. Flagellated chambers as in the last. An articulated tubar_
skeleton may or may not be present. Genera—Grantessa, Ldf. ; Heteropia,
Crtr.; Vosmaeropsis, D. Famitry 6. AmpHoriscipar, D. A dermal
cortex as in the last. Conspicuous subdermal quadriradiates, with
inwardly directed apical rays, are present. Flagellated chambers as in
last. Genera — Heteropegma, Pol.; Amphoriscus, H.; Syculmis, H. ;_
Leucilla, H. (including Pericharax, Pol.) ; Sphenophorina, Breitf. Famry
7. 7PaHarerronipar, Z. Skeleton with fibres formed by interlocking _
of spicules. Sup-Famity 1. Dranytinag, Rff. With all spicules
separate. | Genera — Lelapia, Crtr.; *Diaplectia, Hinde [Ool.];
*Euplocalia, Steinm, [Tr.]; *EZudea, Lamx. [Tr. Jur]; *Colospongia, |

—

+ Fossil and recent.

SPONGES II!

Laube [Tr.] ; *Celyphia, Pom. [Tr.]; *Himatella, Z. [Tr.] ; *Peronidella,
Zeise (= Peronella, Z.) [Jur. Cret.]; *Elasmocoelia, Roem, ([Cret.] ;
*Conocoelia, Z. [Cret.]; *LEusiphonella, Z. [Jur.]; *Corynella, Z.
[Tr. Jur. Cret.]; *Myrmecium, Goldf. [Tr. Jur.]; *Jnobolia, Hinde
[Ool.]; *Lymnorea, Lamx. [Jur.]; *Stellispongia, dOrb. [Tr. Jur.] ;
*Trachysimia, Hinde [Jur.] ; *Sestrostomella, Z. [Jur. Cret.] ; *Blastinia, Z.
[Jur.] ; *Synopella, Z. [Cret.] ; *Oculispongia, From. [Jur, Cret.] ; *Crispi-
spongia, Qst. [Jur.] ; *Elasmostoma, From. [Jur. Cret.]; *Rhaphidonema,
Hinde (Cret.]; *Pharetrospongia, Soll. [Cret.] ; *Holcospongia, Hinde
[Ool.]; *Pachytilodia, Z. [Cret.]; *Rauffia, Zeise [Jur.]; *Luzittelia,
Zeise [Jur.]; *Strambergia, Zeise [Jur.] ; *Thalamopora, Roem. [Jur.] ;
(Polysteganinae, Rt.) ; *Verticillites, Detr. (= Tremacystia), [Cret.], (Fig.
14, A). Sops-Famity 2. Lirnonrnasn, Rff. With body spicules united
by fusion into a rigid framework; fibres confined to cortical layer.
Genus — Petrostroma, Déd. (Fig. 14, B).

Many of the fossil forms included here under Dialytinae will very
likely prove, when better known, to belong to the Lithoninae.

Incerti: sedis—* Protosycon, Z. [Jur.] ; (Sycettidae 2).

CLASS II. HEXACTINELLIDA.

The Hexactinellida or Triazonia are a group of sponges character-
ised in the first instance by the possession of siliceous spicules of the
triaxon type, which are therefore primitively six-rayed. This
fundamental structural peculiarity is correlated with a very uniform,
and at the same time a very characteristic type of organisation,
rendering the group one almost as sharply marked off from other
sponges as are the Calcarea.

To judge by the abundance of fossil remains, the Hexactinellids
seem to have been a very abundant group at all times. At the
present day they are almost confined to the deep sea, but in this
region they are a widespread, and apparently flourishing group.
It is to their peculiar habitat, however, that must be ascribed our
still very great ignorance with regard to many points, especially of
their histology and life-history.

1. Canal System.—The embryonic development of the Hexac-
tinellid sponges is not known; but very young specimens, still
without an osculum, have been described by Schulze in his
great monograph [21], from which it would appear that the
starting-point for the development of the canal system in these
forms is a stage which has advanced considerably beyond the
Olynthus condition, and conforms more to the second type of canal
system (Fig. 76; cf. Fig. 44), the gastral layer being folded to

* form flagellated chambers. The wall of the sponge even in these

* Fossil forms: Tr.=Trias, Jur.=Jurassic, Ool. =Oolite, Cret. = Cretaceous.

112 SPONGES

early stages consists of five layers (Figs. 76, 77): (1) an outer
porous skin, the dermal memlrane (d.m); (2) within this is a space
traversed in all directions by strands of tissue, which constitute
the subdermal trabecular layer (sd.tr) ; (3) within this is a continuous
layer of thimble-shaped flagellated chambers, the blind ends of
which are turned towards the dermal surface, and their openings
towards the gastral cavity (ji.c); (4) internal to the chambers is
another space, traversed by the subgastral layer of trabeculae (sq.tr),
quite similar in its structure and appearance to the subdermal

Fic. 76.

Longitudinal section of a young specimen of Lanuginella pupa, O.S., with commencing
formation of the oscular area. The spicules are omitted from the drawing. x35. (After F. B.
Schulze.) d.m, dermal membrane ; sd.tr, subdermal trabecular layer ; fl.c, flagellated chamber ;
sg.tr, subgastral trabecular layer ; g.m, gastral membrane ; G.C, gastral cavity ; ose, region of
future osculum.

layer; (5) and finally, the gastral cavity is limited by a porous
gastral membrane (g.m), which recalls in its structure the dermal
membrane. Of these five layers, the third comprises the whole
gastral layer; the first, second, fourth, and fifth are differentia-
tions of the dermal layer.

The five layers that have been described recur in the same order
and with similar characters in the body wall of all Hexactinellids,
which exhibit a remarkable uniformity in this respect. The
chief modifications that are met with in the canal system are due

|
.

SPONGES 113

either (a) to a folding of the chamber layer as a whole, or ()) to
the folding and branching of the individual chambers.

(a) The simplest cases of the folding of the chamber layer result
in a type of canal system which reminds us of what has been de-
scribed above in the calcareous sponge, genus Leucilla (ef. Figs. 70
and 78). Short excurrent bays are formed into which the chambers
open, the latter being disposed into radiating groups round each
bay. Further development of this process of folding leads to the
formation of long branched excurrent canals, and the whole canal
system approaches very nearly to the type seen in Leucons. The
extent to which the folding of the chamber layer affects the other

Fia. 7.

Section of the body wall of Euplectella aspergillum, Owen. X110. (After F. EB. Schulze.)
f.c, floricomes (i.e. a form of hexaster); pre, principalia; ast, parenchymal hexasters ; prp,
prosopyles ; app, apopyles. Other letters as in Fig. 76.

layers of the sponge varies considerably. In the simplest cases the
subdermal trabecular layer alone is affected (Fig. 78), and extends
down into the interspaces between the folds of the chamber layer.
In most cases, however, the subgastral trabecular layer is folded
with the chamber layer, so that it extends into the excurrent
canals, while the subgastral membrane remains unaffected, and
either stretches across the openings of the excurrent canals (Fig. 79),
or is interrupted at these spots. But in extreme cases, as seen in
the family Hyalonematidae, the subgastral membrane shares in the
folding of the chamber layer and forms a lining to all the excurrent
canals. In no case does the subdermal membrane take any share
in process of folding.

| ae |
114 SPONGES

meee:

Se

SOO.

ayes
9"

Pa

GC.

Deak

ape,

Fic. 78.

Section of the body wall of Bathydorus fimbriatus, F.E.S. The spicules are omitted from
the drawing. x30. (After F. E. Schulze.) ez.c, excurrent canals. Other letters as in Figs.

Fic. 79.
Section of the wall of Taegeria pulchra, F.E.S. The spicules are omitted. x20. (After F.

E. Schulze.) The letters as in the three preceding figures.

SPONGES 115

(b) The instances of the chambers themselves being folded or
branched are numerous, and an extreme case is seen in the ear-like
form Luryplegma (Fig. 20, C, and Fig. 80).

This condition is at first sight difficult to distinguish from the condi-
tion found in the Hyalonematidae, a family remarkable for the fact that
the chambers grouped round each excurrent canal are continuous with
one another at their apopyles, the gastral epithelium passing on without
interruption from chamber to chamber. In fact, each excurrent canal
in Hyalonema might be thought to be a single, branched chamber, were it
not for the important difference that the subgastral layer and the gastral
membrane extend, as has been said, into it. This feature at once dis-
tinguishes the excurrent sinuses from branched chambers, since no

am.

Fic. 80.

Section of the wall of Euryplegma auriculare, F.E.S. All spicules are omitted except the
dictyonalia. x25. (After F. E. Schulze.) dict, the dictyonal framework formed by union of
the principalia one to another.

such extension of the inner layers of the body wall into the lumen
of the chambers ever occurs. The condition found in the Hyalo-
nematidae would appear therefore to represent a fusion of chambers
primitively distinct, or more probably still a condition where the multi-
plication of chambers by fission has stopped short of completion.

The uniform and simple structure of the body wall in Hexactinellid
sponges makes it easy in these forms to determine in any specimen. the
relations of the gastral cavity, since the anatomy of the young forms (Fig.
76) shows clearly that the subgastral membrane, through which the water
passes after issuing from the apopyles and traversing the subgastral frame-
work, is its boundary. Hence any space which is limited by, or borders
upon, the subgastral membrane, must be morphologically the gastral
cavity. We have already described the series of form modifications
whereby the gastral cavity may become greatly widened, and finally, in

116 SPONGES

such a form as Caulophacus, becomes merged, as it were, in the outer
world. The converse series of changes, on the other hand, where, by a
process of folding, a portion of the outer world becomes enclosed to form
a pseudogaster or false gastral cavity, is not known (pace Lenden-
feld) to occur. The osculum of Hexactinellids is typically a wide
aperture, frequently partially closed by a delicate sieve-plate (Fig. 18).
In Euplectella and its allies (Figs, 15 and 18) parietal gaps, which have
no relation to the canal system, occur in the body wall, leading into
the gastral cavity.

. Skeleton.—The skeleton of the Hexactinellid sponges is of
Pa, interest from the morphological point of view, since the
spicules exhibit in remarkable manner the persistence of one funda-
mental type in the midst of infinite variations.

Forms of the Spicules—The primitive type of spicule in the
Hexactinellids is the regular hexactine, a form with six similar and
equal rays meeting at right angles at a common centre (Fig. 47, ¢).
Each ray is traversed by an axial organic thread, which after

= (M

Fic. 81.

Modifications of the triaxon type of spicule. a, sword-like hexactine ; b, c, two varieties of
the pinulus ; d, amphidisc; e, pentactine ; /, tetractine; g, rhabdus.

maceration becomes a minute canal. The six axial threads meet at a
point, forming the so-called azial cross, a structure of great importance
for determining the morphological centre of the spicule.

Spicules of this form are of common occurrence in most species
of the group. More commonly, however, the primitive hexactinal
form has become diversified by modifications, which may be grouped
into two series.

In the first place, one or more of the rays of the primitive
hexactine may vary in size relatively to the other rays, so as to
become either greatly hypertrophied, on the one hand, or reduced
even to the vanishing point, on the other hand. Unequal develop-
ment of the rays results in peculiar forms of the hexactine, such as the
sword-like hexactines, characteristic of the Huplectellidae (Fig. 81, a).
Complete atrophy, or rather arrested development, of one or more
of the rays, causes the primitively six-rayed type to become pent-
actinal, tetractinal, and so on, until finally only one or two rays
remain (Fig. 81, ¢, f, 7), and as the end term of this series we have
a simple monaxon rod, which may be either diactinal (rhabdus), or
monactinal (style). So long, however, as there are more rays than

SPONGES 117

one persisting, they always meet at a multiple of a right angle, and
the constancy of the angles between the rays at their origin is a
striking feature of the triaxon spicule, though often masked to
some extent by curvature of the rays themselves.

In the second place, one or more of the rays of the hexactine, or
of one of its reduced forms, may become modified in various ways ;
as, for instance, by becoming curved, or by the acquisition of spines,
knobs, hooks, and so forth, or finally, by the development of
secondary branches, which in their turn may be curved or orna-
mented in various ways. Specially noteworthy, and often of
systematic importance, are the various ways in which the rays, or
their secondary branches may terminate. Thus to take the hex-
actine as an example, its rays may end in sharp points (oxyhex-
actine), or in knobs (tylhexactine), or dises (discohexactine).

By the combination of modifications along different lines, there
results a great variety of forms of the triaxon spicule, some of which
have received special names and are characteristic of particular
families, or subdivisions of the group.

Fic. 82.

Characteristic Hexactinellid spicules. a, uncinate; b, clavula; c, scopula. (After F. E.
Schulze.)

As instances of such forms may be mentioned the pinuli (Fig. 81, 8, c),
spicules usually pentactinal, sometimes, however, hexactinal, in which
one ray directed radially, as regards the sponge body, and always pro-
jecting freely from a surface, either internally or externally, develops
numerous small spines, and resembles a fir tree; the various forms of
aster or rosette (hexaster), produced by branching of the rays, and giving
rise in their turn to a large series of varieties (oryhexaster, discohexaster,
“floricome,” “ plumicome,” etc., Fig. 48, 0, t, Fig. 77, f.c) ; the amphidiscs
(Fig. 81, d) characteristic of the Hyalonematidae, rhabdi which bear at
their distal extremities dise-like expansions curved towards the centre and
prolonged into several tooth-like protuberances ; the peculiarly ornamented
rhabdi known as wncinates (Fig. 82, a) and scopulae (Fig. 82, c), and the
monactinal clavulae (Fig. 82, b), and many other forms too numerous to
mention,

Many of the forms of the triaxon spicule depart widely in
appearance from the primitive type, and are often difficult to
recognise as belonging to it. In tracing the affinities of the
spicule, the axial canal affords in many instances a safe clue for
the detection both of those parts which are of secondary origin,
and those which have been lost, since, on the one hand, it is
not continued into the various spines or branches which may be

118 SPONGES —

developed on the primary ray, and, on the other hand, a minute
continuation of the axial thread may often be found indicating a
ray which has been completely lost. A beautiful instance of the
latter kind is seen in the diactines which have
the two rays placed in the same straight line
(secondary monaxons). In some instances the
four undeveloped rays are indicated by four
knobs, containing as many axial canals, which
form a minute axial cross at the morphological
centre of the spicule (Fig. 83, 4). In other
cases the four knobs are further reduced to a
slight swelling, or have disappeared altogether
(Fig. 83, B, C), the minute axial cross remaining,
however, to indicate the aborted rays. Finally,
even the axial cross may disappear, leaving no
trace of the missing rays.

A. C.

Fic. 88, The root tuft with which many Hexactinellids
Three stages in the re- AF@ provided is composed of long thread-like spicules,
duction of a hexactine which in Hyalonema may be two feet or more in
to the monaxon condi- : :
tion. In A four radi- length, and are furnished with recurved, anchor-
mentary rays are repre- ;1- | . : s4s
eetied Ey sont enniel like hooks at their distal extremities. Some of
in B there is only a these rooting spicules bear at their termination four
slight swelling in their - '
place; “iC they have hooks, placed at right angles to each other, and to
aps ieee gprs the shaft, and containing prolongations of the axial
e the lost rays F 5 “ “
are indicated by the canal; the spicule is therefore pentactinal, with one
minute axial cross in the
dxinl flament ton. ray very greatly developed. In others the anchor-
ing hooks are numerous and arranged according
to various types of symmetry ; they contain no axial canal, and are
therefore of secondary origin, but at some point in the shaft of the
spicule a minute axial cross can usually be found, proving it to be a
much elongated diactine. In a similar way the scopulae (Fig. 82, c) are
seen to be diactinal in their nature, the axial thread not being con-
tinued into the terminal branches.

Arrangement of the Spicules in the Skeleton.—According to their
position in the sponge body the spicules of Hexactinellids may be
divided into several categories, corresponding to the regions of the
body which it is their function to support or protect.

(1) Prostalia.—Defensive spicules, usually diactinal monaxons,
which project over the surface of the body, only found in Lyssacina.
A special differentiation of such spicules may form a protecting
fringe round the osculum, or an anchoring root tuft at the base
(prostalia marginalia et basalia). ‘Those scattered over the general
surface of the body are termed plewralia.

(2) Dermalia.—Spicules supporting the dermal membrane ;
usually hexactinal or pentactinal, with four similar rays lying em-
bedded in the membrane. They are distinguished as autodermalia,

SPONGES 119

or hypodermalia, according as their axial cross is placed within, or
beneath, the dermal membrane.

(3) Gastralia.—Spicules similar in form and function to the last
named, but supporting the gastral membrane.

(4) Parenchymalia.—Spicules supporting the general parenchyma
and the chambers between the dermal and gastral membranes. In
the most primitive types of skeleton, as seen in Holascus and Farrea,
the parenchymal skeleton consists of large regular hexactines
(principalia), arranged to correspond with the intervals between the
thimble-shaped chambers, two rays being disposed radially and four
tangentially (Fig. 77, prc). This primitive type of skeleton may
become much modified in various ways, both as regards arrange-
ment and composition, the primitive hexactinal principalia becoming
modified in form, and supplemented by other spicules (comitalia).
In the sub-order Dictyonina and in many Lyssacina the principal
spicules of the parenchyma are united into a continuous framework,
and distinguished as dictyonalia.

Union of the Spicules.—In many Hexactinellids the spicules re-
main separate from one another and simply interlock. In other
cases some of the spicules of the parenchyma become united to
form a continuous framework. This union is always effected by
secondary deposits of silica, never by spongin.

In the simplest method of union, characteristic of Dictyonina,
two parallel rays become apposed and united by concentric layers of
silica into a beam, in which the primitive component rays are dis-
tinguishable by their separate axial canals. In other cases the end
of a ray of one spicule becomes soldered to the central node, at
which the rays intersect, in another. In other cases again the rays
of adjoining spicules crossed in any direction are bound together
by web-like lamellae of silica. When two rays are not in contact,
cone-like elevations grow out from the sides of opposite rays, meet,
and finally fuse to form a connecting siliceous bridge or synapticula.
Since all these secondary deposits of cementing siliceous material
are without axial canals, they can easily be distinguished from the
true spicules. ;

In the Dictyonina the principal spicules of the parenchyma
become united early into a framework, and are separate only in the
growing portions of the sponge. Their union imposes a check on
the growth of the sponge in a lateral direction, but it can continue
to grow in length or at the free margin; hence the occurrence in
this group of tubular, plate-like, or cup-shaped sponges, the former
often very similar in form to those in the calcareous family Clath-
rinidae.

In the Lyssacina the spicules either remain separate (/yalo-
nematidae, Holascinae), in which case the sponge may attain to a huge
size (Poliopogon gigas, and others), or they may become united into

120 SPONGES

an irregular manner at a late stage in the life-history, setting a
limit to further growth.

General Remarks on the Skeleton.—Beautiful instances of adaptation to
the conditions of life in abyssal depths are seen in the arrangement of
the skeleton in sponges of this group. Thus in Luplectella the spicules
are arranged in fibres which run either longitudinally, or in transverse
circles, or diagonally, to form spirals running in two directions. The
longitudinal and transverse fibres strengthen the sponge to support the
weight imposed upon it by the continual shower of particles, skeletons of
Radiolaria, ete., raining down upon it from the surface. The spiral
fibres correspond to the lines of stress and strain produced in a cylinder
fixed at one end and free at the other, which is acted upon by a force at
right angles to its axis, and strengthens the sponge against the action of
currents. Some species of Euplectella are cornucopia-shaped and further
strengthened by lateral ridges (Fig. 15); such a form is adapted to
constant currents in one direction. Other species, adapted to currents in
any direction, are cylindrical and upright, and strengthened equally on
all sides (Keller, 1891).

In a brief but suggestive memoir Schulze [22] has drawn attention
to the remarkable fact that although the spicules of Hexactinellids are
composed, apparently, of non-crystalline material (colloid silica), yet their
axes possess the same symmetry as the crystals of the cubic system. Not
only is this true of the ordinary hexactine, but it is also seen in many of
the less common forms of spicule. Thus the discoctasters are spicules with
eight rays terminating in discs, each dise corresponding in position to one
of the eight corners of a cube ; again, in the nodes of the dictyonal frame-
work of many forms (e.g. Aulocystis), the twelve edges of the regular
octahedron are marked out by girder-like trabeculae; and the six
secondary planes of symmetry of the cubic system are often indicated by
branching of the hexactines, or by their hook-like curvature. These
facts invite a renewed investigation of the physical nature of the spicule
material ; should it prove beyond all doubt to be non-crystalline, then
these striking imitations of crystalline axes must be regarded as mechanical
adaptations in a supporting framework—the culmination, rather than the
starting-point, of the evolution.

3. IHistology.—The finer structure of the body wall is of very
uniform, and at the same time of very simple, composition. The
dermal membrane is covered by a flat epithelium, and the under-
lying parenchyma is composed as in other sponges of a matrix
containing collencytes, amoebocytes, and, doubtless, scleroblasts,
besides sperm masses and ova. A remarkable feature of the dermal
layer is its trabecular structure. Fine strands of tissue stretch
in every direction over a continuous lacunar space, furnishing a
very complete filtering apparatus for the ingoing water current. As
a consequence of this peculiar structure, the connective tissue system
is very greatly reduced in quantity, and in the trabeculae there
seems to be no sharp distinction between the epithelial and

SPONGES 121

parenchymal strata, a point in which Hexactinellids are perhaps
more primitive than other sponges.

The choanocytes, long unknown, have recently been discovered by
Schulze, who describes them in Schaudinnia arctica as a uniform layer of
columnar epithelium, each cell bearing a collar and flagellum. The body
of the cell is slightly constricted towards the middle, and expanded both
at its upper and lower ends. At the lower end the base of the cell forms
a foot-like plate, which contains the nucleus, and is in contact with the
similar basal plates of neighbouring cells to form a continuous protoplasmic
membrane, limiting the chamber towards the exterior and interrupted
only by the chamber pores or prosopyles, In surface view the basal
membrane shows a number of granular strands running from each nucleus
to its four neighbours, and so producing the appearance of a network or
lattice with approximately rectangular or rhombic meshes ; this is the
membrana reticularis formerly described by Schulze in the Challenger
material, and then but imperfectly understood. Finer strands, disposed
in an irregular manner, ramify in the meshes of the coarser network.
At their upper ends also the choanocytes are adherent to one another,
just below the origin of the collar, except where a prosopyle traverses the
chamber wall. In this way a continuous system of spaces is enclosed
between the narrowed middle portions of the cells. The collars are quite
separate from one another. The flagellum is connected with the basal
nucleus by an axial filament passing down through the body of the cell.

4, Development.— Nothing is known of the embryology. Schulze
found only immature ova, of the usual type, in the Challenger material,
and no larvae or even segmentation stages.

5. Classification.—The classification here adopted is that applied by
Schulze (1887) to recent forms, with a few subsequent additions or
emendations. In addition a certain number of fossil genera and families
have to be noticed, of which the exact position in Schulze’s system is
not in all cases clear and cannot be determined without special in-
vestigation.

Sus-Ciass 1. Lyssacrna, Z.

The spicules of the skeleton either remain separate or are united at
a late period of growth in an irregular manner by siliceous masses or by
transverse synapticulae,

OrprerR 1. Hexasterophora, F.E.S.

Hexasters always present in the parenchyma ; ciliated chambers
thimble-shaped, sharply separate from one another.

Famity 1. Evpiecre.yipar, Gray. The dermal skeleton contains
sword-shaped oxyhexactines with long proximal ray. (a) Sus-Famity 1.

1 Tn his most recent work on American Hexactinellids [24] Schulze abandons the
subdivisions Lyssacina and Dictyonina as a natural classification, and divides the
group into two orders: (1) Amphidiscophora, including the single family Wyalone-
matidae; and (2) Hexasterophora, which is extended to include not only the
remaining families of Lyssacina, but also all the Dictyonina.

122 SPONGES

EvUPLECTELLINAE, F.E.S. Tubular forms with transverse terminal sieve-
plate ; the body wall perforated by circular parietal gaps ; distal ray of
dermal oxyhexactine bearing a floricome. Genera—Euplectella, Owen
(Fig. 15); Regadrella, O.S. (Fig. 18). (6) Sup-Famity 2, HoLascrnag,
F.E.S. Tubular, without parietal gaps or superficially situated floricomes ;
with parenchymal oxyhexasters. Genera—Holascus, F.E.S. ; Malacosaccus,
F.E.S. (c) Sup-Famity 3. Tarcertnak, F.E.S. Sack-like or tubular,
the thin body wall perforated by parietal gaps of irregular size and
distribution. The skeletal lattice work of the body wall forms an
irregular meshwork ; with superficially situated floricomes. Taegeria,
F.ES. ; Walteria, FES. Genera incerti sedis—Habrodictyum, W. Th. ;
Eudictyum, Marshall ; Dictyocalyx, FES. ; Rhabdodictywm, O.S. ; Rhabdo-
plectella, O.S.; Hyalostylus, F.E.S. Famity 2. Hertwictpax, Tops.
(1892). Skeletal framework composed of hexactines and diactines united
by synapticulae; the free parenchymal spicules are hexactines of two
kinds, one confined to the surface ; characteristic hexaster, one with four
sickle-shaped hooks on each of the principal rays. Genera—Hertwigia,
O.S. ; Trachycaulus, FES. Famiry 3. ,AsconeMATIDAE, Gray (Schulze,
1897). Dermal and gastral skeleton containing pinuli with spined radial
rays projecting freely ; hypodermalia pentactinal, but no hypogastral
pentactines ; parenchymal discohexasters. | Genera—Asconema, Say.
Kent. (Fig. 17); Aulascus, F.E.S. ; Sympagella, O.S. ; Saccocalyx, F.ES. ;
7 Caulophacus, F.E.S. [Eoc.], (Fig. 20, C). Calycosoma, F.E.S.; Calycosaccus,
F.E.S. Famiy 4. tRossevirpag, F.E.S. (lijima, 1898). The dermalia
always without distal radial rays. (@) SuB-Famity 1. LEUCOPSACINAE,
lijima. Dermalia not differentiated into autodermalia and hypodermalia.
Genera— Leucopsacus, Iij.; Chauwnoplectella, Iij.; Placoplegma, F.E.S. ;
Aulocalyz, F.ES.; Euryplegma, F.ES. (Fig. 20, A) ; Caulocalyx, F.E.S. (6)
Sun-Famity 2. Lanueinecuinak, F.E.S. With distinct auto- and hypo-
dermalia; without octasters; plumicomes present; with or withont
oxyhexasters. Genera—Lanuginella, O.S. ; Lophocalyx, F.E.S. (= Poly-
lophus, F.E.S.) ; Mellonympha, F.E.S. (ce) Sus-Faminy 3. 7ROsSELLINAE,
F.E.S. With distinct auto- and hypo-dermalia; without octasters or
plumicomes ; oxyhexasters always present. Genera—Bathydorus, F.ES.;
Vitrollula, lij. ; tCrateromorpha, Gray [Eoc.]; Aulochone, F.E.S. ; Hyalascus.
lij. ; Rossella, Crtr. (Fig. 16) ; Aphorme, F.E.S.; Aulosaccus, lj. (d) Sus-
Famity4 @ AcantHascrnar, F.E.S. With distinct auto- and hypo-
dermalia ; octasters and oxyhexasters always present. Genera—Stauro-
calyptus, lij.; Rhabdocalyptus, lij.; Acanthascus, F.ES. ; Acanthosaccus,
F.ES.

[Rossellidae as yet undescribed; Schawlinnia, Trichasterina, and
Scyphidium, Schulze, 1899.]

Orper 2. Amphidiscophora, F.E.S.

Amphidises always present in the limiting membranes. No hexasters
in the parenchyma. Always with an anchoring root tuft. Ciliated
chambers irregular in shape, and not sharply marked off from one

another,
+ Fossil and recent.

-

Famity 5. ?tHyaLoneMaTIpAr, Gray (Schulze, 1893). Pentactinal
pinuli in both dermal and gastral membranes. (a) Sus-Famity 1.
THYALONEMATINAE, F.E.S. Genera—v7Hyalonema, Gray [Eoc.], (Fig. 19) ;
7Pheronema, Leidy [Eoc.] ; Poliopogon, W. Th. (Fig. 20, B); *Pyritonema,
Moy [Sil.]; *Oncosella, Rff. [Sil.]. (6) Sus-Famity 2. SEMPERELLINAY,
F.E.S. Genus—Semperella, Gray.

SPONGES 123

To these must be added the following families of extinct Lyssacina :—
Famity 6. *Prorosponarpak, Hinde (Rauff.1893). Genera—Protospongia,
Salter [Cambr.]; Phormosella, Hinde [Sil.]}. Faminy 7. *Dicryospon- /
@ipak, Rff. Genus—Dictyophyton, Hall [Sil. Dev.]. Famity 8. *PLEcro-
SPONGIADAE, Rff. Genera—Cyathophycus, Wale. [Sil.]; Palacosaccus,
Hinde [Ordov.]; Acanthodictya, Hinde [Sil.] ; Plectoderma, Hinde [Sil.].
Faminy 9. *Bracurosponerpak, Beecher. Genus—JBrachiospongia, Marsh
Sil]. Famity 10. *Parrersonrpar, Rff. Genus— Pattersonia, S. A.
Miller [Sil.]. Famrry 11. *Recepracu.itipak, Eichw. Genera—ZJschadites,
Murch. [Ordov. Sil.] ; Sphaerospongia, Peng. [Dev.] ; Receptaculites, Defr.
[Ordoy. Sil. Dev. Carb.]. Fammy 12. *AmpuHisponerpan, Rif. Genus
— Amphispongia, Salter [Sil]. Famiry 13. *Monaxipag, Marshall.
Genus— Stawractinella, Z. [Cret.]. Famiry 14. *Po~uakmar, Marshall.
Genera—Hyalostelia, Z. [Carb. Cret.]; Holasterella, Crtr. [Carb.] ; Spzr-
actinella, Hinde [Carb.] ; Acanthactinella, Hinde [Carb.].

Incerti sedis—* Astroconia, Soll. [Sil.]; *Teganium, Rff. [Sil.].

(Note.—Families 13 and 14 represent two groups, which, so far as
living forms are concerned, have been broken up and distributed amongst
other families, and it only remains for the fossil forms to- be similarly
treated.)

Sup-Cuass 2. Dicryonina, Z.

The large parenchymal hexactines are from the first united more or
less regularly as dictyonalia into a firm framework.

OrperR 1. Uncinataria, F.E.S.
With uncinates.

Sus-OrpeEr 1. Cuavoxaria, F.ES.

Groups of radially disposed clavulae in addition to pentactinal hypo-
dermalia and hypogastralia, sometimes also scopulue.

Faminy 1. Farrerpar, F.E.S. In the youngest portions of the tubes
the dictyonal framework consists solely of a single-layered network with
square meshes, each node of intersection bearing on either side a conical
boss projecting at right angles). Genera—JSarrea, Bwk. (Fig. 21) ; Clavis-
copulia, F.ES.

Sup-OrpEer 2. Scopunartra, F.E.S.

Groups of radially disposed scopulae in addition to pentactinal bypo-
dermalia and hypogastralia, never with clavulae.

* Fossil forms : Cambr. =Cambrian ; Ordov. = Ordovician ; Sil. = Silurian ; Dev. =

' Devonian ; Carb.=Carboniferous ; Eoc. = Eocene ; other references as under Calcarea

(above, footnote to p. 111): if the whole family is known only in the fossil condition,
the asterisk is not affixed to each separate genus.

It

124 SPONGES

Famity 2.7 Evretipar (Z.), F.E.S. Branched anastomosing tubes, form-
ing an irregular framework or the wall of a cup ; dictyonal framework of
the tubular wall always several layers, never, as in Farrea, a single-layered
network. Genera—LHurete, Crtr.; Periphragella, Marshall ; Lefroyella, W.
Th. ; *Tremadictyon, Z. [Jur.]; *Craticularia, Z. [Jur. Cret.] ; *Sphenaulaz,
Z. [Jur.]; *Sporadopyle, Z. [Jur.] ; * Verrucocoelia, Et.[Jur.] ; *Stawronema,
Soll. [Cret.] ; *Sestrodictyon, Hinde [Cret.]; *Calathiscus, Soll. [Ool.].
Faminy 3. 7MeEtuirrionipar, Z. Body in the form of a system of ramified
tubes or of a cup with lateral diverticula ; dictyonal framework with

irregular meshes; parietal skeleton honeycomb-like, with more or less’

hexagonal canals disposed radially ; each such canal occupied by an
extension of the chamber layer, and covered over externally by the
dermal, internally by the gastral membrane. No scopulae in gastral
skeleton. Genus—tAphrocallistes, Gray [Cret. Eoc.], (Fig. 22). Fammy 4.
7CoscinoporIDAk, Z. Body cup-shaped or plate-like, the wall traversed
by elongated, funnel-shaped, straight canals (incurrent and excurrent),
of which the wide openings, covered by the sieve-like limiting membrane,
are placed alternately on either surface of the wall, while the other
extremity ends in a blind point. Genera—*Coscinopora, Goldf. [Cret.] ;
* Leptophragma, Z. [Cret.]; *Pleurostoma, Roem. [Cret.] ; *Guettardia, Mich.
[Cret.]; Chonelasma,- F.E.S.; Bathyxiphus, FES. Famtty 5. Tre-

TODICTYIDAK, F.E.S. Incurrent and excurrent canals penetrate the body

wall with an oblique, longitudinal, or even curved course, not trans-
versely, Genera—Hezactinella, Crtr.; Cyrtaulon, F.E.S.; Fieldingia,
Sav. Kent. ; Sclerothamnus, Marshall.

OrpDER 2. Inermia, F.E.S.

Without uncinates or scopulae.

Famity 6. 7 MAEANDROSPONGIDAE, Z. The body consists of a con-
nected system of labyrinthine anastomosing tubes, between which there
is a connected interstitial system of interspaces. The water entering
by the latter passes through the walls of the tubes and along them
either into the gastral cavity or directly to the exterior. Genera—
Dactylocalyxz, Stutchb. ; Margaritella, O.S.; Scleroplegma, O.S.; Myliusia,
Gray ; Aulocystis, F.E.S.; *Plocoscyphia, Rss, [Cret.]; *Etheridgia, Tate

[Cret.] ; *Toulminia, Z. [Cret.] ; *Camerospongia, d’Orb. [Cret.]; *Cysti-

spongia, Roem, [Cret.].

To these must be added the following extinct families :—Famuty 7.
*STAURODERMIDAE, Z. (with sub-families PorospoNGINAE and STaurRo-
DERMINAE, Rff.), Genera—Cypellia, Pom. [Jur.] ; Stawroderma, Z. [Jur.] ;
Purisiphonia, Bwk, [Jur. Cret.] ; Porocypellia, Pom. [Jur.]; Casearia,
Qst. [Jur.]; Porospongia, d’Orb. [Jur.] ; Ophrystoma, Z. [Cret.] ; Cincli-
derma, Hinde [Cret.]; Eubrochus, Soll. [Cret.] ; Placotrema, Hinde
[Cret.]. Faminy 8. *CaLLopicryonrpar, Z. Genera—Callodictyon, Z.
[Cret.]; Marshallia, Z. [Cret.]; Porochonia, Hinde [Cret.]; Becksia, Schliit.
[Cret.] ; Plewrope, Z. [Cret.] ; Diplodictyum, Z. [Cret.] ; Sclerokalia, Hinde
[Cret.]. Famity 9. *Cortoprycuipar, Z. Genus—Coeloptychium, Goldf.

|

5

g

SPONGES 125

[Cret.]. Famry 10. *Venrricuritmasr, Hinde. Genera—Pachyteichisma,
Z. [Jur.]; Trochobolus, Z. [Jur.] ; Phlyctenium, Z. [Jur.] ; Ventriculites,
Mant. [Cret.], (Fig. 23); Schizorhabdus, Z. [Cret.]; Rhizopoterion, Z.
[Cret.] ; Sporadoscinia, Pom. [Cret.] ; Coeloscyphia, Tate [Cret. ]; Sestrocladia,
Hinde [Cret.]; Licmosinion, Pom. [Cret.]; Polyblastidiwm, Z. [Cret.] ;
Cephalites, T. Smith [Cret.].

CLASS III. DEMOSPONGIAE.

The sponges included in this class appear at first sight a very
heterogeneous collection. The variations of structure are very
great, and between the Demospongiae which stand furthest apart
in the scale—the Tetractinellids on the one hand, and the Keratosa
on the other—the differences are so pronounced that, if considered
by themselves, the former might be thought to have less in
common with the latter than with, for example, the Hexactinellids.
But even between extremes such as these, there is to be found a
complete series of intermediate forms, which is nowhere interrupted
by any such abrupt distinctions as those which mark off the Demo-
spongiae as a whole from the other siliceous sponges.

The Demospongiae represent, in fact, the class of sponges which
is the most widely spread, and most dominant at the present day,
comprising all the most familiar examples of the phylum Porifera.
Their cosmopolitan distribution places them amidst the most varied
conditions of existence, and they respond to the differences of their
environment by a wide range of adaptations. The Demospongiae
are at once the most plastic and the most highly organised of
sponges, as regards histological differentiation or elaboration of
anatomical structure. We find here the most perfect types of
canal system, and in such a form as Disyringa (Fig. 26), with
its single incurrent aperture, we find the extreme of individualisa-
tion seen in any sponge. On the other hand, those Demospongiae
inhabiting the shore-line tend to lose their individuality, and to
advance towards an impersonal condition, in which the primitive
individual becomes merely an ill-defined physiological centre in a
spreading and often amorphous growth.

Canal System.—The starting-point of the post-embryonic growth
and development in Demospongiae is a form known as the Lhagon,
which, like the Olynthus of Calcarea, represents a transitory stage
from which the existing forms of canal system in this group can be
derived by simple processes of growth. Hence the canal system
of the groups included under the designation Demospongiae —
the Tetractinellida, Monaxonida, Keratosa, etc.—are often known
as the Rhagon type of canal system.

The Rhagon (Figs. 61, ¢, and 84) is a little sponge organism, in

126 SPONGES

shape like a cake or bun, being usually slightly flattened and spread
out, with an irregular, but more or less circular outline. The upper
surface of the body is studded with minute pores (prosopyles),
leading directly into small rounded flagellated chambers, which in
their turn open by wide apopyles into a spacious gastral cavity,
lined everywhere by flattened epithelium. The water passes out
of the gastral cavity by the osculum, which is often raised up like
a chimney from the surface of the body. The lower surface of the
body is in contact with the surface of the object to which the
sponge is attached, and contains no chambers. Hence two regions
can be distinguished conveniently in the body wall ; a lower portion,
devoid of chambers or pores, the hypophare, and an upper portion,
containing all the chambers, the spongophare.

From the foregoing it will be seen that the Rhagon is con-
siderably in advance of the Olynthus as regards organisation, since
it has a canal system of the second type, with the gastral layer

Fic. 84.

Vertical section of a Rhagon, diagrammatic. o, osculum; p, gastral cavity. (After Keller,
X about 100).

confined to the flagellated chambers, and the gastral cavity lined
everywhere by flat epithelium of the dermal layer. No stage with
fully formed pores and osculum, and with a canal system in a state
of functional activity, is known to occur of a simpler type than the
Rhagon in any Demosponge, but a transitory embryonic stage is
often found which may be interpreted as a suppressed and con-
tracted Olynthus stage (Fig. 63, B). No Demosponge is known, on
the other hand, which remains in the simple Rhagon condition ;
growth and folding of the wall lead in all cases to a series of pro-
gressive complications.

The simplest adult type of canal system in Demospongiae is
represented by such a form as Plakina monolopha (Fig. 61, f), in
which the upper wall or spongophare of the primitive Rhagon has
become folded to form a number of lobes or diverticula. The
flagellated chambers become restricted to the walls of the diverticula
in question, and open into their cavities, which, though in origin
simply portions of a continuous gastral cavity, may be distinguished
conveniently as excurrent canals from the gastral cavity proper, just
as the spaces enclosed between the folds of the spongophare may

Z

SPONGES 127

be termed incurrent canals, though in reality spaces external to the
sponge. A condition quite similar in the main to that seen in
Plakina monolopha, occurs also in Oscarella, which differs only in having
both apopyles and prosopyles drawn out into distinct aphodi and
prosodi, so that the very simple canal system in this form is of the
diplodal type (Schulze).

The further development of the canal system is brought about
by processes of growth perfectly similar to those already described
in the Calcarea Heterocoela; namely, on the one hand, by further
folding of the spongophare, leading to considerable branching and
complication of both the excurrent and incurrent canals ; and, on
the other hand, by thickenings of, and fusions between, the outer
ends of the diverticula of the spongophare, with the result, first,
that the incurrent spaces become more completely enclosed and

Fic. 85.

Diagram of a transverse section through the outer region of Tetilla pedifera. E, ectosome;
C, choanosome ; e, excurrent canal ; 7, incurrent canal; p, ostia. (After Sollas, ‘‘ Challenger”
Reports.)

narrowed to form definite canals; and secondly, that a cortical
layer is developed on the external surface of the sponge body.

An instructive stage in the evolution of the incurrent system
exhibiting but a slight advance on the state of things found in
Plakina monolopha, is seen in the Tetractinellid genus Tetilla (Fig. 85).
The dermal layer is greatly thickened at the distal extremity of
each diverticulum of the spongophare, and the outer free margin of
each such thickening is expanded into a rim or plate which unites
with the margins of other and similar thickenings to form a
continuous dermal membrane, perfectly comparable in its origin to
the pseudoderm often formed in an Ascon colony or the dermal
membrane of some Heterocoela. Over each incurrent canal the
dermal membrane is perforated by the dermal pores or ostia (stomions,
Topsent), while the true pores or prosopyles (chamber pores) are
now no longer visible on the surface. In consequence of these
advances in organisation, two regions of the sponge body can now

1 The presence of prosodi in Oscarella is disputed by some authors, and it is
possibly a variable character ; cf. p. 49, supra.

128 SPONGES

be distinguished : first, an external or enveloping portion, contain-
ing no chambers, termed the ecfosome ; and secondly, an internal
portion, containing the chambers, termed the choanosome. The —
former is a new acquisition; the latter constitutes the whole body
in such a form as Plakina monolopha or in the Rhagon. .

In correspondence with these changes the incurrent canal |
system can now be distinguished territorially, so to speak, into
two portions, the one lying in the ectosome, the other in the
choanosome. Each portion of the incurrent canal system may
exhibit very various modifications in different forms, as the result —__
of different modes of growth on the part of the ectosome. Simple

ee

Fic. 86.
Vertical section of Stelletta phrissens, Soll. Young specimen, showing the choanosome folded
within the cortex. 0, osculum. (After Sollas, ‘‘ Challenger” Report, x50.) . |

instances of the two extreme types of the incurrent system,
connected, nevertheless, by numerous transitions, are furnished by the
genus 7'etilla on the one hand, and by some species of the genus Plakina
on the other. In Zefilla (Fig. 85) the water on passing through the
dermal pores enters wide sinuses lying in the ectosome immediately ; |
beneath the dermal membrane, and these spaces can be distinguished
as subdermal cavities from the narrower portions of the incurrent
canals which traverse the choanosome. The distinction between the
ectosomal and choanosomal portions of the incurrent system is still
better seen in such a form as Sfelletta phrissens (Fig. 86), where the
incurrent canals proper are more narrowed, and contrast with the
wider subdermal cavities of the ectosome.

SPONGES 129

The species of Plakina, on the other hand, furnish an interesting
series of modifications of another type. In Plakina monolopha, as
_ we have seen, there is no ectosome (Fig. 61,/). In Plakina dilopha,
however, the distal extremities of the lobes of the choanosome are
greatly thickened over their whole outer surface, and coalesce
with one another to form a thick cortex, traversed by the much
narrowed incurrent canals. There are in this case neither
dermal membrane nor subdermal cavities, and the ectosomal
portions of the incurrent system are no wider, and may even be
narrower, than the choanosomal portions. Plakina trilopha carries
this state of things even further, the cortical layer being of greater
thickness, and the incurrent canals further complicated by secondary
folding of the choanosome. The incurrent canals may widen consider-
ably after traversing the ectosome, to form wide subcortical crypts,
lying in the choanosome, and therefore not homologous with the
subdermal cavities which, as we
have seen, belong to the ectosome.

The growth of a cortex, so well
seen in a simple condition in
Plakina, is carried to a high pitch
of development in many other
sponges, especially in the Tetracti-
nellids and their allies’ In a
typical corticate sponge the body is
enclosed in a tough fibrous rind,
often fortified by special differentia-
tions of the skeleton (Fig. 30, JS).
In such forms the incurrent canal
system may commence with an
arrangement known as a chone (Fig.
87), which may be taken as typifying
the extreme of differentiation under-
gone by the incurrent system. The
dermal pores (ostia) are grouped
to form pore sieves, and perforate

a thin membrane which roofs over
a funnel-shaped cavity, termed the
ectochone, situated in the cortex,
and therefore comparable to a sub-
dermal cavity. The ectochone
leads through a narrow aperture,
surrounded by a_ contractile
sphincter, into a spacious sub-

cortical crypt, termed the endochone.

the incurrent canals (sensu strictior?).

Fic. 87.

Section through the cortex of Cydoniwm
eosaster, Soll., showing the pore sieve over-
lying the chone, which communicates
through a sphinctrate aperture with the
subcortical crypt, lying in the choanosome
with its flagellated chambers. The dotted
circles in the cortex are sterrasters con-
nected by fibrous strands. (After Sollas,
“Challenger” Report, x73.)

From the latter come off

Although, in the instances described, the subcortical crypt

.

130 SPONGES

belongs to the choanosome and cannot therefore be compared with
a subdermal cavity, it would appear that in other cases a cortex
may be developed simply as a great thickening of the dermal mem-
brane, in which case the subcortical crypts may belong to the
ectosome and represent subdermal cavities. A cortex is, in fact,
a structure which can develop in different ways and may not be
homologous in different sponges. The term “subcortical crypt” is
to be understood therefore in a descriptive rather than in a
morphological sense.

The following table may serve to indicate the homologies of the
incurrent system in three typical cases :—

il 2 3
3 Dermal Cortex
= Membrane f
z 4 Cortex
= Subdermal | f Subcortical |
oa | Cavity Jf | \ Crypt f
L
wf :
2 f Subcortical |
S | Crypt f
ou f Incurrent ) f Incurrent |
= | \ Canals f \ Canals f
a f Incurrent |
= oh. \ Canals f

Each of the above types of the incurrent system may be combined
with different forms of the canal system considered as a whole,
especially as regards the relations of the chambers to the excurrent
and incurrent canals. As is plain from what has already been stated
with regard to the development from a Rhagon, the canal system
of Demospongiae always conforms to what has been termed above
the third type; but within the limits of this type of structure, it
may be either eurypylous, aphodal (Fig. 88), or diplodal (Fig. 89).
Hence the canal system as a whole is liable to very great structural
variations in the Demospongiae.

Skeleton.—The skeleton of the Demospongiae exhibits variations of
so divergent a character that it is not possible to discuss it in general
terms. We have to consider first those forms in which the skeleton
is composed of siliceous spicules, some or all of which are of tetraxon
type (Tetraxonida) ; secondly, those which always possess siliceous
spicules of monaxon form and never tetraxon (Monavonida) ; and
thirdly, those in which proper spicules—i.e. spicules secreted by
the sponge—are absent and the supporting framework is made up
of spongin fibres alone (Keratosa).

(a) Tetraxonida.—The siliceous spicules which compose the
skeleton of the Tetraxonida are divisible into megascleres and
microscleres—two categories which in the order Tetractinellida are
sharply distinct from one another, differing not only in size and

SPONGES 131

FI

3 88.

Transverse section across an excurrent canal and surrounding choanosome of Cydoniwm
eosaster, Soll. e, excurrent canal; s, flagellated chambers communicating with it by aphodal
canals ; i, an incurrent canal cut across ; s, a sterraster; 0, an oxea cut across. (After Sollas,

“Challenger” Report, X125.)

function, but also very frequently in morphological characters. Thus

certain forms of microsclere, such
as the commonly occurring asters,
conform to types of structure not
represented among the megas-
cleres. In this respect we find a
marked contrast with the Hexac-
tinellida, where all the spicules,
even the asters, are variations of
the one fundamental triaxon type.

Forms of the Spicules.—In the
first place, a distinction must be
drawn between the simple (prim-
ary) spicules, on the one hand,
and the compound (secondary)
spicules or desmas, characteristic of
the sub-order Lithistida, on the
other hand. Since the desma is
itself founded, in most instances,
upon a primary spicule, we may
commence with the discussion of
the latter.

All primary spicules in the

Fig. 89.

Diplodal canal system in Corticiwm cande-
labrum, O.S. e, excurrent canal ; the incur-
rent canal is shown on the left-hand side,
near its commencement in the cortex. (After
F. E. Schulze, x 200.)

132 SPONGES
ee 8 See
Tetraxonida may be considered ideally —that is to say, from a
purely architectural or geometrical point of view, and without
prejudice to the question of their actual phylogeny and evolution
—as modifications of one of two types: (a) the tetrazon type,
characteristic of the megascleres, though not confined to them ;
and ()) the polyaxon type, only found among the microscleres.
Strictly speaking, the tetraxon type itself could be considered as
a modification of the polyaxon, and has probably been derived
from it, but for practical purposes it is best to consider the two
types separately.

(a) Letraxon Type.—The simplest form of tetraxon spicule has four
equal and similar rays meeting at equal angles (Fig. 47, d and p)-
Such a spicule is known as a calthrops, and though of common
occurrence, both among megascleres and microscleres, it is far less
abundant than some of the numerous variations of the regular
tetraxon form. Departures from the fundamental type are brought
about, not only as in the Hexactinellida, by unequal growth or
curvature of the rays, or by the acquisition of secondary spines and
branches, but also, in contrast to the modifications of the triaxon
type, by variations in the angles at which the rays meet.

The simplest modification of the regular tetractine is one
correlated in the first instance with the acquisition by .it of a
definite orientation in the sponge body. One ray, which is directed
radially and points towards the interior of the sponge, becomes
differentiated from the three remaining rays, which in their
turn radiate more or less tangentially from a centre situated
close to the outer surface of the sponge. In this way arises the
form of spicule known as the triaene (Fig. 90, k, 1, m, n), which is
perhaps more than any other characteristic of the order Tetractinel-
lida. The radially directed ray of the triaene, which is usually
longer, but sometimes shorter, than the other three, is termed
the shaft or rhabdome, and the superficially situated rays are known
individually as the cladi or prongs, collectively as the cladome.

The triaene undergoes in its turn numerous modifications, affecting
every part of it, and giving rise to a series of forms, each denoted by a
special term. Without attempting to enumerate the many varieties of
the triaene, it is of interest to consider the variations of the cladi in their
relations to the rhabdome, both as regards orientation and size.

In the first place, the three cladi or their axes always meet one another
at equal angles, but the angles at which they meet the rhabdome may
vary considerably in different instances, though always the same for each
cladus in a given spicule. Hence, if a projection be made of the triaene
in such a way that the+shaft is completely foreshortened and seen
as a dot, then the axes of the three cladi, or of their main stems, if they
be branched, will appear to meet one another at equal angles of 120°.
If the triaene be viewed in profile, on the other hand, so that the shaft

|

SPONGES 133

and one of the prongs lie in the plane of the field of vision, then the
angle between shaft and prong may vary greatly. The cladi may be
directed forwards, 7.¢. so as to point the opposite way to the shaft (protriaene,
Fig. 90, 1); or outwards, at right angles to the shaft (orthotriaene, Fig.
90, x); or even backwards (anatriaene, Fig. 90,%). In other words, each
cladus may rotate in the plane of the rhabdome, the amount of rotation
being always the same for each prong of a given triaene.

In the second place, both the rays of the cladome and the rhabdome
may vary greatly in size relatively to one another, and any given ray may
become reduced until it finally disappears altogether. In the cladome the
process of atrophy, or rather arrest of development, may affect one ray
(diaene) or two of the rays (monaene), or finally, all three, the result in
the latter case being a simple monaxon spicule (Fig. 90, j), a form of

Fic. 90.

Types of megascleres in Demospongiae. «a-d, rhabdi (a, strongyle, b, tylote, c, oxea, d,
tylotoxea); e-g, ‘styli (¢, tylostyle, f, style, 9, spined tylostyle); h, branched monaxon ; j-9;
modifications of the triaene (j, cladi reduced, k, anatriaene, J, protriaene, m, orthotriaene, 7,
dichotriaene, 0, centrotriaene, p, amphitriaene, q, crepis of 7 ; rhabdocrepid, desma, s, older and
fully formed desma.

common occurrence in the Tetraxonida and known as a rhabdus (diactinal)
or style (monactinal). In cases where all the triaenes are reduced in this
way, the sponge may be entirely without tetraxon spicules, its Tetractinellid
affinities being shown only in secondary characters, such as the possession
of polyaxon microscleres or a cortex, and especially in the radiating arrange-
ment of the- large monaxon spicules themselves, an orientation easily
intelligible on the assumption of their derivation from the rhabdome of a
triaene. Instances of such forms are well seen in the Placospongidae and
Tethyidae. On the other hand, the modification of the triaene may pro-
ceed along a course exactly opposite to that which produces a monaxon,
the rhabdome becoming atrophied and leaving the three rays of the
cladome as a triactinal spicule usually situated close to the outer surface
of the sponge. .

As aberrant forms: of. the triaene may be mentioned finally the cases

/

134 SPONGES

in which the rhabdome is prolonged beyond the cladome (centrotriaene,
Fig. 90, 0), or bears a cladome at each extremity (amphitriaene, Fig 90, p),
and any of the varieties above mentioned of the tetractinal spicule, triaene,
or calthrops, may have one or more of its rays forked or branched like a
crest. The spicule is then said to be monolophous, dilophous, trilophous,
or tetralophous according to the number of rays so affected. When all
the rays are branched, the spicule may be termed simply a lophocalthrops
or lophotriaene. A special case of the latter is the candelabrum char-
acteristic of the Corticidae. Another common spicule, the dichotriaene
(Fig. 90, 2), has each cladus forked.

()) Polyaxon Type.—The most primitive form of polyaxon spicule
is a simple globule or siliceous concretion which, by the acquisition
of numerous spines or rays, becomes an aster. The latter in its
turn undergoes numerous modifications, of which we may note in
the first place two series, in one of which the rays meet at a
common centre (euaster, Fig. 48, m, n), while in the other the rays
are not centred, but radiate from a longer or shorter axis, usually
spiral (streptaster, Fig. 48, d, e).

Further variation of each of these two sub-types gives rise to a great
number of forms. We may notice specially certain forms of systematic
importance, as, for example, the sterraster (Fig. 47, g), in which an aster
with numerous rays (in some cases apparently a euaster, in others a
streptaster) becomes converted secondarily into a solid spherule by deposits
of silica between the rays; the spiraster, a streptaster with a spiral axis
(Fig. 48, d); the amplhiaster, a streptaster with the rays confined to two
whorls at each end of the axis (Fig. 48, f); the sanidaster (Fig. 48, e);
and the two modifications of the euaster, termed respectively oxyaster
and sphaeraster (Fig. 48, m, »). Of great morphological importance, on
the other hand, are the variations of the aster produced by reduction of
the rays (Fig. 48, 0, p). Thus a euaster with only four persistent rays
becomes a microcalthrops (Fig. 48, p) or primitive tetraxon, which, by
curvature, branching, or ornamentation of the rays, gives rise to a large
series of microscleres, while increase of size makes it the starting-point
of the evolution, wholly or in part, of the megascleres. By a further
reduction of the rays of the euaster to two placed in the same straight
line, or, it may be, by suppression of the spines and elongation of the
axis, in a streptaster, we obtain a minute monaxon or microrhabdus, itself
the ancestor, so to speak, of many forms of microscleres, and perhaps of
megascleres; of the former, the sigmaspire (Fig. 48, a, b), perhaps
derived immediately from a spiraster by suppression of the rays, deserves
special mention.

Secondary Spicules or Desmas.—There remain for consideration
the remarkable megascleres known as desmas (‘“ clones,” Rauff),
characteristic of the sub-order Lithistida. Each desma is formed
typically by secondary deposits of silica upon a true spicule termed
the crepis or foundation, which undergoes an arrest of development.

SPONGES 13

wt

The crepis may be a minute calthrops, or a rhabdus, or, finally, may
be atrophied completely ; thus fetracrepid, monocrepid, and acrepid
desmas may be distinguished. The layers of silica deposited are at
first concentric with the crepis, but subsequently grow out into
irregular branches and tubercles, which are quite independent of it.
In this way a secondary skeletal element of complicated and often
quite irregular form is produced (Fig. 47, f ; Fig. 90, q, 7, s).

Phylogeny of the Spicules—Enough has been said to indicate the
probable origin of the primitive tetraxon from the polyaxon aster or
globule, and hence the origin of all megascleres from the microscleres.
The regular tetraxon type of spicule represents an adaptation to the
structure of a primitive Rhagon-like ancestor, in which, by folding of the
walls, numerous spherical ciliated chambers lie embedded in a parenchyma-
tous tissue (Schulze). When in such a form, the chambers are as closely
packed as possible ; each chamber is in contact with three others, and
the tetraxon spicule fits exactly into the interspaces between four con-
tiguous chambers.

The evolution of many of the forms of spicules is difficult to follow
in detail, since in many cases more than one origin is possible for them,
and not enough is known to determine with certainty which was the
actual course of the phylogeny, which may indeed have proceeded along
more than one direction. Thus in the case of the characteristic triaenes :
while, on the one hand, a general comparative survey of their morphology
and systematic relations rather indicates an origin for them from the
primitive tetraxon calthrops, correlated with the acquisition by the sponge
of a distinct cortex ; on the other hand, their ontogeny, so far as it is
known, and also the existence of certain forms such as the mesotriaene
and amphitriaene, favours the view that they have originated by branch-
ing of a large monaxon rhabdus (Sollas). Conversely, a double origin is
possible for the monaxon megascleres, either by reduction from a triaene,
or, by increase of size, from a microrhabdus, derived in its turn from
reduction of an aster or a calthrops.

The following scheme may serve to indicate the different courses of
phylogeny which are possible :—

Globule

Primitive =. euaster > calthrops > triaene
or Coneretion }

> streptaster -—> microrhabd. -—> macrorhabd.

Arrangement of the Spicules in the Skeleton.—By the arrangement
of the megascleres two types of skeleton can be distinguished in the
order Tetractinellida: the crregular, seen in the Lithistida, and a few
Choristida ; and the radiate type (Fig. 91), characteristic of the vast
majority of Choristida. Even in the former type, however, all
triaenes when present near the surface have the rhabdome directed
towards the centre, and to this extent exhibit a radiate structure.

In most, if not all, Choristida the young sponge has a radiate structure
when still quite small, the spicules being arranged in sheaves between

136 SPONGES

the incurrent folds of the canal system, with their main shafts reaching
from the centre to the periphery (Fig. 91). During subsequent growth
the new spicules, which are
formed after the sponge has ex-
ceeded a certain size, may in a

larly, so that the full-grown
sponge exhibits no trace of the
radiating arrangement, except
perhaps close to the outer sur-
face ; most usually, however, the
spicules formed later retain the
radial arrangement, so that the
spicule sheaves of the earlier
stage are converted into fibres
radiating from the centre to the
periphery, often with a pro-
nounced spiral twist.

10. Al. The surface of the sponge
Mode of arrangement of spicules in a young May become “hispid ; by the
Souaa) sponge, Dragmastra normant, Soll. (After projection of radially arranged
spicules beyond the limiting
epithelium of the body wall, and the “hispidating ” spicules may be
specially differentiated to form protecting fringes round the openings
of the oscula and incurrent canals, or to furnish a root tuft similar
to that of some Hexactinellida. A characteristic feature of Tetracti-
nellids is the differentiation of a special cortex, which may have
a skeleton distinct from that of the pulp, both as regards arrange-
ment and’ composition (cf. Fig. 87). Finally, in those forms in
which there is an elongated oscular tube, it is supported by a
palisade of special spicules forming a cloacal skeleton.

The microscleres are found scattered in the parenchyma, and
may be sharply differentiated in the two regions of the body, cortex,
and pulp.

Union of the Spicules—Spongin is said to be present in
minute quantities in some forms, but it never has any appreciable
importance,' and is practically absent, as also any other form of
special cementing substance. The spicules are held together by
interlocking and by the fibrous cortex. In Choristida they fall
apart when macerated. In the Lithistida, however, the complicated
desmas interlock by means of the tubercles or their branches to
form a compact skeletal framework which imparts to the sponge a

1 With the exception of Zhymosia, which is described as having a skeleton of
spongin fibres radiating upwards from the base. Each fibre is “ verrucose,” being
composed of nodules of spongin agglomerated together, and contains no foreign bodies
(Topsent). More evidence seems to be needed as to the true nature of the fibres in
question.

few instances be disposed irregu-_

tome

_—

SPONGES 137

J

stony hardness. This mode of union of the spicules is termed
“ zygosis.”

(8) Monaxonida.—The skeleton of the Monaxonida is composed
of siliceous spicules, to which may be added a greater or less
amount of spongin. The function of the latter is, in the first in-
stance, that of a special cement, which glues the spicules together,
but it may be present in such quantities that it forms the greater
part of the skeleton, especially in forms whose habitat exposes them
to severe stresses and strains from waves and currents (Keller).
Hence the spicules are thrown more and more into the background,
and tend to become reduced and rudimentary. In any case, the
spicules of Monaxonida are, as a general rule, smaller relatively to
the size of the sponge than is the case in Hexactinellids and
Tetractinellids, and in order to support the sponge adequately,
they tend to become united to form more or less definite tracts of
fibres, a type of skeleton which has the further advantage of pos-
sessing the flexibility and elasticity essential to a shore life.

The formation of a skeletal framework by union of spicules,
permits of a sharp distinction being drawn, as a rule, between
megascleres and microscleres, since the former enter into the com-
position of the body skeleton (skeletal spicules), while the latter
are scattered in the tissues (flesh spicules). In some cases, how-
ever, the distinction is one of degree and scarcely tenable, as in the
Spongillinae. In many cases microscleres may be wanting entirely.

Forms of Spicules—All spicules in this group are either of the
monaxon type, or in a few cases among the microscleres, polyaxon.
Since, however, monaxon spicules are of frequent occurrence in
other groups as reductions of triaxon and tetraxon types, it is not
so much the presence of monaxons, as the absence of other types,
which specially characterise the Monaxonida.

(a) The megascleres are always monaxon, and their variations,
though numerous, are within a small compass. The most import-
ant distinction that can be drawn depends upon the spicule being
monactinal (styli, Fig. 90, ¢, f, g), or diactinal (rhabdi, Fig. 90, a-d).
In the former case, the slight swelling in the axial thread that
marks the starting-point of the growth is near one extremity,
which may be termed the proximal end of the spicule; in the
latter case, it is near the middle of the shaft. Monactinal spicules
always have the two ends unlike, the proximal end being rounded
off abruptly, and often knobbed (“tylostyle”). Diactinal spicules,
on the other hand, usually have the two extremities similar.

Other variations in the monaxon spicule, apart from fluctuations of
size, depend on whether the shaft is smooth or spined, straight or curved,
or whether the extremities are sharp (“oxeote”), blunt (“tornote ”),
rounded (“strongylote”), knobbed (“tylote ”), or, in rare cases, branched.
The branching is probably due, in most cases, to the development of

138 SPONGES

spines, which are restricted to the termination of the shaft, and in some
cases assume the character of a grapnel (Proteleia, Acarnus). In the
interesting genus Trikentrion, however, the spicules which echinate the
skeletal fibres (see below) are branched at their inner end so as to have
two, three, or even four roots by which they are attached to the skeletal
fibre, and the branching here affects the axial thread, producing some-
times an imitation, as it were, of a tetraxon spicule (Fig. 90, h).

(b) The microscleres, though usually monaxon, exhibit a wider range of
variation than is to be found amongst the megascleres, owing to their
being usually strongly curved or provided with prominent hooks or
spines. In this way arise certain constant forms, often of great system-
atic importance, such as the sigma (Fig. 48, a, b, g), the toxa, the chela
(Fig. 48, h), specially characteristic of the family Poeciloscleridae, and the
peculiar amphidiscs, developed in connection with the gemmules of some
Spongillinae (Fig. 56, amph).

Of the polyaxon type, both streptasters and euasters are met with,
the latter form being, however, of rather exceptional occurrence. It is
extremely probable, moreover, that, with few exceptions, the streptaster,
when found in this group, represents a minute spined rhabdus, in which
the shaft has become shortened and the spines lengthened, and should
therefore be regarded as of the monaxon, rather than of the polyaxon
type. Spined rhabdi are of common occurrence as microscleres, and in
the Spongillinae they seem to be of caenogenetic origin and derived from
megascleres. The euaster would appear, in at least one family (Axinel-
lidae, to represent a further step in the reduction of a monaxon strept-
aster. In the other cases, where euasters occur (e.g. Tethyidae), the true
affinities of the sponges that possess them are shown by various secondary
characters to be with the Tetractinellida rather than with the typical
Monaxonida, and the spicules in ‘question may in such forms be regarded
as primary euasters of the true polyaxon type, derived from a Tetraxonid
ancestor which has recently lost its tetraxon spicules.

Union of the Spicules and their Arrangement in the Fibres.—
Secondary siliceous deposits, for the purpose of uniting the spicules
into a framework, are unknown in this group, though in the
Spongillinae peculiar spicular systems of branching form, due to the
fusion of several independent monaxons, are of common occurrence
as an abnormality or variation which may become so frequent that
in some cases it must be considered as a normal feature of certain
species (Evans, 1899).

Union between the spicules is effected either by means of
fibrous tissue or by spongin. A well-marked series of gradations can
be made out in this respect. In the most primitive types the
spicules are held together, if at all, by fibre cells. In the next
stage there are to be found amongst the fibre cells a certain number
of glandular cells (“spongoblasts”), derived from the external
epithelium (see above, p. 46), which become included in the
growing fibres and secrete spongin. Next the number of spongo-

g . . : bad

SPONGES 139

blasts, and consequently the amount of spongin, increases pari
passu with a decrease in the number of fibre cells, which tend to be
placed externally to the spongoblasts (cf. Fig. 92, A, B). Finally,

the spicules become wholly enveloped in spongin, the result being
a fibre of spongin containing a core of spicules, the whole enveloped
in a fibrous sheath (Fig. 92 °C). A still further stage, in which the

ee Ih AOS
! rae
Wo Le

Fic. 92.

The evolution of a spongin skeleton as seen in types of Renierinae and Chalininae and in
Euspongia. A, skeletal framework of Reniera; B, of Pachychalina; C, of Chalina; D, of
Euspongia. sp, spicules; spg, spongin; m.f, main fibres ; c.f, connecting fibres ; spat, spongin
fibres ; con, conulus.

spicules in the interior of the fibres atrophy and disappear (Fig. 92,
D), produces a type of sponge skeleton which can only be dis-
tinguished froin that of the Keratosa by arbitrary definitions
(presence or absence of spicules outside the fibres). The place of
the spicules is taken in many cases by sand grains or foreign
particles of various kinds.
There can, in fact, be found in the Monaxonida every possible
stage required for the phylogeny of the true horny sponges
12

7

(Dictyoceratina)—an evolution which has probably taken place in
more than one family of Halichondrina.

140 SPONGES

When distinct skeletal fibres are present, they are built up of spicules
according to one of three distinct patterns or types, which have been
named from the families or sub-families which they characterise.

(1) In the Renierine or Chalinine type the fibre is made up of
spicules, all of which lie parallel to the direction of the fibre. The
spicules may be arranged in a single series, end to end, or in more than
one such series (Fig. 92, A-C, and Fig. 93, A).

(2) In the Axinellid type each component spicule is inclined at a
variable, but usually acute, angle to the axis of the fibre, giving it a
feathery or ‘ plumose” appear-
ance. The spicules so placed
are said to “echinate” the fibre
(Fig. 93, B).-

(3) The Ectyonine type of
fibre combines the peculiarities
of the other two types, since it
is made up of a core of parallel
spicules covered by a superficial
layer of echinating spicules,
which are very rarely sitnilar
to those occupying the axis
(Fig. 93, C).

Arrangement of the Skeleton
alynes, of tkcltal thre in the Moneronida. 4 at Large.—In the more typical
Ectyonine type. Halichondrina the © skeletal

fibres have a reticulate arrange-
ment, in which primary fibres, runfiing vertically towards the sur-
face of the sponge, can often be distinguished from secondary fibres
crossing them at right angles (Fig. 93, A, B, and C). In the Suberitidae
and many Clavulina, and to some extent in the Avinellidae, the fibres
have a more radiate arrangement, running from a centre or axis to the
surface without any crossing fibres.

In most Monaxonida,’ whatever the general arrangement of the
skeleton may be, a dermal skeleton can usually be distinguished from a
main skeleton. In other respects, however, the skeleton shows very little
specialisation in different regions. A root tuft is never present.

SSS

WS

Fig. 93.

(y) Keratosa.—In the horny sponges the skeleton consists of
fibres of spongin, which in one instance, DVarwinella, are found
combined with isolated spicules of the same substance. * |

The spongin fibres of Keratosa consist typically of two portions,
a softer and more granular medullary substance, occupying the axis,
surrounded by concentric coats or lamellae of true spongin, forming
the cortical substance. According to the proportions of these two
constituents, two types of fibres are conveniently distinguished.
In the solid or homogeneous fibres, the axial substance is very small

SPONGES 14!

in amount, and possibly absent altogether in some cases. In the
hollow or heterogeneous fibres, on the other hand, the medullary
substance is largely developed, making up often the bulk of the
fibril, but relatively less abundant in the older fibres than in the
younger.

In form the spongin fibres are usually cylindrical, but may be
slightly compressed and even flattened or leaf-like in places
(Dendrilla). The growing portions of the spongin fibre are
enveloped in a sheath or “mantle” of spongoblast cells, of columnar
epithelial form, which appear to deposit concentric layers of spongin,
as a cuticular secretion, upon the surface of the fibre. Many
details of the growth remain, however, obscure and in need of
further investigation, especially as regards the origin of the
medullary substance.'

When the fibres have attained their definitive growth, the
spongoblasts seem to disappear, perhaps becoming converted into
connective tissue cells. :

As regards the arrangement of spongin fibres to form the
skeleton as a whole, two types can be distinguished, the reticulate
and the dendritic. In the reticulate type the skeleton is made up
of a continuous network of anastomosing fibres, in which principal
and connecting fibres can be distinguished. The former (Fig. 92, D,
mj) run vertically upwards to the surface and raise it up into
little tent-like projections or conuli. The connecting fibres take
amore horizontal course. In the dendritic type, characteristic of the
family Aplysillidae, the skeleton consists of heterogeneous fibres which
grow upwards like a tree from a basal plate of spongin, branching
freely, but remaining distinct from one another. The terminal
branches raise the skin into conulii In the genus Darwinella a
skeleton of this kind is found combined with separate spicules of
spongin having the same structure as the fibres of the skeleton.
The spicules in question are of variable form, but in many cases
distinctly of a six-rayed or triaxon type; the rays vary, however,
from two or three to as many as eight, and the angles at which
they meet are irregular and inconstant. Nothing is known
regarding their origin and formation.

The property possessed by many sponges of taking up foreign
bodies into their fibres has already been noticed (p. 42). In the

1 According to Lendenfeld, whose results require confirmation, the medullary
substance in Dendrilla owes its origin to cells derived from the spongoblast layer,
which become included in the fibre at its growing point. The function of these cells
is supposed to be the production of medullary substance by destruction and modi-
fication of the layers of cortical spongin secreted by the enveloping spongoblasts, and
they are hence termed by Lendenfeld ‘‘ spongoclasts,” on the analogy of the marrow
cells or osteoclasts of Vertebrata. Cells are also stated to occur in the horny fibres
of the genus Janthella, but in this case they are found between the spongin lamellae

of the cortical layer, and not at all in the medullary substance. In no other cases
have cells been observed in the interior of the fibres,

a

142 SPONGES

Keratosa, included foreign bodies are always absent in the fibres
of the dendritic type of skeleton; on the other hand, they are
commonly present in the fibres of the reticulate type, a difference
perhaps due, as already suggested above (p. 43), to the fact that
the former grow originally from the base of the sponge, while the
latter, on the contrary, have, from the first, their growing points at,
or near, the upper surface of the sponge body. As regards the
amount of foreign bodies taken up by different sponges, a complete
series of gradations can be traced. Starting from forms which, like
the common bath sponge, have no foreign bodies at all, or only a
few, in their principal fibres, we find others in which the amount
contained in the principal fibres is greatly increased, the connecting
fibres, however, still being free from them; in others again, both
principal and connecting fibres are loaded with foreign bodies
(Fig. 94). Finally, the whole skeleton appears to be made up of
sand grains and similar particles, between which the spongin can
scarcely be made out. In fact, in many of these so-called arenaceous
sponges the presence of any spongin at all in the skeleton is
disputed.

Thus in Psammopemma, an extreme type, the skeleton is made up of
isolated sand grains, which are stated to be coated each by a thin cuticle
(Marshall) composed of spongin (Poléjaeff), and to be united one to another
by thin strands of the same substance (Lendenfeld). Haeckel, however,
denies the existence of any spongin connecting the sand grains, and has
founded a new family, Psamminidae, characterised by a skeleton of
foreign bodies without any spongin, for the genus Psammopemma and its
allies.

Two aberrant types of spongin skeleton have been described by
Haeckel (1889). In his genus Cerelasma, placed by him amongst the
Spongelitdae, the skeleton is described as consisting of thin spongin
lamellae, which branch and anastomose to form a reticular framework.
In the meshes of the skeleton are lodged numerous foreign bodies, each
as a rule enveloped in a thin coating of spongin. In Haeckel’s family
Stannomidae the skeleton is said to be composed of thin fibrillae of
spongin, which may branch but do not anastomose, and between which
numerous foreign bodies lie in the gelatinous ground substance. Grave
doubts attach, however, to the nature both of Cerelasma and the
Stannomidae, and it is very probable that they are not sponges at all
(see p. 154).

There remain for mention, finally, the peculiar filaments found in
certain genera (Hircinia, Stelospongus, ete.), combined with a spongin
skeleton of the ordinary type. Each filament is a long slender twisted
thread, slightly thicker in the middle than towards the extremities, and
terminating at each end in a knob. The form has been aptly com-
pared to that of an ordinary skipping-rope, with pear-shaped handles.
Each filament has a thin sheath enclosing a softer medulla, traversed
from end to end by an axial thread. The greatest uncertainty prevails

a

SPONGES 143

as to the true nature of these structures. Their chemical nature has
been shown to be different from that of spongin (Schulze) ; but while
some authors are inclined to regard them as foreign to the sponge, and
probably organisms of a symbiotic or parasitic nature, others consider
them as true products of the sponge tissues. Haeckel, amongst the latter,

Fic. 94.

Spongin fibres of Spongelia avara, loaded with foreign particles. pr. f, principal fibre ;
conn. f, connecting fibre. (After F. E. Schulze.)

compares them with the fibrillae of Stannomidae, while Fol professes to
trace their origin to fusiform cells of the connective tissue layer, and
» considers that the family Filiferae (O. Schmidt) should be reinstated for
the horny sponges characterised by the possession of filaments. Loisel
suggests that they are intracellular spongin filaments of the same nature

144 SPONGES

_—_———q—_m -

as the elastic fibrillae described by him in Reniera. The question cannot
at present be decided.

Phylogeny of Keratose Skeletons—In dealing with the Monaxonida, the
evolution of the pure spongin fibre, by gradual increase of the spongin and
atrophy of the spicules in the skeletal fibres of that group, has already
been traced (see above, p. 139). It is highly probable not only that most
Keratose skeletons have so originated, but that the evolution of spongin
tibres has taken place in this way more than once in different families of
Monaxonida independently. On the other hand, it is not improbable that
the dendritic fibres of the Aplysillidae may have originated in a different
way, which, however, it is not possible to indicate satisfactorily at present.

After loss of the spicules, many sponges have acquired the habit of
iaking up foreign bodies into their fibres, a habit which reaches its
extreme in the arenaceous Spongeliidae. Should some of these forms
prove to be really devoid of spongin, an interesting speculation is opened
up as to how far such a condition is the culminating point in an evolution
which proceeds by diminution and ultimate loss of spongin ; or whether
it is a more primitive state of things, spongin never having been present.

Histology—As has been already remarked, the Demospongiae attain
to a higher degree of histological differentiation than either the Calcarea
or the Hexactinellida ; while in the two latter classes we can scarcely
recognise more than the six categories of cells indicated by Roman numerals
in the table given above (p. 62), in the Demospongiae each of these cell-
species may be further differentiated into the several cell-varieties indicated
in our table by Arabic numerals. Since these many forms of cells have
already been fully described above, we need not further discuss them
here. It should, however, be pointed out that our knowledge of the
histology of Demospongiae is still in a very backward condition, and that
it is extremely difficult to refer with certainty the numerous forms of cells
to their proper position in a phylogenetic classification of the histological
elements. Amongst the authors who have especially contributed to our
knowledge of these questions in recent years, Topsent deserves especial
mention as having been the first to show the connection of the myocytes
and the epithelium, and also as having demonstrated the existence in all
Demospongiae of cellules sphéruleuses. The latter are almost certainly
homologous, as pointed out above, with the porocytes of Calcarea, although
their connection with pores has not yet been demonstrated and may not
exist. In support of this conclusion, reference may be made to the recent
investigations of Loisel, above described.

Embryology.—The structure and metamorphosis of the larvae of
Demospongiae has been dealt with above at sufficient length. We may
refer, however, to two points of interest. The first is the striking fact
that in the whole group of Tetractinellida, comprising as it does many
abundant shore forms, no larvae are as yet known, The second is the
occurrence, in the larvae of Monaxonida, of diagnostic characters corre-
sponding to the systematic position of the adult sponges (Maas), Thus
in Haploscleridae the larva has a pigmented ring at the posterior pole, the
pigment being chiefly lodged in a circle of larger flagellated cells, which
bear flagella of a special type, and mark the posterior limit of the

:

SPONGES 145

flagellated layer. In the families Poeciloscleridae and Awinellidae there is
no such ring of special flagellated cells, and the whole flagellated layer
is pigmented, while the exposed portion of the inner mass is unpigmented.
This may be compared to the way in which the families Clathrinidae and
Leucosolenvidae, amongst Ascons, are characterised by the possession of
parenchymula and amphiblastula larvae respectively.

Classification.—The subdivision of the class Demospongiae is a
matter of great difficulty, and one upon which little agreement is
to be found amongst the authorities ; not because the mutual affini-
ties of the various forms comprised in this group are not clear, but
on account of the very frequent occurrence of convergent evolution
and parallel adaptations. The characters which. can most con-
veniently be used for defining and delimiting systematic groups,
and above all, the characters of the skeleton, have not always a uni-
form origin, and therefore do not indicate natural relationships.
It may, indeed, be said that at present, at any rate, it is not
possible to construct a system which shall be at once strictly logical
and perfectly natural. The most obvious and simple classification
is into four grades, characterised respectively (1) by the possession
of tetraxon spicules, (2) by monaxon spicules, without tetraxons,
(3) by a horny skeleton, without siliceous spicules, and (4) by the
absence of a skeleton of any kind. If these four groups are to have
any pretence to being natural, however, it is absolutely necessary
to overstep in every case the limits imposed by rigidly logical
definitions. Thus in the first sub-class, Tetraxonida, it is necessary
to include such forms as Placospongidae and Chondrosidae which lack
tetraxon spicules and sometimes even spicules of any kind, but
whose affinities with the other families of the sub-class are indicated

_ by a number of secondary characters. In the Monaxonida we have
three sub-orders which are less closely allied to one another than to
forms outside the group, and the same must be said of the two
orders of Keratosa. The climax is reached, however, when we come
to the so-called Myxospongiae, forms devoid of a skeleton. In the
first place, we have to remove Chondrosia, which, as has been said,
is undoubtedly a degenerate Tetraxonid. Of those that remain,
Oscarella is certainly a very close ally of Plakina, among the Tetraz-
onida, while Hexadella, and probably also Halisarca, seem to have
close affinities with the Dendroceratina amongst the horny sponges.
So long, however, as it is by no means certain, in the case of these
forms, whether their lack of a skeleton is due to degeneration, or
represents, as seems more probable, a primitive feature, and until
there is more evidence bearing upon this point, the genera in ques-
tion, in spite of their divergent affinities, may well be left as a sub-

_ class together, as representing, perhaps, a more primitive grade
of organisation than any other Demospongiae. It is inevitable
that any system at present proposed should be more or less of a

146 SPONGES

compromise between logical necessities and natural affinities. It is
hoped that the classification here adopted represents such a com-
promise in which the disturbance of the true relationships is reduced
to the unavoidable minimum.

The following scheme represents the four main sub-classes and
their principal orders. By means of brackets placed on the right,
the(perhaps) more natural affinities of the sub-groups are indicated :—

CLASS DEMOSPONGITAE (SoLL.)

GRADE I. TETRAXONIDA (Ldf.) )

Order 1. Carnosa (Crtr.), Tops. ae
,, 2. Tetractinellida (Marshall). 2
GRADE II, Monaxonipa (R. and D.) 5 3
Order 3. Hadromerina (Tops.) a
Sub-Order 1. Aciculina (Tops.)
Sub-Order 2. Clavulina (Vosm.)
Order 4. Halichondrina (Vosm.) S 39
Grape III. Keratosa. E 8 B
Order 5. Dictyoceratina. BE e
,, 6. Dendroceratina. led =
Grape IV. Myxosponaipa (Soll.) = 3 H
— 5?

Family 1. Halisarcidae (O.S.)
2. Oscarellidae (Ldf).

”?

DETAILED CLASSIFICATION OF THE DEMOSPONGIAE.

GRADE I. TETRAXONIDA.
Demospongiae typically with tetraxon spicules.

ORDER 1. Carnosa (Crtr.), Tops. emend.
Tetraxonida with the spicules greatly reduced in size, and even want-
ing ; no diactinal megascleres or triaenes with long rhabdomes.

Sus-ORvDER 1. *MacrorriaENnosa, Tops.

The characteristic spicules are triaenes with short rhabdomes, not
specially differentiated in the ectosome or the choanosome, and often
variously ornamented or of aberrant types (amphitriaenes, mesotriaenes,
ete.); microscleres of various kinds. A heterogeneous collection of
sponges, of diverse affinities: “chainons de chaines brisées, dérivés sans
intermédiaires connus” (Topsent). Not divided into families, Genera—

+ Recent and fossil.

SPONGES 147
FDercitus, Gray [Cret.]; Corticella, Soll.; Rhachella, Soll.; Thrombus,
Soll. ; Samus, Gray ; *Ditriaenella, Hinde and Holmes [Eoc.].

Sup-OrRDER 2. MicROSCLEROPHORA, Soll.

With tetraxon spicules of small size, comparable to microscleres.

Famity 1. 7Corticrpar, Vosm. With dense sarcenchymatous choano-
some and tough chondrenchymatous ectosome; spicules microcalthrops
and candelabra, the latter localised at the surface of the body. Genus—
7 Corticium, O.S. [Eoc.]. Famity “2. Praxrnipas, F.E.S. Choanosome of
loose, lacunar structure, collenchymatous; the chondrenchymatous ectosome
searcely or not at all developed; spicules microcalthrops and their
deri¥atives, either by reduction (triactines, rhabdi) or by complication
(branching of the rays). Genera—tPlakina, F.E.S. [Eoc.]; Placortis, F.ES. ;
Plakinastrella, F.E.S.; Plakinolopha, Tops. (Here Oscarella finds its
nearest allies.)

Sus-ORDER 3. OLIGosILicina, Vosm.

Corticate sponges without tetraxon spicules ; siliceous skeleton reduced
to polyaxon microscleres (Chondrilla) or wanting entirely. Fammy—
CHoNDROSIDAE, F.E.S.; Genera—Chondrosia, Ndo.; Chondrilla, OS. ;
Thymosia, Tops.

ORDER 2. Tetractinellida (Marshall), Topsent, 1894.
Tetraxonida typically with triaene megascleres, or with desmas.

Sus-ORpDER 1. CHoristIpDA, Soll.
No desmas ; spicules never articulated to form a coherent skeleton.

TRIBE 1. SIGMATOPHORA, Sollas.

The microsclere when present wa sigmaspire.

Famity 1. TETILuIpAg, Soll. With protriaenes, always present, and
sigmaspires, often wanting. Genera— Tetilla, O.S.; Chrotella, Soll.
Cinachyra, Soll.; Craniella, O.S.; Tethyopsilla, Ldf.

TRIBE 2. ASTROPHORA, Soll.

One or more of the microscleres is an aster.

Demus a—Streptastrosa, Soll. One of the microscleres is a spiraster
or, when this is not the case, one of the megascleres is a calthrops. ;

Famity 2. THENEIDAE, Soll. Megascleres, triaenes; microscleres,
spirasters, and amphiasters ; the ectosome does not form a cortex ; ground
substance collenchymatous ; canal system eurypylous. Genus—j7Thenea,
Gray [Cret.], (Fig. 24). Famriy 3. TPACHASTRELLIDAE, Crtr. Megascleres,
calthrops, and rhabdi; microscleres, spirasters, and microrhabdi. Genera
—7Pachastrella, O.S. [Carb. Cret. Eoc.]; Calthropella, Soll. ; Characella,
Soll. ; Poecillastra, Soll. ; Sphinctrella, O.S.; + Triptolemus, Soll. [Eoc.]}.

Demus S—Evastrosa, Soll. Euasters always present, never spirasters
or sterrasters ; triaenes, but never calthrops amongst the megascleres.

* Fossil forms.

148 SPONGES

Famity 4, STELLETTIDAE, Soll. Megascleres, triaenes, and rhabdi ;
canal system aphodal; ground substance of choanosome sarcenchymatous.
Sus-F amity (a). Homasterta, Soll. Never more than one form of aster.
Genera—Myriastra, Soll.; Pilochrota, Soll. Sun-Famry (b). tEvaste-
RimnA, Soll. With two kinds of euasters. Genera—Anthastra, Soll. ;
* Geodites, Crtr.[Cret. Eoc.]; tStelletta, O.S, [Cret. Eoc.]; Dragmastra, Soll.
Sus-Famity (c). SANIDASTERINA, Soll. With euasters and sanidasters or
amphiasters. Genera— Ancorina, O.S.; Tribrachion, Welt. (Fig. 25) ;
7 Tethyopsis, Stew. [Cret.]; Disyringa, Soll. (Fig. 26); Stryphnus, Soll. ;
Seiriola, Han. ; Sanidastrella, Tops.) Sup-Famity (d). RHABDASTERINA,
Soll. With euasters and microrhabdi. Genera— Ecionema, Bwk. ;
Papyrula, O.S.; Psammastra, Soll. ; Penares, Gray ; Algol, Soll.

Demus y—Sterrastrosa, Soll. The characteristic microsclere a sterr-
aster.

Famity 5. tGeopmpar, Gray. With triaenes. Sus-Famity («).
yEryurma, Soll. Megascleres, orthotriaenes, and rhabdi, never ana-
triaenes or protriaenes; somal microsclere a microrhabdus or spherule.
Genera—t Erylus, Gray [Eoc.]; Caminus, O.S.; Pachymatisma, Bwk.
Sup-Famity (6). tGroprna, Soll. Megascleres rhabdi, orthotriaenes, or
dichotriaenes, frequently also protriaenes and anatriaenes. Somal micro-
sclere, an aster with numerous rays. Genera—Cydonium, Flem.; tGeodia,
Lam. [Cret.]; Synops, Vosm. ; Isops, Soll. Faminy 6. 7PLACOSPONGIDAE,
Gray. Megascleres pin-shaped monaxons (“tylostyles”), no triaenes.
Genera—Placospongia, Gray ; Antares, Soll. ; Physcaphora, Han. ; *Rhax-
ella, Hinde [Jur.].

Genus tincerti sedis—* Ophirhaphidites, Crtr. [Cret.].

Sup-OrperR 2. Liruistrpa, O.S.

Tetractinellida with a rigid skeleton, due to interlocking of special
(secondary) spicules, desmas.

The classification which follows is that of Sollas, founded upon a study
of the living forms. In addition there are numerous fossil forms, not
sufficiently well characterised to be assigned a definite place in this
system, such as the family Rhizomorina of Zittel, which should be divided
amongst the two families Corallistidae and Azoricidae ; these will be found
appended at the end of the system. The new groups and families created
by Rauff, whose studies are not yet completed, are indicated in square
brackets in their proper places.

Tree 1. Hopropsora, Soll.

With special ectosomal spicules and usually some form of microscleres.

Demus a—7Triaenosa, Soll. The ectosome contains megascleres,
typically triaenes, sometimes, however, monaxons (styles—Desmanthidae ;
rhabdi—Sulcastrella) ; canal system aphodal.

Famiry 1. 7Terractapmar, Z. With tetracrepid desmas and micro-
scleres. Genera—?Theonella, Gray [Eoc.]; tDiscodermia, Boe. [Eoe.];
Racodiscula, Z.; Kaliapsis, Bwk.; Neosiphonia, Soll.; Rimella, OS. ;

Collinella, O.S. (Fig. 28, B); Sulcastrella, O.S.; *Phymatella, Z. [Cret.];

* Aulaxinia, Z. [Cret.]; *Callopegma, Z. [Cret.]; *Trachysycon, Z. [Cret.] ;

q

:
.

SPONGES 149

*Siphonia, Park. [Cret.], (Fig. 27); *Jerea, Lamx. [Cret.]; *Polyjerea,
From. [Cret.]; *Bolospongia, Hinde [Cret.]; *Astrocladia, Z. [Cret.];
*Thecosiphonia, Z. [Cret.]; *Calymmatina, Z. [Cret.]; *Turonia, Mich.
[Cret.]; *Kalpinella, Hinde [Cret.]; *Thamnospongia, Hinde [Cret.] ;
* Pholidocladia, Hinde [Cret.]; *Ragadinia, Z. [Cret.]; *Plinthosella, -Z.
[Cret.]; *Phymaplectia, Hinde [Cret.]; *Rhopalospongia, Hinde [Cret.];
*Spongodiscus, Z. [Cret.]; *Stuckenbergia, Tschern. [Carb.]. [Famity
ARCHAEOSCYPHIDAE, Raut]; *Archaeoscyphia, Hinde [Cambr.]. [Faminy
CHIASTOCLONELLIDAE, Rautf]; *Chiastoclonella, Rff. [Sil.].

[Sus-TriBE OncHocLaAprnak, Rauff.]. [Famity Avtocoprpan, Rauff];
* Aulocopiwm, Oswald [Sil.]; *Dendroclonella, Rff. [Sil.].

FamILy 2. DESMANTHIDAE, Tops. With tetracrepid desmas of one

kind, either monocrepid or tetracrepid ; no microscleres; the ectosomal

megascleres monactinal, rendering the outer surface hispid. Genera—
Desmanthus, Tops. ; Monocrepidium, Tops. Famity 3. TCORALLISTIDAB,
Soll. [=Rutzomorina, Z., pars]. The desmas monocrepid and tuber-
culate. Genera—vOorallistes, O.S. [Eoc.]; Macandrewia, Gray; Dae-
dalopelta, Soll; Heterophymia, Pom.; Callipelta, Soll. Famity -4.
7PLERomrpa®, Soll. [=Mecamorrina, Z.]. The desmas monocrepid and
smooth. Genera—Pleroma, Soll.; tLyidium, O.S. [Eoe.]; *Placonella,
Hinde [Jur.]; *Megalithista, Z. [Jur.]; *Dorydesmia, Z. [Cret.] ; *Caster-
ella, Z. [Cret.]; *Holodictyon, Hinde [Cret.]; *Pachypoterion, Hinde
[Cret.]; *Heterostinia, Z. [Cret.]; *Nematrinion, Hinde [Cret.]; *JIso-
raphinia, Z. [Cret.].

Demus S—Rhabdosa, Soll. The ectosomal spicules are microrhabdi,
or modifications of them (discs). _Desmas monocrepid.

Faminy 5. NEoPELTIDAE, O.S. Ectosomal spicules monocrepid discs.
Genus—WNeopeltis, O.S. Faminy 6. SCLERITODERMIDAE, Soll. Ectosomal
spicules microrhabdi; other microscleres sigmaspires. Genera—sSclerito-
derma, O.S.; Aciculites,O.S. Famity 7. CLADOPELTIDAE, Soll. Ectosomal
spicule a monocrepid desma, highly branched in a plane parallel to the
surface ; no microscleres. Genus—Siphonidium, OS.

TRIBE 2. ANOPLIA, Soll.

No ectosomal spicules or microscleres,

Famity 8. tAzoricrpAk, Soll. [= Rarzomorina, Z., pars.]. Desmas
monocrepid. Genera—Azorica, Crtr.; Tretolophus, Soll. ; Gastrophanella,
O.S.; Setidiwm, O.S. (Fig. 28, A); Poritella, O.S.; Amphibleptula, O.S.;
Tremaulidium, O.S.; Leiodermatium, O.S.; Sympyla, Soll.; Petromica,
Tops.

[Trrpe PoEcrLocLapInipak, Rff.]

[Sup-Trine ANnomoctaprnak, Rff.]

Famity 9, tANomoctapipar, Z, Genera—f Vetulina, O.S. [Eoe.], (Fig.
29) ; *Cylindrophyma, Z. [Jur.] ; *Melonella, Z. [Jur.]; *Scytalia, Z. [Jur.
Cret.]; *Lecanella, Z. [Jur.]; *Mastosia, Z. [Jur.]. [Famity ANomo-
CLONELLIDAE, Rff.]. *Anomoclonella, Rff. [Sil]; *Pyenopegma, Rif. [Sil.]}.

150 SPONGES

[Sus-Tripe EvraxIcLaDinak, Rff.]

[Famity AstyLosponcipaE, Rff.]. *Astylospongia, Roem. [Sil];
* Caryospongia, Rff. [Sil.]; *Carpospongia, Riff. [Sil]; *Astylomanon, Roem.
[Sil] ; *Caryomanon, Hinde ; *Palaeomanon, Roem. [Sil.] ; *Protachilleum,
Z. (Sil.]; *Hospongia, Bill [Sil]. [Famriy Hryprapag, Rff.]. *Hindia,
Duncan [Sil.].

Incerti sedis. [Famity Ruizomorrna, Z. (= CORALLISTIDAE + AZORI-
CIDAE)]. Genera—*Cnemidiastrum, Z. [Jur.]; *Corallidium, Z. [Jur.];
* Hyalotragos, Z. [Jur.]; *Pyrgochonia, Z. [Jur.]; *Discostroma, Z. [Jur] ;
*Leiodorella, Z. [Jur.]; *Epistomella, Z. [Jur.]; *Platychonia, Z. [Jur];
*Bolidium, Z. [Cret.]; *Astrobolia, Z. [Cret.]; *Chonella, Z. [Cret.];
*Seliscothon, Z. [Cret.]; *Chenendepora, Lamx [Cret.]; *Verruculina, Z.
[Cret.]; *Stichophyma, Pom. [Cret.]; *Jereica, Z. [Cret.]; *Coelocorypha,
Z.[Cret.]; *Stachyspongia, Z. [Cret.]; *Pachinion, Z. [Cret.]; *Nipterella,
Hinde [Cambr.]; *Pemmatites, Dun. [Carb.]; *Kazania, Stuck [Carb.}.

GRADE II. Monaxonipa, R. and D.

Demospongiae with monaxon spicules, without admixture of
triaxon or tetraxon types.

In the classification of this most difficult and perplexing group,
which exemplifies in the fullest degree the plasticity of the Demo-
spongiae, and the frequency of adaptive and convergent evolution
in this class, we follow the classification of Topsent [26 and 28].

ORDER 1. Hadromerina, Topsent.

Monaxonida, usually of massive form, sometimes stalked or cup-shaped.
Structure compact. Skeletal framework radiate or without order, seldom
fibrous, non-reticulate. Spongin absent, or very feebly developed. Mega-
scleres monactinal or diactinal, usually of one kind only; microscleres,
when present, asters or microrhabdi, never chelae or sigmata.

Sup-Orper 1. tAcicuLina, Tops.

Megascleres diactinal.

Famiy 1. Coppatmpas, Tops. Microscleres absent, or in the form of
euasters, sometimes with the addition of streptasters. Spungosorites,
Tops.; Anisorya, Tops.; Coppatias, Soll. (incl. Astropeplus, Soll. ; and
Dorypleres, Soll.) ; Magog, Soll. ; Heméiasterella, Crtr. (= Epallax, Soll.) ;
Asteropus, Soll. Famity 2. StREPTASTERIDAE, Tops. Microscleres strept-
asters; no euasters. Genera—Amphius, Soll.; Scolopes, Soll.; Trachy-
cladus, Crtr.; Rhaphidistia, Crtr.; Spirorya, Tops.; Holoxea, Tops.
Famity 3. \7Terayrpar, Gray. Globular-or massive, with radiating
framework and differentiated ectosome; microscleres, when present,
typically euasters. Genera—fTethya, Lam. [Eoc.], (Fig. 30, A); Tethyor-
rhaphis, Laf.; Tuberella, Keller (Fig. 30, B); Trachya, Crtr.; Heteroxya,
Tops. Famiiy 4. Srytocorpyiipar, Tops. Pedunculate; framework,

tee

LS ———

j
|

SPONGES 151

radiate in the body, forms longitudinal fibres in the stalk. Genera—
Stylocordyla, W. Th. (Fig. 38); Cometella, O.S.; Halicometes, Tops.

Sup-OrDER 2. 7CLAvuLINA, Vosm.

Megascleres monactinal, usually pin-shaped tylostyles, rarely styles.

Famity 1. 7Ciiontpaz, Gray. Boring Clavulina. Genera—7Cliona,
Grant [Cret. Eoc. Mioc.]; Dotona, Crtr.; tThoosa, Hane. [Eoc.]; tAlectona,
Crtr. [Eoc.}. Famiry 2. 7SprrastReLumar, R. and D. Microscleres,
euasters, or streptasters usually accumulated to form an ectosomic crust.
Megascleres, tylostyles, or styles; occasionally diactinal. Genera—Hyme-
desmia, Bwk.; Xenospongia, Gray ; TSpirastrella, O.S. [Eoc.]; tLatrun-
culia, Boe. [Eoc.]; Sceptrintus, Tops. Famity 3. Potymastmpar, Vosm.
Without microscleres ; cortex differentiated ; skeletal framework radiate.
Genera— Polymastia, Bwk.; Trichostemma, Sars.; Rhaphidorus, Tops. ;
Proteleia, R. and D.; Tylexocladus, Tops. ; Sphaerotylus, Tops. ; Quasilina,
Norm. ; Ridleia, D.; Tentoriwm, Vosm. (= Thecaphora, O.S.), (Fig. 31).
Famity 4. 7SUBERITIDAE, Vosm. No microscleres; no differentiated cor-
tex; framework not radiate; megascleres nearly always tylostyles. Genera
—TSuberites, Ndo. [Eoc.]; Ficulina, Gray ; Laxosuberites, Tops. ; Terpios,
Duch. et Mich. ; Pseudosuberites, Tops. ; Prosuberites, Tops.; Rhizawinella,
Keller ; Semisuberites, Crtr.; Axosuberites, Tops. ; Poterion, Schlegel.

OrveR 2. +Halichondrina, Vosmaer.

Typically non-corticate ; skeleton usually reticulate; microscleres
monaxon (sigmata chelae, toxa, microrhabdi), very exceptionally polyaxon
(euasters in some Axinellidae).

Famity 1. THAPLOSCLERIDAE, Tops. (= HomorrHApPHIDAg, R. and D.
+ HETERORRHAPHIDAE, R. and D., pars), Spiculation of a simple type,
very often with diactinal megascleres alone ; microscleres, if present, never
chelae. Sup-Famity (a), FCHALININAE, O.S. Skeleton composed of fibres
of spongin enveloping diactinal megascleres; the latter often greatly
reduced in size and quantity. Microscleres usually wanting. Genera—
TOhalina, Grant [Eoc.], (Fig. 34); Pachychalina, O.S. ; Siphonochalina,
OS. ; Acervochalina, R.; Toxochalina, R.; Chalinula, O.S.; Spinosella,
Vosm. (= Tuba, Duch. et Mich.) ; Cacochalina, O.S.; Sclerochalina, OS. ;
Ceraochalina, Keller. Sup-Famity (5). 7ReNteRINAE, O.S. Skeleton of
spicules sometimes with a confused arrangement, sometimes forming a more
or less regular network. Spongin wanting or present in small quantities,
seldom enveloping the spicules completely. Genera—7Halichondria,
Flem. [Eoc.]; tReniera, Ndo. [Eoc.]; Petrosia, Vosm.; Metschnikowia,
Grimm; Pellina, O.S.; Euwmastia, O.S.; Reniochalina, Ldf.; Gellius,
Gray ; Rhaphisia, Tops. ; Menanetia, Tops.; Astromimus, Ldf.; Damiria,
Keller. Scs-Famrty (c). 7Sponeintrnan, Gray. Fresh water sponges,
for the most part similar to Renierinae. Sxrcrion a. fEUSPONGILLINAE
(=SpoNGILLINAE, Crtr.). The gemmule, so far as it is known, lacks a coat
of special spicules. Genera—7Spongilla, Lam.[Jur.],(Fig. 33); Lubomirskia,
Dyb. Sxorron 8. Meyentnaz, Vejd. The gemmule, when present, has
an envelope containing special spicules. Genera—Trochospongilla, Vejd. ;

’

152 SPONGES

TEphydatia, Lamx. (= Meyenia, Crtr.); Heteromeyenia, Potts; Tubella,
Crir.; Parmula, Crtr.; Carterius, Potts; Uruguaya, Crtr.; Potamolepis,
Marshall; Lessepsia, Keller. Sus-Famity (d). GELLIopINAE, Tops.

Skeleton formed of long thick spicular fibres, with very little spongin |

as a rule; but in Phoriospongia and Sigmatella the spicules of the
fibres are replaced by foreign bodies (arenaceous fibres) and the spongin is
abundant. Microsclere usually sigmata. Genera—Gelliodes, R.; Stylo-
trichophora, D.; Cladocroce, Tops.; Phoriospongia, Marshall; Chon-
dropsis [Crtr.], D. (=Sigmatella, Ldf.). Sus-Famiry (e). PHLOEODIC-
TYINAE, Crtr. Massive sponges with a thick cortex and fistular ap-
pendages. Framework of choanosome, a network of spicular fibres.
Microscleres, when present, sigmata. Genera—Rhizochalina, O.8.;

Oceanapia, ‘Tops. Famity 2. TPoEcILOscLERIDAE, Tops. (= Drsma- ~

CIDONIDAE, R. and D. + HeterRorwapPHipak, R. and D., pars). Megas-
cleres almost always monactinal ; microscleres various, but almost always
including chelae. Sus-Famity (a). TESPERELLINAE, R. and D. Skeletal
fibres without echinating spicules; megascleres of ectosome similar to
those of choanosome, or differing only in size. Genera—7Esperella, Vosm.
(= Esperia, Ndo.), [Eoe.]; Gomphostegia, Tops. ; tEsperiopsis, Crtr, [Eoe.],
(Fig. 37); tAmphilectus, Vosm. [Eoc.]; Stylotella, Laf.; Desmacella,
OS. ; Biemma, Gray ; Monanchora, Crtr.; tHamacantha, Gray (= Vome-
rula, O.S.), [Eoc.]; Pozziella, Tops. ; tCladorhiza, M. Sars [Eoc.]; TChon-
drocladia, W. Th. [Eoc.]; Avoniderma, R. and D.; Meliiderma, R. and D. ;
Artemisina, Vosm. ; Phelloderma, R. and D.; tDesmacidon, Bwk. [Eoe.];
Batzella, Tops. ; Homaeodictya, Ehlers; +Guittarra, Crtr. ; [Eoe.]; Sidero-
derma, R. and D.; Joyeuxia, Tops. ; Microtylotella, D.; Amphiastrella,
D. Svup-Famity ()). tDenporicrnaz, Tops. Skeletal fibres without
echinating spicules. Megascleres of ectosome, as a rule, different from
those of choanosome, and usually diactinal. Genera—Dendoryx, Gray ;
Lissodendoryx, Tops.; TtIophon, Gray [Eoe.]; Iotrochota, R.; Leptosia,
Tops.; Zedania, Gray; Trachytedania, R.; tForcepia, Crtr. [Eoc.];
TMelonanchora, Crtr. [Eoc.]; Histoderma, Crtr.; Cornulum, Crtr. ;
Yvesia, Tops. Sup-Famty (c). TEcryonrnar, Crtr. Skeletal fibres with
echinating spicules, which are usually spined. Genera—7Myzilla, O.S.
[Eoc.]; Pocillon, Tops.; Plumohalichondria, Crtr.; Stylostichon, Tops. ;
Microciona, Bwk.; Hymeraphia, Bwk.; Tylosigma, Tops.; Acheliderma
Tops.; TAcarnus, Gray [Eoc.]; Pytheas, Tops.; Hamigera, Gray ;
Spanioplon, Tops.; Clathria, O.S.; Echinoclathria, Crtr.; Agelas, Duch.
et Mich.; Ophlitaspongia, Bwk. (Fig. 82); Ectyonopsis, Crtr.; Rhaphi-
dophlus, Ehlers; Echinonema, Crtr.; Clathriodendron, Laf.; Plectispa, LAf. ;
Clathriopsamma, Ldat.; Aulena, Ldf.; Eehinodictyum, R.; Kalykenteron,
Ldf.; Fusifer, D, Sus-Famity (d). TBuBARINAE, Tops. With special
diactinal spicules, localised at the surface of attachment or forming the
axis of the sponge ; or with special megascleres (rhabdostyles). _Genera—
TPlocamia, OS. (= Dirrhopalum, R.), [Cret. Eoc.]; Suberotelites, O.S. ;
Bubaris, Gray ; Cerbaris, Tops. ; Rhabderemia, Tops. ; Hymerhabdia, Tops.
Famity 3. 7AxtneLtpar, R. and D, Megascleres typically monaetinal ;
diactinal spicules, when present, usually of subsidiary importance in
building up the skeletal framework. Microscleres wanting ‘or few in

ee id

a
,

SPONGES 153

number. Body form erect, lamellar, cup-shaped, or branched ; skeleton
fibres plumose, often more or less radiate in arrangement. Genera—
+Hymeniacidon, Bwk. [Eoc.]; Phakellia, Bwk. (Figs. 35, 36); Ciocalypta,
Bwk.; Tragosia, Gray ; Syringella, O.S.; tAginella, O.S. [Carb. Eoe.];

‘Raspailia, Ndo. ; Higginsia, Higgiy (= Dendropsis, R. and D.); Thrinaco-

phora, R.; Auletta, O.S.; Dictyonella, O.S.; Acanthella, O.S.; Halicnemia,
Bwk.; <Amorphinopsis, Crtr.; Vosmaeria, Fristedt; Sollasella, Ldf.;
Trikentrion, Ehlers; Tetranthella, Ldf.; Vibulinus, Gray (= Stelligera,
Ladf.) ; Sigmazinella, D.

ApprENDIX— Monaxonida incerti sedis. Genera—*Climacospongia,
Hinde [Sik]; *Lasiocladia, Hinde [Dev.]; *Acanthorrhaphis, Hinde
[Cret.] ; *Atractosella, Hinde [Sil.] ; *Haplistion, Young [Carb.] ; *Tricho-
spongia, Bill [Cambr.].

GRADE III. Kerarosa.

Demospongiae in which the skeleton consists of fibres of
spongin, without “‘ proper ” spicules.

The Keratosa are divided by Lendenfeld into the two orders—Mono-
ceratina, including those forms whose nearest affinity is with the Monaxo-
nida, and Hexaceratina, supposed to be descended from the Hexactinellida,
and including the Aplysillidae and the Halisarcidae (Myxospongida).

As regards the Hexaceratina so called, the theory of their affinity is
based partly upon the resemblance of the (frequently) triaxon horny
spicules of one genus (Darwinella) to the triaxon siliceous spicules of
Hexactinellids, and partly upon resemblances in their canal systems.
Since, however, nothing whatever is known of the origin and formation
of either of the two kinds of spicules in question, the assumption of their
genetic connection, however enticing as a speculation, is scarcely sufficiently
well founded for use as a systematic character; and the fact that the
Aplysillidae and Halisarcidae have thimble-shaped chambers is not con-
clusive proof of their affinity either with one another or with the
Hexactinellids.

On the other hand, Lendenfeld’s two groups undoubtedly represent a
sharp and natural cleavage of the Keratosa, after removal of the Halisar-
cidae, and we therefore retain them with an alteration of the names.
The one, characterised by a reticulate type of skeleton, we term Dictyo-
ceratina ; the other in which the skeleton is dendritic, we term Dendrocer-
atina.

OrvER 1. Dictyoceratina (= Monoceratina, Ldf.).

The spongin skeleton has the form of a network (or rather feltwork) of
anastomosing fibres.

Famity 1. Sponempar, Gray. Skeletal fibres solid; ground sub-
stance round the chambers granular; canal system aphodal. Genera—
Euspongia, Bronn (Fig. 39); Hippospongia, F.E.S.; Cacospongia, OS.;
Coscinoderma, Crtr.; Stelospongus, O.S.; Hircinia, Ndo.; Phyllospongia,
Ehlers ; Carteriospongia, Hyatt. Famity 2. Sponcenmpar, Ldf. Fibres
solid, usually with considerable quantities of foreign bodies; ground

154 SPONGES

substance round the chambers clear ; canal system eurypylous. Genera—
Spongelia, Ndo.; Velinea, Vosm.; Psammoclema, Marshall; Psammopemma,
Marshall. Famity 3. Aptysinipag, F.E.S. Fibres hollow, canal system
aphodal. Genera—Aplysina, Ndo. (Fig. 40); Luffarta (Duch. et Mich.),
OS. ; Verongia, Bwk. ; Thorecta, Laf.

OrvER 2. Dendroceratina (= Hexaceratina, Ldf., pars).

Spongin fibres dendritic, arising from a basal plate of spongin, and
not anastomosing.

Famity 4. APLYSILLIDAE, Vosm. Canal system eurypylous, with
large elongated chambers ; in Darwinella, spicules of spongin. Genera—
Aplysilla, FLES.; Darwinella, Miller; Ianthella, Gray ; Dendrilla, Laf.
(Here Hexadella, Tops. finds its nearest allies, and perhaps also
Halisarca, Duj.).

KERATOSA (? FORAMINIFERA) tncertt sedis (HAECKEL, 1889 [8)).

FaMILY—AMMOCONIDAE. “ Keratosa without spongin fibres. Pseudo-
skeleton composed of xenophya (or manifold foreign bodies), which are
disposed in the thin malthar plate of the porous tubular body. Canal
system tubular, developed on the Asconal type (similar to that of the
Asconidae).” Genera—Ammolynthus, H.; Ammosolenia, H.; Ammo-
conia, H.; Prophysema, H. Famity—Psamminipag, Ldf. “ Keratosa
without spongin fibres. Pseudo-skeleton composed of xenophya. . .
which are cemented together and enclosed by the transparent maltha.
Canal system vesicular, developed on the Leuconal type (similar to that
of the Spongeliidae).” Genera—Psammina, H.; Holopsamma, Crtr. ;
Psammopemma, Marshall. Famity—Srannomipar, H. “ Keratosa with
a fibrillar spongin skeleton, composed of thin, simple, or branched spongin
fibrillae, never anastomosing or reticulated. Pseudo-skeleton composed

of xenophya . . . which are crowded in the transparent maltha, never
in the homogeneous fibrillae. Canal system vesicular... on the
Leuconal type... .” Genera—Stannophyllum, H.; Stannariwm, H. ;

Stannoma, H.
GRADE IV. Myxosponaipa, Soll.
Sponges devoid of a skeleton in any form.

Famity 1. OscareLuipar, Ldf. With spherical ciliated chambers.
Genus—Oscarella, Vosm. (Fig. 41). Famriy 2. Hartsarcrpar, O.S. With
elongated, sack-like ciliated chambers. Genera—Halisarca, Duj.; Bajulus,
Ldf. ; Hexadella, Tops.

APPENDIX TO CLASSIFICATION.

Under the names Octactinellida and Heteractinellida, Hinde (1887)
has described two groups of Palaeozoic sponges, each with a very aberrant
type of spicule, which cannot be brought either under the triaxon or
tetraxon type.

In the Octactinellida, represented by the single genus Astraeospongia

SPONGES 155

_of Roemer, the typical spicule (megasclere) has eight rays (Fig. 95, A). Six
of the rays are placed in one plane, which may be termed horizontal,
and in which they radiate out A
at equal angles of 60° from a
common centre. The two re-
maining rays radiate from the
centre in opposite directions,
forming a vertical axis which
cuts the horizontal plane at right
angles. Spicules of this normal
type are, however, less frequent ,

than a modification in which rlaeel sik ;

the two vertical rays are reduced ap sog exten Chttoe es recat

to nodules or are absent alto-

gether, thus producing a flat, six-rayed star (Fig. 95, B).

In the Heteractinellida the typical spicule is a huge euaster with from
six to thirty rays, coming off from a common centre at different angles
(Fig. 96, A). This type form is again less common than some of its
modifications. By the rays being placed nearly in one plane, in which
they are confluent at their bases, a disc-like star is produced (Fig. 96, B),

LB.

Fic. 96,

Spicules of Heteractinellida. A, typical polyactine; B, rosette-like form; C, D, Z, nail-
like forms—C and # in profile, D from below. (After Hinde.)

_ which may further have three or four rays coming off at right angles, or
nearly so, from one surface of the disc. A characteristic modification of
this type produces nail-like spicules (Fig. 96, C, D, EZ), in which there is a
dise with six to nine rays projecting horizontally, from the centre of which

a stout ray is given off in a vertical direction. The rays may be equal or

13

156 SPONGES

unequal in size, and may be straight or tapering, blunt or sharp, smooth
or with warts on one surface.

Should these observations be confirmed, it is evident that we have
here two groups of equal systematic importance with the Hexactinellids
and Demospongiae, which have not left descendants persisting to our
time. In addition, therefore, to the three classes now existing, we should
have to add the following :—

Crass 4. *OcTACTINELLIDA, Hinde.

With octactinal megascleres). Genus—Astraeospongia, Roemer [Sil.
Dey. |.
Crass 5. *HETERACTINELLIDA, Hinde.

With polyactinal megascleres. Tholiasterella, Hinde [Carb.]; Aster-
actinella, Hinde [Carb.].

V. THe DISTRIBUTION OF SPONGES IN SPACE AND TIME. «

The orders and families, and even as a rule the genera, of the
Porifera are cosmopolitan in their geographical distribution. Their
occurrence in any quarter of the globe is subject only to the re-
strictions imposed by the peculiar conditions necessary for their
existence in each case, such as, for instance, their bathymetrical
distribution, presently to be discussed. Even the freshwater
sponges, in spite of the discontinuous nature of their habitat, seem
to occur in the lakes and rivers of all countries. In the latter case,
the gemmules afford an important means of distribution on account
of their resistance to external vicissitudes and the ease with which,
in many cases, they can be transported by winds. In marine
sponges the larvae are probably often carried great distances by
currents, and in some cases gemmules, or other non-sexual repro-
ductive bodies, may also play a part in their dispersal.

Although no group or family of sponges appears to be limited entirely
to any particular region, yet many are found more abundantly in certain
regions of the globe than elsewhere, and may be said to characterise these
areas. Thus in the Hexactinellids a far larger number of species are re-
corded from the Pacific than from the Atlantic or Indian Oceans ; this is
true both of Lyssacina and Dictyonina; but while in the case of the
former the south temperate zone is the richest and the north temperate zone
the poorest in species, the Dictyonina reach their richest development in
the tropical zone (Schulze). In the Demospongiae, the Keratosa, a group
to which warm and shallow waters seem to be most congenial, are most
abundant in southern and antarctic regions (Lendenfeld). The Monax-
onida, though a widely spread and very cosmopolitan group, are most
abundant in the Indo-Australian region, a fact true especially of the very
populous sub-families of the Chalininae and Ectyoninae. Tedania and its

SPONGES 157

' allies, on the other hand, are more characteristic of the Patagonian region
(Ridley and Dendy) ; while the higher systematic groups of sponges have
the widest possible distribution, the range of individual species is often
very restricted, though certain forms may be of widespread occurrence,
Instances of the latter are seen in some generalised forms, such as
Halichondria panicea, Suberites carnosus, and many others amongst
Monaxonida. The species inhabiting deep water occur, as a rule, over
wider areas than those restricted to the shore-line.

The classes of Porifera are better characterised by their bathy-
metrical distribution than by their geographical habitat. Speaking
generally, it may be said that the Calcarea and Monaxonida are
shore forms, inhabiting the highest littoral zone, and flourishing
between, tide marks; the Choristida, amongst Tetractinellids, and
the Keratosa are most abundant just below tide marks, down to
about 50 fathoms; the Lithistida characterise a slightly deeper
belt, from 100 to 150 fathoms; while the Hexactinellids are
typical inhabitants of deep water, the Dictyonina occurring in
moderate depths, near the coast, and the Lyssacina in the abyssal
regions far from the coast. In every case, however, the limits of
these generalisations are overstepped by particular species. Thus
Thenea muricata (Choristida) has been recorded from 1913 fathoms
(Wright), and many Monaxonida have spread down to great
depths, as, for example, Cladorhiza longipmna (R. and D.) from
3000 fathoms. It has already been pointed out as an interesting
fact that the influence of an abyssal habitat upon these character-
istic littoral forms, is to cause them to exchange their irregular
body form for a symmetrical mode of growth, which is clearly
secondary and newly acquired.

The geological record of the Porifera is largely dependent, as
might have been expected, upon the nature of the skeleton. In
each group we find those forms especially represented by fossils in
which a rigid and coherent framework has been evolved; for
instance, amongst Calcarea, the Pharetronidae; amongst Hex-
actinellids, those with a dictyonal framework; and amongst
Demospongiae, the Lithistida. Since in each case these are the

_ least primitive examples of the groups to which they belong,
_ Palaeontology affords us but little help in unravelling the phylo-
_ genetic connections of the groups of Porifera. We know nothing
of the past history or distribution of the more primitive groups,
such as the Ascons or the Carnosa. The most ancient sponge
known, however, namely, Protospongia from the Cambrian, is
characterised by triaxon spicules of the most primitive and un-
modified type, and the early Palaeozoic forms classed by Hinde as
* Octactinellida and Heteractinellida perhaps represent offshoots from
a very early and primitive stock, which have not left descendants
persisting to the present day. On the other hand, a remarkable

158 SPONGES

feature of the forms mentioned is the relatively very large size of
their spicules, which is probably not a primitive characteristic.

In general the Palaeontological record shows the extreme
antiquity of the chief types of sponges, and their wide occurrence
at all periods of the world’s history, but is far from supplying links
to connect the branches of the phylogenetic tree. We notice
further that the forms most abundant as fossils are those which are
now characteristic of deep water; but it is not necessarily to be
inferred from this that the fossil forms were also inhabitants of the
abyss.

VI. Tue AFFINITIES AND PHYLOGENY OF SPONGES.

The theoretical questions which are suggested by a study of the
group of sponges, fall naturally under two headings. First, we
may consider sponges in general in their relation to other classes
of living beings. We are then confronted with the question—
what are the affinities of the simple and primitive sponge individual
with other animals? Secondly we have to deal with those questions
of which the range is limited and restricted within the phylum
itselfi—that is to say, the evolution of sponges in general, and the
pedigree and phylogenetic relations of the principal groups.

(a) Position of Sponges in the Animal Kingdom.—The most con-
flicting opinions have been, and still are, held upon this point. Up
to the middle of the present century it was still disputed whether
sponges were animals or plants. The discovery of cilia in them by
Dujardin and Dobie was considered a decisive proof of their animal
nature, but their systematic position still remained a matter of
controversy. By Dujardin, Lieberkiihn, Carter, James-Clark, and
Savile-Kent, they were regarded as Protozoa, but with the progress
of knowledge such a view has become incompatible with any
rational definition that could be framed to separate the Protozoa
from the higher animals. Modern authors are divided, in the first
place, as to whether the sponges are to be regarded as Enterozoa,
or as an independent phylum, distinct both from the Protozoa and
from the Enterozoa (Biitschli, Sollas, and formerly Delage [2}).
Those who regard them as Enterozoa are further divided in opinion,
especially as regards the homologies of the two primary germ
layers. Balfour, whom at the present time Maas and Delage
follow, considered them as composed of ectoderm and endoderm,
homologous with the similarly named layers in Coelentera, but in
sponges reversed in position at the metamorphosis ; Heider, Gitte,
and Néldeke also consider that sponges have nothing in common
above the gastrula stage, and the two latter believe that the sponge
body is developed from the endoderm alone. On the other hand,
Leuckart and Haeckel regard sponges as true Coelentera, composed
of the same two primary germ layers, and built up on the same

4

aie

SPONGES 159

architectural plan ; and Schulze, whom most authors follow, places
the Porifera as a subdivision of the Coelentera, marked off by the
possession of a distinct mesoderm, and the absence of nematocysts
or tentacles from the remainder of the Coelentera or Cnidaria.

We have then three views to discuss, each of which is based
upon a distinct theory of sponge genealogy: first, that sponges are
descended from a Protozoon ancestor distinct from that of other
Metazoa ; secondly, that they have a common ancestry with other
Metazoa, as far as the diploblastic stage of development, and are
therefore composed of the same two primary germ layers, but that
after this stage they have proceeded along a distinct and in-
dependent line of evolution ; and thirdly, that they have a common
ancestry with the Coelentera, both being descended from a
gastrula-like progenitor with a body wall composed of ectoderm
externally and endoderm internally. The sponges would then be
a modification of the Coelenterate ancestor in one direction, the
Cnidaria in another.

In considering these views we may take the last first, as being
the most easy to refute, although still that most generally adopted.
The result of recent embryological work has been to completely
undermine the Coelenterate theory of sponge affinities, by demon-
strating that at the metamorphosis the germinal layers become
reversed in position, in a manner not suspected by those who
first put forward this view. The Coelenterate theory assumes
that sponges are composed developmentally of the same two
germinal layers as the Coelentera, which also have the same archi-
tectural relations in the adult. The reversal of the layers makes it
impossible, however, to extend the comparison to both the larvae
and the adults. For if the comparison starts from the larvae, then
the adult sponges are composed of endoderm externally and ecto-
derm internally. If, on the other hand, the adults are compared,
and their constituent layers homologised, then the larvae of sponges
are quite anomalous, consisting of an endoderm surrounding com-
pletely, or very largely, the ectoderm. Since the Coelenterate
theory has become quite untenable at the present day, at least in a
strict phylogenetic sense, we have to choose between one of the two
remaining views: either that sponges have a separate descent from
the Protozoa, i.e. from the Choanoflagellata, an idea which has sug-
gested the term Parazoa, applied to them by Sollas; or that they
are Enterozoa, in which the two primary germ layers have become
reversed in position, a view expressed in the name Lnantioderma s.
Enantiozoa* coined for them by Delage (1898 [3]).?

1 From the Greek évayrios, inside out.

2 The theory of Gétte and Néldeke that sponges are developed from the endo-
derm alone, was founded on mistaken observations upon the development of
Spongilla, and at the present day is lacking in any basis of fact.

160 SPONGES

To obtain constructive evidence of a convincing nature in favour
of either of these views is a matter of extreme difficulty, if not im-
possible. On the side of the Choanoflagellate ancestry we may
urge the invariable presence of collar cells and their remarkable
resemblance to Choanoflagellata (see above, p. 53). The theory of
Enterozoic affinities of sponges, on the other hand, is based upon
their sexual reproduction and the resemblance of the early develop-
mental stages, culminating in a two-layered, planula-like larva, to
those of other Metazoa. The latter theory seems, therefore, at
first sight, to stand upon a wider basis than the former, but a closer
scrutiny leads to the conclusion that the supposed Enterozoic char-
acters of sponges are far from being of a very diagnostic nature.
In the first place, sexual reproduction by means of ova and sper-—
matozoa is of widespread occurrence in plants as well as animals.
Secondly, the type of segmentation seen in any ovum depends, as
is well known, largely on its constitution, and in so far may admit
of explanation by purely physical laws. And finally, as regards
the germinal layers, the subsequent fate of these layers in the
sponge embryo makes it very difficult to homologise them with
those of other Metazoa.

While, therefore, the characters that connect the sponges with
the Enterozoa are of rather a shadowy and vague nature, the pos-
session of collar cells stands out, at present, as a sharply defined and
very diagnostic feature in their organisation which links them to the
Choanoflagellata, and this view receives indirect support from the
many anomalies of sponge development which make it very diffi-
cult to bring them into line with other animals.

If from the basis of a Choanoflagellate ancestry we try to reconstruct the
past history and evolution of the sponge phylum by the help of the stages
seen in embryology, we find the simplest condition typified in the larvae
of Ascons. The larva of Clathrina before immigration has commenced
may be regarded as a Protozoon colony composed of nutritive zooids,
together with a small number specialised for reproduction (cf. Figs.
57, 1, and 58, 1). Such colonies are seen in the Volvocineae and in
Proterospongia (Savile-Kent). In the sponge ancestor the nutritive
zooids were doubtless provided each with a collar and flagellum ;
in the sponge larva the flagellated cells serve during the free swimming
stage only for locomotion, and their nutritive function is in abeyance,
hence the collar is not developed on them until after the metamorphosis.
As time went ona third class of cell was developed by modification of the
nutritive zooids, as occurs in all sponge larvae. These new elements may
have had at first a digestive and distributive function, or they may have
been skeletogenous, or finally, they may have simply been a modified form
of flagellated cell, as exemplified in the larva of Oscarella, and specialised
perhaps for locomotion rather than nutrition. Im any case the non-
reproductive zooids, at first all alike, became subdivided into a specially
nutritive set, retaining the primitive characters, and another set specialised

- "

SPONGES 161

in other directions. The former remained at the surface, the latter tended
to migrate into the interior.

Next followed the very obscure portion of the phylogenetic history in
which the ancestor became fixed, and underwent changes which resulted
in the nutritive collar cells becoming placed in the interior to form the
gastral layer, while the other cells came to surround them and form the
dermal layer. Although these two events, the fixation and the reversal
of the layers, doubtless stand in close relation to one another, it is difficult
to say which preceded the other, or to attempt to follow this period of the
evolution in detail. It is represented in ontogeny by the metamorphosis,
which, like all similar stages throughout the animal kingdom, evidently
represents a large and important series of phylogenetic stages compressed
into a very short time, and much modified in nature. When once the
metamorphosis is past, the subsequent pupal stages are not difficult to
interpret. It has already been pointed out that the flattened pupa formed by
metamorphosis of the larva of Clathrinaw may be regarded as a very simple
type of sponge in a state of extreme contraction. Its further histogenetic
development, which in ontogeny takes place in the contracted condition,
or during the gradual process of expansion, gives us a clue to understand-
ing how in phylogeny the calcareous Olynthus was evolved from the simple
Protolynthus, the ancestor of all sponges.

The Choanoflagellate theory of sponge ancestry may be said therefore
to afford a simple interpretation of all stages of the embryology, with the
exception of the metamorphosis, a portion of their life-history of which the
significance still remains very obscure. We may console ourselves, how-
ever, with the thought that the metamorphosis is equally, if not more,
difficult to interpret from a phylogenetic point of view on the Enterozoic
theory, and that it becomes absolutely unintelligible from any point of
view if the Coelenterate theory be adopted.

(b) The Phylogeny of Sponges.—Three main lines of descent and
evolution can be recognised in sponges generally, represented by the
Calcarea, the Hexactinellida, and the Demospongiae respectively.
In the former we have a very distinct stock, with no transitions to
other forms. The Hexactinellids, on the other hand, have in the
siliceous nature of their skeleton a feature which links them with
the Demospongiae, but it is open to discussion whether this peculi-
arity is inherited by both from a common ancestor with a siliceous
skeleton, or has been independently acquired.

Haeckel believes the common ancestor of all sponges to have been a
form which inhabited the deep sea, and was provided with a pseudo-
skeleton of foreign bodies, consisting chiefly of the skeletons of Radiolaria,
Foraminifera, and other pelagic animals which were continually showering
down uponit. This primitive sponge next acquired the power of dissolv-
ing the siliceous and calcareous matter which it took up, and depositing
the mineral substance anew in the form of spicules in the tissues. Some
sponges, which lived in Globigerina ooze, acquired in this way a calcareous
skeleton ; others living in Radiolarian ooze acquired a siliceous skeleton.

162 : SPONGES

The consequence was the evolution of sponges along two lines, characterised
each by the material composing the supporting framework of the body.

Whatever may have been the first origin of sponge skeletons, that of
the siliceous sponges shows two distinct lines of evolution, In Hex-
actinellids the starting-point was a form of simple structure with triaxon
spicules. The Demospongiae may be referred back, similarly, to a
primitive Rhagon form with tetraxon spicules. In both cases the form of
spicule may be explained as an adaptation to the canal system and
architecture of the primitive sponge (Schulze). The primitive hexactines
of the triaxon type are of the form best suited to the elongate, thimble-
shaped chambers, and the loose trabecular structure of a simple Hexac-
tinellid, while the tetraxon spicule fits the closely packed rounded chambers
and the denser texture of the body wall of a Plakina-like ancestor. The
question arises whether the two types of body structure were evolved
before or after the sponge had acquired a siliceous skeleton of some kind.
It is possible that a remote, ancestral Myxosponge, with flagellated chambers
opening into a gastral cavity, secreted siliceous concretions and sclerites,
which became spicules of a more or less irregular polyaxon form, and that,
as the canal system of this sponge developed in one or the other direction,
the polyaxon spicules became adapted to its structure and gradually settled
down, so to speak, into the two types represented by the triaxon and
tetraxon megascleres respectively. If this be so, we might expect to find
other lines of sponge descent, in which the primitive polyaxon sclerite had
given rise to other types of spicule, and such forms are perhaps repre-
sented by the Palaeozoic sponges placed by Hinde in the two groups named
by him Octactinellida and Heteractinellida. On this view we may
recognise a class Silicea, of equal phylogenetic value with the Calcarea,
and divisible into two branches, the Triaxonia or Hexactinellids and the
Tetraxonia or Demospongiae. It remains to consider briefly how the
various groups of non-calcareous sponges are to be distributed along these
two lines of descent.

The most primitive Demospongiae are to be found in the order
Carnosa, and particularly in the family Plakinidae. Plakina mono-
lopha is but little advanced beyond the primitive Rhagon type,
and its spicules are of small size, and for the most part of simple
tetraxon form. The progressive complications found in other
species of the same genus and in other genera of the Carnosa lead on
to the typical Tetractinellids with a well-developed cortex, and with
tetractines showing a corresponding differentiation between three
tangential rays situated in the cortex and an enlarged ray
directed radially ; in other words, with triaenes. The Lithistida
are to be considered as developed from primitive Tetractinellids, in
which some of the tetractines become encrusted and enveloped by
secondary deposits of silica to form the desma, with consequent
atrophy and reduction of the primitively tetraxon crepis, as well of
the free triaenes ; all stages of this evolution being still preserved in
different members of the group.

——

g

SPONGES 163

From a corticate Choristid with a radiate skeleton the step to
Tethya and allied forms is not great. The triaenes are replaced by
monaxons, orientated in a similar manner to the rhabdomes of the
triaenes, and doubtless corresponding to them. By reduction of the
tetraxons the sponge has now become a Monaxonid, the starting-point
of a new evolutionary series. While many Monaxonida, especially of
the order Hadromerina, differ little from typical Choristida except
in the absence of tetraxon spicules, others by reduction or dis-
appearance of the cortex, absence of the characteristic asters
amongst the microscleres, shortening and diminution of the monaxon
megascleres, and loss of their radiate arrangement, acquire a type
of structure which in the end terms of the series is of a very
distinct character. While the Hadromerina retain, as an order,
many marks of Tetractinellid affinities, all traces of the latter
become obliterated more or less completely in the Halichondrina,
with their reticulate type of skeleton, held together very often by
an element which was absent or very inconspicuous in the Hadro-

-merina and Tetraxonida, namely, spongin.

The Halichondrina in their turn are the starting-point of an
evolution in yet another direction, in which the spicules become
gradually lost and replaced by spongin, which ultimately comes to
make up the whole skeleton. The transitions between the
Halichondrina and Keratosa are numerous and gradual, and, as
already pointed out above (p. 139), the evolution of a so-called horny
sponge has probably taken place in more than one family of
Halichondrina, and perhaps even more than once within the limits
of the same family. So inseparable are the Keratosa, or rather the
Dictyoceratina, from the Halichondrina in a natural classification
that it has been proposed by Vosmaer and others to unite them in
one group Cornacuspongiae, and so separate them from the other
Demospongiae which, in their turn, are to be united in one class
Spiculispongiae, comprising the Tetraxonida and Hadromerina. This
arrangement, however, is open to just the same objections as that
which it is intended to replace, namely, that it introduces sharp
cleavages where none naturally exist, and for practical purposes it
is less convenient than the frankly artificial classification into
Tetraxonida, Monaxonida, and Keratosa.

It is seen that from the most primitive Tetraxonida to the typical
horny sponges we find an wninterrupted series of gradations, and though
it might be possible to link the various forms together along lines different
from those which have been traced above, it is not possible to introduce sharp
distinctions between them. On the other hand, in the Keratosa themselves
we come perhaps for the first time to a discontinuity in the chain of forms.
The two orders of the Keratosa seem to have little in common except the
material of the skeleton, and Lendenfeld has sought to bring the Dendro-
ceratina near to the Hexactinellids, on the supposition that they represent

164 SPONGES |

an evolutionary series in which the siliceous material of the triaxon
spicule has become replaced by spongin, giving rise to horny spicules,
combined with a dendritic horny skeleton, as in Darwinella. Further steps
in this direction would lead to loss of the horny spicules, as seen in the other
Dendroceratina ; while finally, the Halisarcidae are supposed to arise by
complete suppression of the entire horny skeleton. However interesting
and suggestive this theory may be, it cannot be said, in the present state
of our knowledge, to be more than a guess. It is not clear how the
alleged Hexactinellid ancestor acquired its dendritic horny skeleton, and
it is just as easy to take the Halisarcidae as the starting-point of the series,
to derive the dendritic skeleton from an upgrowth of a basal plate of
spongin, and to regard the horny spicules, present in a single genus, as
originating by discontinuous secretion of spongin in a form already
provided with a dendritic skeleton.

While, in the Myxospongida, the affinities of the Halisarcidae
are uncertain and in need of further elucidation, the Oscarellidae, on
the other hand, seem to stand very near the Plakinidae. Oscarella
scarcely differs from the simpler species of Plakina except in the
absence of any skeleton, and there is no evidence whatever that it
is degenerate in this respect. Oscarella may be regarded therefore as
in many respects the most primitive Demosponge, representing more
than any other the simple Rhagon ancestor of the group. Since,
on the other hand, it seems to have little affinity with any
Hexactinellids, it points to the siliceous skeleton having been
independently evolved in the ancestors of the Triaxonia and
Tetraxonia respectively.

The Hexactinellids, unlike the Demospongiae, are a compact and
homogeneous group of very uniform structure, presenting no special
phylogenetic difficulties. The starting-point is a simple Rhagon-
like form, as described above, from which all the known types are
easily derived.

The phylogeny of the Calcarea has already been briefly dis-
cussed, and it has been seen that the two families of the Homocoela
represent the two main divergent branches of the genealogical tree.
It is not possible at present, however, to trace these branches upwards
through the grade Heterocoela, until the latter have been further
studied from this. point of view.

LITERATURE OF THE PORIFERA.

The following list of references comprises, in the first place, those memoirs or
monographs which deal with some sponge question or group in a comprehensive
manner, and contain exhaustive references to the literature ; and, in the second
place, works of very recent date, which supplement and extend the larger
treatises. Many important memoirs are, therefore, not cited separately, as they
are to be found quoted by all authors; such as, for instance, in morphology,
histology, and development, the classical memoirs of Carter, Lieberkiihn, —

a

LITERATURE OF THE PORIFERA 165

Schulze, Metschnikoff, Barrois, Keller, Schmidt, and many others ; in physiology,
Lieberkiihn, Metschnikoff, Lendenfeld, etc.; for the classification and system
Gray, Bowerbank, Schmidt, Topsent, Lendenfeld, and Breitfuss; and in
palaeontology, the works of Hinde and Zittel. Full bibliographies are given
by Vosmaer [29 and 30], Lendenfeld [9], Rauff [19], and Weltner [31], and
references to recent literature will be found in the Zoological Record, published
by the Zoological Society of London, and in the Bibliographia Zoologica, edited
by Victor Carus, and published with the Zoologischer Anzeiger (Leipzig, W.
Engelmann),

1, Bidder. The Skeleton and Classification of Calcareous Sponges. (Proc.
Roy. Soc., 64, 1898, pp. 61-76.)

2. Delage. Embryogénie des Eponges. (Arch. Zool. Exp. (2), x. (1892), pp.
345-498, pls. xiv. -xxi.)

3. —— Sur la place des Spongiaires dans la Classification. (C. R. Ac. Sci.
Paris, vol. exxvi. (1898), pp. 545-548.)

. Dendy. Monograph of the Victorian Sponges I. (Tr. Roy. Soc. Victoria,
III. (1891), pp. 1-81, xi. pls.)
5. Studies on the Comparative Anatomy of Sponges, V. Calcarea Hetero-

cela. (Quart. Journ. Micr. Sci., N.S. vol. xxxv. (1893), pp. 159-257, pls.
X.-Xiv.)

6. Déderlein. Ueber die Lithonine. (Zool. Jahrb., Abth. f. Syst. ete., x.

_ (1897), pp. 15-32, pls. ii.-vi.)

7. Haeckel. Die Kalkschwimme. (3 vols. Berlin, 1872.)

— 8. —— Deep Sea Keratosa. (Challenger Reports, Zool., vol. xxxii. 1869.)

9. Lendenfeld. Monograph of the Horny Sponges. (London, 1889.)

10. Loisel. Contribution 4 l’histo-physiologie des éponges. (Journ. de l’anat.
et de la physiol., xxxiv. (1898), pp. 1-43 and 186-234, pls. i. and v.)

11. Maas. Embryonal-Entwickelung, etc., der Cornacuspongien. (Zool. Jahrb.,
Abth. f. Anat., ete., vil. pp. 331-448, pls. xix-xxiii.)

12. —-_ Ueber die erste Differenzierung von Generations und Somazellen bei
den Spongien. (Verh. deutsch. Zool. Ges., 1893, pp. 27-35.)

13. Die Keimbliitter der Spongien, etc. (Zeitschr. f. w. Zool., lxiii. (1898),
pp. 665-679, pl. xli.)

14. Die Entwickelung der Spongien. (Zool. Centralblatt V., 1898,
pp. 581-599.)

15. Ueber Reifung und Befruchtung bei Spongien. (Anat. Anzeiger,

1899.)

—16. Minchin. The Position of Sponges in the Animal Kingdom, (Science
Progress, N.S. I. (1897), pp. 426-460. )

17. —— Materials for a Monograph of the Ascons I. (Quart. Journ. Micr.
Sci., N.S. xl., 1898, pp. 469-587, pls. xxxviii.-xlii.)

18. Foléjaeff. Calcarea. (Challenger Reports, Zool., vol. viii., 1883.)

19. Rauff. Paleospongiologie. (Paleontographica, xl. pp. 1-346, pls. i.-xvii. ;
and xli. pp. 223-272, pls. xx.-xxvi.)

—20. Ridley and Dendy. Monaxonida. (Challenger Reports, Zool., vol. xx.)

_ 21. Schulze. Hexactinellida. (Challenger Reports, Zool., vol. xxi.)

22. —— Symmetrieverhiiltnisse bei Hexactinelliden-Nadeln. (Verh. deutsch.
Zool. Ges., 1897, pp. 35-37.)
23. —— Zur Histologie der Hexactinelliden. (Sitzber. Akad. Wiss., Berlin,

xiv., 1899, pp. 198-209.)

166 LITERATURE OF THE PORIFERA —

— 24. Schulze. Amerikanische Hexactinelliden, ete. (Jena, Gustav Fischer, 1899,
text and atlas.)
__25. Sollas. Tetractinellida. (Challenger Reports, Zool., vol. xxv.)
26. Topsent. Classification des Halichondrina. (Mém. Soc. Zool. France, viii.,
1894, pp. 5-22.) :
_~ 27. —— Etude monographique des spongiaires de France. I. Tetractinellida,
II. Carnosa. (Arch. Zool. Exp. (3), ii. 1894, pp. 259-400, pls. xi.-xvi.,
and (3), iii, 1895, pp. 493-590, pls. xxi.-xxiii.)

28. —— Classification des Hadromerina. (Arch. Zool. Exp. (3), vi. 1898, pp.
91-116.)

29. Vosmaer. Spongien. (Bronn’s Thierreich, ii. 1887.)

30. —— and Pekelharing. Observations on Sponges. (Verl. d. k. Acad. v.

Wet., Amsterdam, (2), vi. 3.)

31. Weltner. Spongillidenstudien i., ii., iii, (Arch. f. Naturgesch, 1893, pp.
209-284, pls. viii., ix., and 1895, pp. 114-144.)

32. Zittel. Palaeozoologie, Bd. I. (Munich and Leipzig, 1876-1880.)

33. Zykof. Entwickelung der Gemmulii bei Ephydatia fluviatilis. (Bull. Soc. —
Imp. Nat., Moscow, 1892, pp. 1-16, pls. i., ii.)

Addendum to Bibliography—

34. Evans. The Structure and Metamorphosis of the Larva of Spongil/a lacustris.
(Quart. Journ. Mier. Sci., n.s. 42, 1899, pp. 363-476, pls. 35-41.)

ABBREVIATIONS OF AUTHORS’ NAMES.

Bill., Billings. Boc., de Bocage. Bwk., Bowerbank. Crtr., Carter. D., Dendy. —
Defr., Defrance. Did., Diderlein. d’Orb., d’Orbigny. Duch. et Mich., Duch-
assaing et Michelotti. Duj., Dujardin. Dun., Dunikowski. Dyb., Dybowski.
Eichw., Eichwald. Et., Etallon. Fabr., Fabricius. F. E. S., F. EB. Schulze. Flem.,
Fleming. From., Fromentel. Goldf., Goldfuss. H., Haeckel. Han., Hanitsch.
Hane., Hancock. Iij., Iijima. J. Cl., James-Clark. Johnst., Johnston. L.,
Linnaeus. Lam., Lamarck. Lamx., Lamouroux. Ldf., Lendenfeld. Mant.,
Mantell. Mich., Michelin. Mont., Montagu. Murch., Murchison. Ndo.,
Nardo. Norm., Norman. O. S., Oscar Schmidt. Pall., Pallas. Park.,
Parkinson. Peng., Pengelly. Pol., Poléjaeff. Pom., Pomel. Qst., Quenstedt.
k., Ridley. R. and D., Ridley and Dendy. Rifl., Rauff. Roem., Roemer. Rss.,
Reuss. S. K., Savile- Kent. Schliit., Sciiliiter. Soll., Sollas. Steinm., —
Steinmann. Stew., Stewart. Stuck., Stuckenberg. Stutchb., Stutchbury. ;
Tops., Zopsent. Tschern., Tschernyschew. Vejd., Vejdowsky. Vosm., Vosmaer.
Wale., Walcott, Welt., Weltner. W. Th., Wyville-Thomson. Z., Zittel.

ADDENDUM.

Since the above chapter was in print a remarkable type of calcareous
sponge has been discovered by Dr. Willey. It was found by him
growing on dead coral in Sandal Bay, Lifa, Loyalty Islands (Western
Pacific). A description of this organism under the name Astroselera
Willeyana will shortly be published in Dr. Willey’s Zoological Results,
Part IV., by Mr. J. J. Lister, to whose kindness we are indebted for the
following description, compiled from advance proof-sheets of his work, as
well as for the two figures here given (Fig. 97, A and B),

The four specimens obtained of this sponge were cylindrical in form, |

ADDENDUM TO SPONGES 167

about 10 mm. in height by 5 mm. in breadth. The openings of the
canal system are confined to the upper surface (Fig. 97, A; ef. Tentoriwm,
Fig. 31).

The skeleton of Astrosclera is composed, not of spicules, which are
entirely wanting, but of calcareous spherules, which arise in cells of the
dermal layer near the upper surface. Each spherule is deposited within
a single cell, and is from the first composed of radially arranged crystalline
fibres. Its form is at first spherical, but by further increase in size
adjacent spherules come into contact, and the interspaces between them
become completely filled in by continued deposition of the calcareous

Astrosclera Willeyana, Lister. <A, the sponge magnified about three diameters ; p.s., upper
surface carrying the openings of the canal system; b, base of attachment. JB, section of the
Skeleton ; sph., spherules ; ¢, canals. (Drawings by Mr. J. J. Lister.)

substance, to the exclusion finally of the soft parts. The spherules thus
acquire a polyhedral form (Fig. 97, B, sph.), and by their union build up
a solid calcareous skeleton without any admixture of soft parts, but
traversed by canals in which are lodged the soft tissues and the canal
system of the sponge (Fig. 97, b,c). In the basal (older) part of the
sponge the canals became obliterated, apparently by extension inwards of
the spherules forming their wall; just as in pedunculate sponges the
canal system is wanting in the stalk,

The spherules are composed of aragonite, and contain an organic
basis which has the same staining reactions as that of the spicules of
Calcarea.

The canal system is of a leuconoid type with small spherical ciliated
chambers opening into branched canals. There is no large central
gastral cavity, but a number of excurrent canals [which perhaps represent
gastral cavities reduced in size] run vertically upwards to open on the
upper surface, alternating with incurrent canals similar in appearance and
arrangement. Some ova and larvae were observed, the latter apparently
of a parenchymula type.

The affinities of this curious organism are very doubtful. It is un-
questionably a sponge, and the material of its skeleton is carbonate of

168 ADDENDUM TO SPONGES

lime, but the fact that it is in the form of aragonite may indicate that
Astroselera is genetically distinct from the true Calcarea, in which the
skeleton is invariably calcite, On the other hand, it is possible that the
spherules have in the course of phylogeny replaced a skeleton of calcite —
spicules originally present. In some Pharetrones a similar skeleton of —
spherules is known (Zittel), but in such cases the spherules are generally
regarded as a secondary formation due to recrystallisation of the lime —
during fossilisation. ‘ Under these circumstances it seems. better to class —
Astrosclera as the type of a new family Astroscleridae, possibly allied to —
the Pharetrones, but certainly without close affinity with any other known
group of sponges” (Lister).

A larger specimen of the same genus and probably of the same species
of sponge has recently (November 1899) been detected by Mr. Kirk- —
patrick of the British Museum (Natural History) in a collection of |
marine organisms dredged at Funafuti (Gilbert Islands). :

INDEX

To names of Classes, Orders, Sub-Orders, and Genera ; to technical terms ; and to
names of Authors discussed in the text.

Acanthascinae,
and genera, 122
Acanthascus, 122
Acanthactinella, 123
Acanthella, 153
Acanthin, 43
Acanthodictya, 123
Acanthometridae, 43
Acanthorrhaphis, 153
Acanthosaccus, 122
Acarnus, 138, 152
acerate spicules, 101
Acervochalina, 151
Acheliderma, 152
Aciculina, 78, 146
— diagnosis and classifica-
tion, 150
Aciculites, 149
acrepid, 135
actinoblast, 40, 107
aesthacytes, 47
Agelas, 152
alate spicules, 102
Alectona, 151
Algol, 148
Ammoconia, 154
Ammoconidae,
and genera, 154
Ammolynthus, 154
Ammosolenia, 154
amoebocytes, 28, 58, 62,
12; 85, 120 ;
amoeboid movement in
collencytes, 52
Amorphinopsis, 153
amphiaster, 134
Amplhiastrella, 152
amphiblastula, 75, 81, 145
Amphibleptula, 149
amphidise, 138

diagnosis

Amphidiscophora, 121

(footnote)
— diagnosis and classifica- |
tion, 122, 123
amphidises, 65, 117 /

diagnosis | Amplilectus, 152

Amphispongia, 123
Amphispongidae, 123
amphitriaene, 134, 146
Aimphius, 150
Amphiute, 110
Amphoriscidae,
and genera, 110
Amphoriseus, 110
Anamixilla, 110
anatriaene, 133
Ancorina, 148
Anisoxya, 150
Anomocladidae, 149
Anomocladinae, 149
Anomoclonella, 149
Anomoclonellidae, 149
Anoplia, diagnosis and
classification, 149, 150
Antares, 148
Anthastra, 148
aphodal type of
system, 35, 130
aphodus, 34, 127
Aphorme, 122
Ap/lvrocallistes, 124
apical formative cell, 107
— ray, 101
Aplysilla, 44, 64, 78, 154
Aplysillidae, 141, 144, 153
— diagnosis and genera,
154
Aplysina, 26, 154
Aplysinidae, diagnosis and
genera, 154
apopyles, 33
aragonite, 167 ,
archaeocytes, 31, 57, 62,
63, 69, 73, 75, 80, 83,
84
Archaeoscyphia, 149
Archaeoscyphidae, 149
arenaceous sponges,

diagnosis

canal

42,

Artemisina, 152

articulated tubar skeleton,
105

Ascaltis, 110

Ascandra, 54, 55, 94, 100,
110

Ascelta, 109, 110

Asconema, 7, 122

Asconematidae, diagnosis
and genera, 122

Ascons, 7, 31, 51, 59, 64,
85, 89, 90, 92, 109, 110,
157, 160

Ascyssa, 109, 110

aster, 117, 134

Asteractinella, 156 ‘

Asteropus, 150

Astraeospongia, 154

Astrobolia, 150

Astrocladia, 149

Astroconia, 123

Astromimus, 151

Astropeplus, 150

Astrophora, diagnosis! and
classification, 147, 148

Astrosclera, 166

Astroscleridae, 168

Astylomanon, 150

Astylospongia, 150

Astylospongidae, 150

Atractosella, 153

attachment, mode of, in
sponges, 2

Aulascus, 122

Aulaxinia, 148

Aulena, 152

Auletta, 153

Aulocalyx, 122

Aulochone, 122

Aulocopidae, diagnosis and
genera, 149

Aulocopium, 149

Aulocystis, 120,.124

Aulosaccus, 122

autodermalia, 118

autophya, 37

170

autoskeleton, 37
axes (geometric) of spicules,
37

axial cross, 116, 118

Axinella, 81, 153

Axinellidae, 138, 140, 145,
151

— diagnosis and genera,
152, 153

Axinellid type of skeleton, |

140

axis (organic) of spicules,
40, 100

Axoniderma, 152

Axosuberites, 151

Azorica, 149

Azoricidae, 148, 150

— diagnosis and genera,
149

Bajulus, 154

Balfour, 158

Barrois, 76 (footnote), 80,
165

basal formative cell, 107

— ray, 101

basalia, 118

Bathydorus, 122

Bathyxiphus, 124

Batzella, 152

Becksia, 124

Bidder, 55, 57, 87, 102, 109

Biemma, 152

bionomics, 88

Blastinia, 111

blastogenesis, 73, 80

blastomeres, 65, 68, 80, 83

blastula, 68, 78

Bolidium, 150

Bolospongia, 149

boring sponges, 88

Bowerbank, 165

PRrachiospongia, 123

Brachiospongidae, 123

Breitfuss, 165

Bubarinae, diagnosis and
genera, 152

Bubaris, 152

budding, 17, 63, 64, 90

Biitschli, 158

Cacochalina, 151
Cacospongia, 153
Calathiscus, 124
Calearea, 1, 3, 24-27, 40,
41, 43, 46, 47, 50, 51,
538, 91, 92-111, 157, 161,
162, 164, 166
calcareous spicules, 40, 100
— origin of, 161
Calcaronea, 109

INDEX TO THE PORIFERA

Calcinea, 109

Callipelta, 149
Callodictyon, 124
Callodictyonidae, 124
Callopegma, 148
Calthropella, 147
calthrops, 132, 135

| Calycosaccus, 122

Calycosoma, 122
Calymmatina, 149
Camerospongia, 124
Caminus, 148

canal system, 85
—- defined, 31

lowe general account of, 31-

— of Calcarea, 92

— of Demospongiae, 125-
130

— of Heterocoela, 96-100

— of Hexactinellida, 111-
116

— of Homocoela, 92-96

candelabrum, 134

Carnosa, 1, 157, 162

— diagnosis and classifica-
tion, 146, 147

Carpospongia, 150

Carter, 49, 56, 85, 86, 89,
158, 164

Carteriospongia, 153

Carterius, 152

Caryomanon, 150

Caryospongia, 150

Casearia, 124

Casterella, 149

Caulocalyx, 122

Caulophacus, 7, 36, 116,
122

cellules sphéruleuses, 49,
59, 144

Celyphia, 111

cement (siliceous) uniting

spicules, 41
central cells, 76
centrotriaene, 134
Cephalites, 125
Ceraochalina, 151
Cerbaris, 152
Cerelasma, 142
Chalina, 151
Chalininae, 156
— diagnosis and genera,

151

Chalinine type of skeleton,
140

Chalinula, 80, 151

chamber layer, 112

chambers, flagellated, 32

Characella, 147

Chaunoplectella, 122

chela, 138

Chenendepora, 150

Chiastoclonella, 149

Chiastoclonellidae, 149

chlorophyll, 25

choanocytes, 27, 53, 62,
121

Choanoflagellata, 27, 53,
62, 89, 159, 160

choanosome, 128

chondrenchyma, 52

Chondrilla, 147

Chondrocladia, 152

Chondropsis, 152

Chondrosia, 145, 147

Chondrosidae, 145, 147

chone, 36,129 °*

Chonelasma, 124

Chonella, 150

Choristida, 135, 157, 163

— diagnosis and classifica-
tion, 147, 148

Chrotella, 147

Cinachyra, 147

Cincliderma, 124

Ciocalypta, 153

circulation, 86

Cladocroce, 152

Cladopeltidae, diagnosis
and genera, 149

cladome, 132

Cladorhiza, 152

cladus, 132

Clathria, 152

Clathrina, 20, 27, 56, 58,
69, 73, 75, 82, 90, 110,
160, 161

— budding, 64

— colours of, 25

Clathrinidae, 7, 48, 53, 93-
95, 100, 103, 104, 107-
110, 119, 145

— diagnosis and genera,
110

Clathriodendron, 152

Clathriopsamma, 152

Claviscopulia, 123

clavula, 117

Clavularia, diagnosis and
classification, 123

Clavulina, 42, 78, 140, 146

— diagnosis and classifica-
tion, 151

Climacospongia, 153

Cliona, 67, 78, 80, 151

Clionidae, 88

— diagnosis and genera,
151

cloacal cavity, 35
— skeleton, 136
clone, 134

‘

.
.

INDEX TO THE PORIFERA

I7I

Cnemidiastrum, 150
Coelocorypha, 150
Coeloptychidae, 124
Coeloptychium, 124
Coeloscyphia, 125
“collar, 27, 54, 55, 121
— cells, 27, 53, 121
collenchyma, 52
collencytes, 52, 62, 120
Collinella, 148
collum, 54
colony, modifications of, in
sponges, 5, 16
Colospongia, 111
colours of sponges, 24
~ Cometella, 151
comitalia, 119
connecting fibres, 141
connective tissue, 51, 81
Conocoelia, 111
consistence of sponges, 26
contractile cells, 44
— vacuoles in collar cells,
54
contractility, 4, 29, 30, 87
conuli, 141
Coppatias, 150
Coppatiidae, diagnosis and
genera, 150
Corallistes, 149
Corallistidae, 148, 150
— diagnosis and genera,
149
Cornacuspongiae, 78, 146,
163
Cornulum, 152
cortex, 32, 97, 105, 129,
136, 162
cortical skeleton, 105
Corticella, 147
Corticidae, 134
— diagnosis and genera,
147
Corticium, 147
Corynella, 111
Coscinoderma, 153
Coscinopora, 124
Coscinoporidae, diagnosis
and genera, 124
Craniella, 67, 147
Crateromorpha, 122
Craticularia, 124
crepis, 134, 162
Crispispongia, 111
Crustacea in sponges, 88
cuticle, 42, 44
cuticular secretion
spongin, 141
— secretions, 41, 43
cuttings, propagation of
sponges by, 64

of

Cyathophycus, 123
Cydonium, 148
Cylindrophyma, 149
Cypellia, 124
Cyrtaulon, 124
cystenchyme, 52
cystencytes, 52, 62
Cystispongia, 124
cytoplasm of collar cells,
54

Dacetylocalyx, 124

Daedalopelta, 149

Damiria, 151

Darwinella, 43, 140, 141,
154, 164

deep sea, influence of life
in, 23

Delage, 49, 82, 158, 159

Demospongiae, 1, 24, 26,
37, 40, 46, 47, 52, 78, 91,
125-154, 156, 157, 161-
164

— canal system, 125-130

— classification, 146-154

— embryology, 78-81

— phylogeny, 161-164

— skeleton, 130-144

Dendoricinae, diagnosis and
genera, 152

Dendoryx, 152

Dendrilia, 141, 154

dendritic sponges, 22

— type of skeleton, 141,
164

Dendroceratina, 1, 78, 145,
146, 153, 163

— diagnosis and classifica-
tion, 154

Dendroclonella, 149

Dendropsis, 153

Dendy, 76 (footnote), 110,
157

Dendya, 94

Dercitus, 147

dermal epithelium, 27, 42,
43, 81

— layer, 27, 84

— membrane, 97, 112, 120,
127

— pores, 127

dermalia, 118

desma, 41, 62, 134

Desmacella, 152

Desmacidon, 152

Desmacidonidae, 152

desmacytes, 52, 62

Desmanthidae, 148

— diagnosis and genera,
149

Desmanthus, 149

14

Deszi, 67

diactinal, 38, 116

— spicules, 137

diaene, 133

Dialytina, 109, 111

— diagnosis and genera,
110

diapedesis, 69

Diaplectia, 111

dichotriaene, 134

Dictyocalyx, 122

Dictyoceratina, 1, 46, 80,
140, 146, 163

— diagnosis and classifica-
tion, 153

dictyonalia, 119

Dictyonella, 153

Dictyonina, 1, 8, 119, 121
(footnote), 156, 157

— diagnosis and classifica-
tion, 123-125

Dictyophyton, 123

Dictyospongidae, 123

digestion, 86

dilophous, 134

diplodal type of
system, 35, 130

Diplodictywin, 124

Dirrhopalum, 152

discoctasters, 120

Discoderinia, 148

discohexactine, 117

discohexaster, 117

Discostroma, 150

distribution, 86

Disyringa, 3, 13, 36, 125,
148

canal

Ditriaenella, 147

diverticula, 7, 32, 90, 98,
96, 104

division of collar cells, 56

Dobie, 56, 158

Dorydesmia, 149

Dorypleres, 150

Dotona, 151

Dragmastra, 148

Dujardin, 89, 158

Ebner, 101
echinating spicules, 140
Echinoclathria, 152
Echinodictyum, 152
Echinonema, 152
Ecionema, 148
ectochone, 129
ectoderm, 81,
159
ectosome, 128
Ectyoninae, 156
— diagnosis and
152

82, 158,

genera,

172

Ectyonine type of skeleton,
140

Ectyonopsis, 152
Eithardia, 9, 110
Elasmocoelia, 111
Elasmostoma, 111
elastic fibrils, 49
embryology, 67
Enantioderma, 159
Enantiozoa, 159
endochone, 129
endogastral networks, 48,
9

endoderm, 62, 73, 81, 158,
159

Eospongia, 150

Epallax, 150

Ephydatia, 152

Epistomella, 150

epithelium, 27

Erylina, diagnosis
genera, 148

Erylus, 148

Esperella, 88, 152

Esperellinae, diagnosis and
genera, 152

Esperia, 152

Esperiopsis, 23, 152

Etheridgia, 124

euaster, 134, 135, 138, 155

Euasterina, diagnosis and
genera, 148

Euastrosa, 147

Eubrochus, 124

Eudea, 111

Eudictyum, 122}

Eumastia, 151)

Euplectella, 6, 37, 41, 64,
116, 120, 122

Euplectellidae, diagnosis
and genera, 121, 122

Euplectellinae, diagnosis
and genera, 122

Euplocalia, 110

Eurete, 124

Euretidae, diagnosis
genera, 124

Euryplegma, 7,23, 115,122

eurypylous type of canal
system, 34, 99, 130

Eusiphonella, 111

Euspongia, 20, 153

Euspongillinae, diagnosis
and genera, 151

Eutaxicladinae, 150

EKuzittelia, 111

Evans, 42, 53, 83, 138

excretion, 87

excurrent canals, 33, 81,99,
113, 126

— duct, 97

and

and

| Geodidae,

exhalant canals, 33
exoderm, 62

Fan-shaped sponges, 22

Farrea, 119, 123

Farreidae, diagnosis and
genera, 123

fertilisation of ovum, 61

fibres of spongin, 42

fibrillae of spongin, 42, 49,
142

Ficulina, 151

Fiedler, 58, 60

Fieldingia, 124

filaments, of HZircinia, etc.,
142 °

Filiferae, 143

first type of canal system,
31, 32

fixation of sponges, 2

flabellate sponges, 22

flagella, 87

flagellated cells, 69, 76, 78,
80, 84

— chambers, 32, 90

flagellum, 27, 54, 85, 121

flat epithelium, 27, 42, 81,
120

flesh spicules, 39, 100, 137

floricome, 117

Fol, 143

Forcepia, 152

formative cells, 107

Fusifer, 152

Ganin, 82

Garstang, 88

gastral actinoblast, 108

— cavity, 3, 35, 71, 81

— layer, 27, 53

— membrane, 112

— ray, 101

— ray, formation of, 108

— skeleton, 105

gastralia, 119

Gastrophanella, 149

Gelliodes, 152

Gelliodinae, diagnosis and
genera, 152

Gellius, 151

gemmule, 65

Geodia, 148

diagnosis and
genera, 148

Geodina, diagnosis” and
genera, 148

Geodites, 148

glandular cells, 138

— epithelium, 27, 42, 46

Gomphostegia, 152

gonocytes, 60, 62

INDEX TO THE PORIFERA

Gotte, 82, 158, 159

Grantessa, 110

Grantia, 9, 47, 110

Grantidae, diagnosis and
genera, 110

Gray, 165

Guettardia, 124

Guitarra, 152

Habrodictyum, 122

Hadromerina, 1, 146, 163

— diagnosis and classifica-
tion, 150, 151

Haeckel, 26 (footnote), 37,
51, 62-64, 89, 96, 101,
109, 142, 143, 158

Halichondria, 56, 88, 151,
157

Halichondrina, 1, 78, 80,
140, 146, 163

—- diagnosis and classifica-
tion, 151-153

Hatlicnemia, 153

Halicometes, 151

Halisarca, 44, 79, 82, 145,
154

Halisarcidae, 146, 153, 164

— diagnosis and genera,
154

Hamacantha, 152

Hamigera, 152

Haplistion, 153

Haploscleridae, 144

— diagnosis and genera,
151

Heider, 158

Hemiasterella, 150

Hertwigia, 122

Hertwigidae, diagnosis and
genera, 122

heteractinal spicules, 155

Heteractinellida, 154, 155,
157, 162

— diagnosis and classifica-
tion, 156

Heterocoela, 1, 8, 75, 109,
164

— canal system, 96-100

— diagnosis and classifica-
tion, 110

— skeleton of, 105

heterogeneous
fibres, 141

Heteromeyenia, 152

Heteropegma, 100, 109, 110

Heterophymia, 149

Heteropia, 110 }

Heteropidae, diagnosis and
genera, 110

Heterorrhaphidae, 151, 152

Heterostinia, 149

spongin

.

>

INDEX TO THE PORIFERA

173

Eee aia

Heteroxya, 150

Hexaceratina, 146, 153, 154

hexactinal, 38, 116

Hexactinella, 124

hexactines, origin of, 162

Hexactinellida, 91, 111-125,
156, 157, 161-164

Hexadella, 145, 154

Hexactinellids, 40

hexaster, 117

Hexasterophora, diagnosis
and classification, 121,
122

Higginsia, 153

Himatella, 111

Hinde, 154, 157, 162, 165

Hindia, 150

Hindiadae, 150

Hircinia, 142, 153

hispid cortical skeleton,
105

— dermal skeleton, 136

hispidating spicules, 136

histocytes, 62, 73, 84

Histoderma, 152

histogenesis, 73, 80

histology, 43-63

— of Olynthus, 27

Holascinae, 119

— diagnosis and genera,
122 |

Holascus, 119, 122

Holasterella, 123 '

Holcospongia, 111 |

holoblastic segmentation,

67, 68

| Holodictyon, 149

Holopsamma, 154

Holoxea, 150
Homaeodictya, 152

_ Homandra, 110
Homasterina, diagnosis and

4 genera, 148

~ Homocoela, 1, 109, 164

— canal system, 92-96

— diagnosis and classifica-
tion, 110

— skeleton of, 103-105

homogeneous spongin libres,
140

Homorrhaphidae, 151

Hoplophora, diagnosis and
classification, 148, 149

Hundeshagen, 42

Hyalascus, 122

Hyalonema, 41, 123

Hyalonematidae, 113, 115,
117, 119, 121 (footnote)

— diagnosis and genera,
123

Hyalonematinae, 123

e— -

Hyalospongiae, 1
Hyalostelia, 123
Hyalostylus, 122
Hyalotragos, 150
Hydrozoa in sponges, 88
Hymedesmia, 151
Hymeniacidon, 153
Hymeraphia, 152
Hymerhabdia, 152
hypodermalia, 119
hypophare, 126

Tanthella, 141, 154

immigration, 69, 75

impersonal condition, 21,
91, 125

incrusting sponges, 22

incurrent canals, 32, 97,
127

individuality, 89

— loss of, 20, 91, 125

Inermia, diagnosis
classification, 124, 125

inhalant canals, 32

Inobolia, 111

intercanal system, 93, 96

intracellular spongin, 50

Tophon, 152

Totrochota, 152

irregular type of skeleton, |

135
Ischadites, 123
Tsops, 148
Isoraphinia, 149

James-Clark, 54, 62, 89,
158

Jerea, 149

Jereica, 150

Jorunna, 88

Joyeuxia, 152

Kaliapsis, 148

Kalpinella, 149

Kalykenteron, 152

Kazania, 150

Keller, 43, 120, 137, 165

Keratosa, 1, 3, 24, 26, 78,
80, 139, 145, 146, 156,
157, 163

— diagnosis and classifica-
tion, 153, 154

— skeleton of, 140-144

Kirkpatrick, 168

Kérnerzellen, 76 (footnote)

Krukenberg, 26, 42

Lamontia, 110
Lankester, 59
Lanuginella, 122

and

Lanuginellinae,
and genera, 122

larva, 69, 73, 78, 89, 160

larvae of Demospongiae,
144

Lasiocladia, 153

lateral ray, 101, 105

Latrunculia, 151

Laxosuberites, 151

Lecanella, 149

Lefroyella, 124

Leiodermatium, 149

Leiodorella, 150

Lelapia, 106, 110

Lendenfeld, 44 (footnote),
46, 47, 57 (footnote), 116,
141, 142, 156, 163, 165

Leptophragma, 124

Leptosia, 152

Lessepsia, 152

Eeucandra, 19, 48, 99, 110

Leucascus, 110

Leucilla, 99, 110, 113

Leuckart, 62, 158

leuconoid type of canal
system, 98-100, 167

Leucons, 90, 92, 96, 109,
113

Leucopsacinae,
and genera, 122

Leucopsacus, 122

Leucosolenia, 17, 51, 56,
110

Leucosoleniidae, 7, 48, 64,
75, 93, 94, 100, 101, 104,
105,107,145 ~

— diagnosis and genera,
110

Leucyssa, 110

Licmosinion, 125

Lieberkiihn, 85,
158, 164

lipogastry, 4

lipostomy, 4

Lissodendoryx, 152

Lister, 166, 168

Lithistida, 41, 134, 135,
157, 162

— diagnosis and classifica-
tion, 148-150

Lithonina, 109

Lithoninae, diagnosis and
genera, 111

Loisel, 49, 59, 86, 87, 89,
143, 144

lophocalthrops, 134

Lophocalyz, 64, 122

lophotriaene, 134

Lubomirskia, 151

Luffaria, 154

Lyidium, 149

diagnosis

diagnosis

86, 89,

174

Lymnorea, 111

Miklucho-Maclay, 64

INDEX TO THE PORIFERA

Olynthus, anatomy and his-

Lyssacina, 1,3, 116,119,156
— diagnosis and classitica-
tion, 121-123

Maas, 49, 57, 80-82, 96,
107, 144

Macandrewia, 149

macromeres, 80

Maeandrospongidae, diag-
nosis and genera, 124

Magog, 150

Malacosaccus, 122

maltha, 51

Mantell, 7

mantle of spongoblasts, 46,
141

Margaritella, 124

marginalia, 118

Marshall, 142

Marshallia, 124

massive sponges, 22

Masterman, 57

Mastosia, 149

maturation of ovum, 61

Megalithista, 149

Megamorina, 149

megascleres, 100, 130, 137

— definition of, 39

Meliiderma, 152

Mellittionidae,
and genera, 124

Mellonympha, 122

Melonanchora, 152

Melonella, 149

membrana reticularis, 121

Menanetia, 151

Merejkowsky 44 (footnote)

mesoderm, 63, 73, 81, 85

mesogloea, 51, 86

mesotriaenes, 146

metamorphosis, 69, 81, 84

Metschnikoff, 73, 80, 82,
85, 86, 165

Metschnikowia, 151

Meyenia, 152

Meyeninae, diagnosis and
genera, 151, 152

microcalthrops, 134

Microciona, 152

micromeres, 80

microrhabdus, 134, 135

microscleres, 100, 130, 137, |
138

— definition of, 39

Microsclerophora, diagnosis
and classification, 147

Microtriaenosa, diagnosis
and classification, 146,
147

Microtylotella, 152

diagnosis |

Minchin, 57
monactinal
116, 137
monaene, 133
Monakidae, 123
Monanchora, 152
monaxon spicules, 38, 116,
133, 137, 163
Monaxonida, 1, 3, 23, 24,
26, 80, 145, 146, 156,
157, 163
— diagnosis and classifica-
tion, 150-153
— skeleton of, 137-140
Monoceratina, 153
monocrepid, 135
Monocrepidium, 149
monolophons, 134
morphogenesis, 73, 81
multipolar immigration, 75
Myliusia, 124
myocytes, 44, 62, 144
Myriastra, 148
Myrmecium, 111
Myzxilla, 152
Myxospongida, 1, 26, 52,
145, 146, 164
— diagnosis and classifica-
tion, 154

spicules, 38,

Nematrinion, 149
Neopeltidae, diagnosis and
genera, 149

Neopeltis, 149
Veosiphonia, 148
nephrocytes, 57
nervous system in sponges,
46, 87
networks in gastral cavity,
48, 96
Nipterelia, 150
Noldeke, 83, 158, 159
non - articulated tubar
skeleton, 105
Nudibranchs, feeding on
sponges, 88
nutrition, 85

Oceanapia, 152
octactinal spicules, 155
Octactinellida, 154, 155,
157, 162
— diagnosis and classifica-
tion, 156
Oculispongia, 111
odour of sponges, 26
Oligosilicina, diagnosis and
classification, 147
Olynthus, 3, 7, 8, 64, 90,
92, 103, 104, 126, 161

2 EEE

tology, 26
Onchocladinae, 149
Oncosella, 123
odgenesis, 61
Ophirhaphidites, 148
Ophlitaspongia,.152
Ophrystoma, 124
organic axis of spicules, 40,

100

organogeny, 81

orthotriaene, 133

Oscarella, 44, 49, 64, 127,
145, 147, 154, 160, 164

Oscarellidae, 146, 164

— diagnosis and genera,
154

oscular rim, 27, 93

— tubes, 93

osculum, 3, 27, 35, 72, 85,
87

ostia, 33, 36, 48, 85, 97,
127, 129

overgrowth, 71

oxeote spicules, 101, 137

oxyaster, 134

oxyhexactine, 117

oxyhexaster, 117

Pachastrella, 147
Pachastrellidae,
and genera, 147
Pachinion, 150
Pachychalina, 151
Pachymatisma, 148
Pachypoterion, 149
Pachyteichisma, 125
Pachytilodia, 111
Palaeomanon, 150
Palaeosaccus, 123
palpocils, 47
Papyrula, 148
Parazoa, 159
parenchyma, 31, 51, 88,
120

diagnosis

parenchymal skeleton, 106,
119

parenchymalia, 119, 167
parenchymula, 69, 75, 80,
145
parietal gaps, 37, 116
Parmula, 152
parthenogenesis, 67
Pattersonia, 123
Pattersonidae, 123
pedunele, 3
peduncular skeleton, 105
pedunculate sponges, 4
Pekelharing, 55, 57, 85, 87
pelagic larvae, 73
Pellina, 151

—

INDEX TO THE PORIFERA

_Pemimatites, 150
Penares, 148
pentactinal, 38, 116
Pericharax, 110
Periphragella, 124
peristomial skeleton, 105
Peronella, 111
Peronidella, 111

person, modifications of, in|

sponges, 5
Perty, 89
Petromica, 149
Petrosia, 151
Petrostroma, 100, 106, 109,
111
phagocytes, 58, 62, 85
phagocytosis, 82, 83
Phakellia, 23, 153
Pharetronidae, 106, 109,
157, 168
— diagnosis and genera, 110
Pharetrospongia, 111
Phelloderma, 152
Pheronema, 123
Phioeodictinae,
and genera, 152
Phlyctenium, 125
Pholidocladia, 149
Phoriospongia, 152
Phormosella, 123
Phyllospongia, 153
Phymaplectia, 149
Phymatella, 148
Physcaphora, 148
physiology, 85
Pilochrota, 148
pinacocytes, 44, 62
pinulus, 117
Placonella, 149
Placoplegma, 122
Placortis, 147
Placospongia, 148
Placospongidae, 133, 145
— diagnosis and genera, 148
Placotrema, 124
Plakina, 78, 82, 126-129,
145, 147, 162
Plakinastrella, 147
Plakinidae, 162
— diagnosis and genera, 147
Plakinolopha, 147
planula, 82
plasmodium, 41
Platychonia, 150
Plectispa, 152
Plectoderma, 123
Plectospongiadae, 123
Pleroma, 149
Pleromidae, diagnosis and
genera, 149
pleuralia, 118

diagnosis

Plewrope, 124
Pleurostoma, 124
Plinthosella, 149
Plocamia, 152
Plocoscyphia, 124
plumicome, 117
Plumohalichondria, 152
plumose fibres, 140
Pocillon, 152
Poecillastra, 147
Poecilocladinidae, 149
Poeciloscleridae, 138, 145

— diagnosis and genera, 152 |
Polejaetf, 60, 100, 105, 109,

142
Polejna, 110
Poliopogon, 7, 119, 123
Pollakidae, 123
polyaxon, spicules, 39, 132,
134

Polyblastidium, 125
Polyjerea, 149
Polylophus, 122
Polymastia, 151
Polymastiidae, diagnosis
and genera, 151
Polysteganinae, 111
pores, 3, 27, 35, 85
— formation of, 72
Poritella, 149
Porochonia, 124
Porocypellia, 124
porocytes, 27, 28, 48, 62,
71, 85, 108, 144
Porospongia, 124
Porosponginae, 124
posterior granular cells, 69,
71, 73
— ray, 101, 105
Potamolepis, 152
Poterion, 151
Porziella, 152
primary cell differentiation,
73
— spicules, 40, 131
principal fibres, 141
principalia, 119
Prophysema, 154
prosodus, 35, 49, 127
prosopyles, 33, 48, 126, 127
prostalia, 118
Prosuberites, 151
Protachilleum, 150
Proteleia, 138, 151
Proterospongia, 160
Protolynthus, 31, 161
Protospongia, 123, 157
Protospongidae, 123
Protosycon, 111
protriaene, 133
Psammastra, 148

| Psammina, 154
Psamminidae, 142
— diagnosis and genera,
154
Psammoclema, 154
Psammopemma, 142, 154
pseudoderm, 95, 97, 104
| pseudogaster, 23, 95, 116
pseudopodia, 71
— incollencytes, 52
pseudopore, 95, 97
pseudosculum, 23, 95
pseudoskeleton, 37
Pseudosuberites, 151
Purisiphonia, 124
Pycnopegma, 149
pylocyte, 48
Pyrgochonia, 150
Pyritonema, 123
Pytheas, 152

quadriradiate spicules, 101
— formation of, 107, 108
Quasilina, 151

Rachella, 147

Racodiscula, 148

radial tubes, 96

radiate type. of skeleton,
135, 140

Radiolaria, 43

Ragadinia, 149

Raphidonema, 111

Raphidophlus, 152

Raphisia, 151

Raspailia, 153

Rauff, 109, 134, 165

Rauffia, 111

Receptaculites, 123

Receptaculitidae, 123

Regadrella, 6, 122

regular triradiates, 101

Reniera, 59, 67, 144, 151

Renierinae, diagnosis and
genera, 151

Renierine type of skeleton,

Reniochalina, 151

reticulate type of skeleton,
140, 141

Rhabdasterina, diagnosis
and genera, 148

Rhabderemia, 152

rhabdi, 137

Rhabdocalyptus, 122

Rhabdodictyum, 122

rhabdome, 132, 163

Rhabdoplectelia, 122

Rhabdosa, 149

rhabdus, 116, 133

176

INDEX TO THE PORIFERA

Rhagon, 64, 125, 135, 164

Rhaphidistia, 150

Rhaphidorus, 151

Rhasxella, 148

Rhizaxinella, 151

Rhizchalina, 152

Rhizomorina, 148-150

Rhizopoterion, 125

Rhopalospongia, 149

Ridleia, 151

Ridley, 157

Rimella, 148

Roemer, 155

root tuft, 3, 41, 88, 118

rosette, 117

— cells, 80

Rossella, 122

Rossellidae, diagnosis and
genera, 122

Rossellinae, diagnosis and
genera, 122

Rostanga, 88

Saccocalyx, 122 5
sagittal triradiates, 101
Samus, 147
sanidaster, 134
Sanidasterina,
and genera, 148
Sanidastrella, 148
sarcenchyma, 52
Savile-Kent, 55, 89, 158
Sceptrintus, 151
Schaudinnia, 121, 122
Schizorhabdus, 125
Schmidt, 143, 165
Schulze, 42, 44 (footnote),
52, 62, 64, 76 (footnote),
111, 120, 121, 127, 135,
143, 156, 159, 162, 165
Scleritoderma, 149
Scleritodermidae, diagnosis
and genera, 149
scleroblasts, 27, 39, 47, 53,
62, 107, 120
Sclerochalina, 151
Sclerokalia, 124
Scleroplegma, 124
Sclerothamnus, 124
Scolopes, 150
scopula, 117, 118
Scopularia, diagnosis and
classification, 123, 124
Scyphidium, 122
Scytalia, 149
second type
system, 32
secondary cell differentia-
tion, 73
— spicules, 40, 131, 134
— symmetry, 23

diagnosis

of canal

segmentation of ovum, 67,
68, 73

Seiriola, 148

Seliscothon, 150

Semisuberites, 151

Semperella, 123

Semperellinae, 123

sensitiveness, 87

sessile sponges, 4

Sestrocladia, 125

Sestrodictyon, 124

Sestrostomella, 106, 111

Setidium, 149

sheath of spicule, 40, 100

Sideroderma, 152

sieve membrane of osculum,
27

sigma, 138

sigmaspire, 134

Sigmatella, 152

Sigmatophora, diagnosis
and classification, 147

Sigmaxinella, 153

Silicea, 162

siliceous spicules, 40

— spicules, origin of, 161

Siphonia, 13, 148

Siphonidium, 149

Siphonochalina, 151

skeletal spicules, 39, 100,
137

skeletogenous cells, 85

— layer, 46

— stratum, 31, 51, 62, 71

skeleton, 27

— in general, 37-43

— of Calearea, 100-107

— of Demospongiae, 130-
144

— of Hexactinellids, 118-
120

— of Keratosa, 140-144

— of Monaxonida, 137-140

— of Tetraxonida, 130-137

— origin of, 161

smooth cortical skeleton,
105

Sollas, 44, 47, 52, 58, 135,
148, 158, 159

Sollasella, 153

Sollas’s membrane, 56

Spanioplon, 152

spermatocyst, 60

spermatocyte, 60

spermatogenesis, 60

spermatogonium, 60

sphaeraster, 134

Sphaerospongia, 123

Sphaerotylus, 151

Sphenaulax, 124

Sphenophorina, 110

spherule, 167

sphincter, 27, 36, 46, 48

Sphinctrella, 147

spicular system, 40

spicule, definition of, 41

spicules, 27, 71

— calcareous, 40, 100

— development of, 40

— formation of, in Calcarea,
107, 108

— morphology of, 37

— of Darwinella, 141

—of Hexactinellids, 116-
118

— of Monaxonida, 187,
138

— of Octactinellida and
Heteractinellida, 155

— of Tetraxonida, 131-135

— organic axis of, 40, 100,
116, 118, 167

— origin of, 161

— sheath, 40, 100

— siliceous, 40

Spiculispongiae, 146, 163

Spinosella, 151

Spiractinella, 123

Spirastrella, 43, 151

Spirastrellidae, diagnosis
and genera, 151

Spiroxya, 150

Spongelia, 154

Spongeliidae, 142, 144

— diagnosis and _ genera,
153, 154

Spongicola, 88

Spongidae, diagnosis and
genera, 153

Spongilla, 42, 51, 53, 56,
58, 61, 80, 82, 86, 89,
151, 159

Spongillinae, 1, 25, 65, 67,
137, 138

— diagnosis and genera,
151, 152

spongin, 138, 163

—- chemical nature, 41

— fibres, 26

spongoblasts, 42, 46, 62
138, 141 ©

spongoclasts, 141

Spongodiscus, 149

spongophare, 126

Spongosorites, 150

spongozoon, 89

Sporadopyle, 124

Sporadoscinia, 125

sporaster, 134

Stachyspongia, 150

stalk, 3

Stannarium, 154

mt al cme

:

i

Stannoma, 154

Stannomidae, 142, 143

— diagnosis and genera,
154

Stannophyllum, 154

statocytes, 60, 62, 65

Stauractinella, 123

Staurocalyptus, 122

Stauroderma, 124

Staurodermidae, 124

Stauroderminae, 124

Stauronema, 124

Stelletta, 43, 128, 148

Stellettidae, diagnosis and
genera, 148

Stelligera, 153

Stellispongia, 111 /

Stelospongus, 142, 153

Stephanoscyphus, 88

sterraster, 134

Sterrastrosa, 148 |

Stewart, 47 |

Stichophyma, 150

stomions, 127

Strambergia, 111

streptaster, 134, 138

Streptasteridae, diagnosis
and genera, 150

Streptastrosa, 147 |

strongylote, 137

Stryphnus, 148

Stuckenbergia, 149

style, 133

Stylocordyla, 151 |

Stylocordylidae, diagnosis |
and genera, 150, 151

Stylostichon, 152

Stylotella, 152

Stylotrichophora, 152

stylus, 116, 137

subcortical crypt, 129

subdermal cavities, 128

— trabecular layer, 112

Suberites, 88, 151, 157

Suberitidae, 140

— diagnosis and genera,
151

Suberotelites, 152

subgastral trabecular layer, |
112

Sulcastrella, 148

Sycantha, 110

Sycetta, 110

Sycettidae, 111

— diagnosis and genera,
Oe &

Sycon, 8, 27, 48, 55, 56,
61, 76, 77y 81, 82, 100,
105, 107, 110

syconoid type of canal |
system, 96, 97

INDEX TO THE PORIFERA

Sycons, 90, 92, 96, 109
Syculmis, 110

Sycyssa, 110
symmetry, secondary, 23
Sympagella, 122
Sympyla, 149
synapticula, 119
syncytium theory, 62
synocils, 47

Synopella, 111

Synops, 148
Syringella, 153

Taegeria, 122

Taegerinae, diagnosis and
genera, 122

Tedania, 152, 156

| Teganium, 123

Teichonella, 110

| Tentorium, 13, 20, 36, 151,
167

Terpios, 151

tego! cell differentiation,

| Tethya, 64, 67, 150

Tethyidae, 133, 138

— diagnosis and genera,
150

Tethyopsilla, 147

Tethyopsis, 148

| Tethyorrhaphis, 150

Tetilla, 127, 128, 147

| Tetillidae, diagnosis and
genera, 147
Tetracladidae, diagnosis

and genera, 148
tetracrepid, 135

| tetractinal, 38, 116

tetractine, 132

Tetractinellida, 1, 3, 78,
132, 146, 157

— diagnosis and classifica-
tion, 147-150

tetralophous, 134

| Tetranthella, 153

‘tetraxon spicules, 38, 132

— spicules, origin of, ines
162

Tetraxonia, 162, 164

| Tetraxonida, 1, 145, 146, |

163
— diagnosis and classifica-
tion, 146-150
— skeleton, 130-137
Thalamopora, 111
Thamnospongia, 149
Thecaphora, 151
Thecosiphonia, 149
Thenea, 147, 157
Theneidae, diagnosis and
genera, 147

177

Theonella, 148
thesocytes, 58, 59, 62
third type canal system,
33
| Tholiasterella, 156
| Thoosa, 151
| Thorecta, 154
| Thrinacophora, 153
| Thrombus, 147
| Thymosia, 147
| tokocytes, 58, 59, 62, 83
| Topsent, 49, 59, 65, 67
| 127, 144, 165
| tornote, 137
Toulminia, 124
' toxa, 138
Toxochalina, 151
trabeculae, 112, 120
| Trachya, 150
| Trachycaulus, 122
Trachycladus, 150
| Trachysimia, 111
Trachysycon, 148
| Trachytedania, 152
Tragosia, 153
Tremadictyon, 124
Tremaulidium, 149
Tretodictyidae, diagnosis
and genera, 124
Tretolophus, 149
triactinal, 38
; — Spicules, 101
triaene, 132, 135
triaenes, 162, 163
Triaenosa, 148
| triaxon spicules, 38
| — origin of, 162
Triaxonia, 111, 162, 164
Tribrachion, 13, 148
Trichasterina, 122
Trichospongia, 153
Trichostemma, 151
| Trikentrion, 138, 153
_ trilophous, 134
| tripods, 104
| Triptolemus, 147
/ triradiate spicules, 101
— spicules, formation of,
107
| Prochobolus, 125
| Trochospongilla, 151
| trophocytes, 58, 62
| Tuba, 151
_tubar skeleton, 105
| — system, 93
beers 152
Tuberella, 150
‘tuning. fork spicules, 106
| Turonia, 149
| tylhexactine, 117
| Tylosigma, 152

.

178 INDEX TO THE PORIFERA

tylostyle, 137
tylote, 137
Typton, 88

Uncinataria, diagnosis and
classification, 123, 124

uncinate, 117

undergrowth, 71

unipolar immigration, 75

Uruguaya, 152

Ute, 9, 110

Utella, 110

Vasseur, 64

vegetative reproduction, 63 Vosmaeropsis, 110

Walteria, 122
wandering cells, 28, 31
Weltner, 165

Willey, 166

Wright, 157

| Velinea, 154

| Ventriculites, 3, 7, 125

| Ventriculitidae, 125
Verongia, 154
Verrucocoelia, 124
Verruculina, 150
Verticillites, 111
Vetulina, 149
Vibulinus, 153
Vitrollula, 122 yolk granules, 65, 83
Vomerula, 152 | Yvesia, 152
Vosmaer, 55, 57, 85, 87, |

163, 165 | Zittel, 165, 168

Vosmaeria, 110, 153 zoa impersonalia, 91

zygosis, 137

xenophya, 37
Xenospongia, 151

—

CHAPTER IV

THE HYDROMEDUSAE.!

CLASS HYDROMEDUSAE.

Order 1. Anthomedusae.
» 2. Leptomedusae.
3. Trachomedusae.
4. Narcomedusae.
5. Hydrocorallinae.
,, 6. Siphonophora.
Sub-Order 1. Disconectae.
45 2. Calyconectae.
. Physonectae.
. Auronectae.
. Cystonectae.

OL Hm Oo b

THE organisms which are dealt with in this chapter and the next
under the class-names Hydromedusae and Scyphomedusae were,
until quite lately, regarded as being so much more closely allied to
each other than to any other class of the animal kingdom that they
were grouped together under the name Hydrozoa (a name due
originally to Huxley), in contrast to the other great division of
Coelentera, the Anthozoa. It has, however, become increasingly
probable that, near akin as are Scyphomedusae to Hydromedusae,
their race-history indicates a yet closer relationship to Anthozoa ;
the term Hydrozoa has therefore been dropped altogether for the
purposes of the present work, although the further step of uniting
Scyphomedusae and Anthozoa under the class-name Scyphozoa (as
some suggest) has not been taken.

DEFINITION.—Hydromedusae are Coelentera, which typically
present two main forms of individuals—the non-sexual hydroid and
the sexual medusoid (gonophore) ; in this case the life-history
exhibits an alternation of generations, in which the hydroid pro-
duces the medusoid by lateral budding, and the fertilised eggs of the

1 By G. Herbert Fowler, B.A., Ph.D.

THE HYDROMEDUSAE

tN

medusoid develop into a hydroid. In other cases the medusoid
may develop directly from an egg-cell, or may be budded from
another medusoid. No gastric ridges or filaments occur in
either hydroid or medusoid. The sexual cells lie typically on
radii of the first order, and are always (?) primarily derived from
ectoderm cells. The medusoids are characterised by the possession
of a muscular non-vascular velum, and have as sense organs ocelli,
otocysts, or tentaculocysts.

Tue DIBLASTULA AND THE EmMpryonic LAyers.—The single
form of Hydromedusan cell, which was excepted above as being
capable of independent existence, is called the egg or ovum. If duly
fertilised the ovum shortly splits into two cells, which in their
turn divide again; this process of division, or segmentation of the
ovum, is continued until ultimately, by one path or another, an
embryo has been built up which consists of numerous cells, arranged
in two layers round a central cavity. To an embryo of this kind
the name diblastula (gastrula) has been given (Fig. 2). These
two layers of cells, however complex may be the ultimate form
of the adult organism, are the chief constituent tissues of all
Hydromedusae, as was shown by Huxley so long ago as 1849.
To the outer layer or skin has
been assigned the name ecfo-
derm ; the inner layer which
lines the central cavity or
coelenteron has been termed the
endoderm. Between the ecto-
derm and the endoderm is
deposited later a gelatinous
secretion, the non-cellular meso-
gloea, into which cells from either

Fic. 1. Fic. 2. of the two primary layers may
1.—Section through a blastula; the singlelayer wander, From these simple

of cells surrounds a cavity, the blastocoele. At

the lower pole two cells of the future endoderm elements — ectoderm meso-
have been budded into the blastocoele. i oe
2,—Section through a diblastula (gastrula). gloea, and endoderm lining the

The cells of the future ectoderm are ciliated; | : >
by their proliferation a number of cells, the future coelenteron—all the vat ied and
endoderm, have been budded into the blastocoele, Jseqautiful forms of the Hydro-

which they nearly fill.
medusae are moulded.

GENERAL DESCRIPTION OF THE HYDROID AND OF THE MEDUSOID.
—In no group of the animal kingdom is polymorphism carried to a
greater extent than in the Hydromedusae, yet, upon morphologival
analysis, the numerous forms which individuals exhibit are
apparently all referable to modifications of one or other of two
main types—the Hydroid and the Medusoid.

The Hyprom (hydriform person, hydranth, trophozooid) is
represented in a simple form by the genus Hydra, from which it
derives its name. This presents (Figs. 3, 4, Band C) a tubular

a

body consisting of ectoderm, mesogloea, and endoderm, at one
end of which is a mouth, situated on a slight eminence (the
hypostome); through the mouth the internal cavity (coelenteron)
communicates with the outer world. Round the mouth are placed
tentacles, which are hollow outgrowths of the body, their cavity
being part of the coelenteron.

In the hydroid thus composed the elements of the original
diblastula are not far to seek: the primary two layers, ectoderm

THE HYDROMEDUSAE 3

Fic. 3. Fic. 4.

3.—Hydra viridis, attached to a piece of weed. ov, ovary ; te, testis.

4.—Diagram exhibiting the plan of structure of hydroids. A, hydroid with wide
disc, manubrium, and solid tentacles (Tubularian); B, hydroid with narrow disc and
hollow tentacles (Hydra); C, transverse section of the body of a hydroid. All the figures
show from without inwards ectoderm (strongly hatched), mesogloea (a thick black line), and
endoderm (lightly hatched), surrounding the coelenteron.
and endoderm, and the coelenteron, are still represented. The
secretion of a mesogloea, the perforation of a mouth, and the out-
growth of tentacles, are the main morphological differences between
embryo and adult hydroid.

Hydroids are either solitary or colonial. The solitary forms,
such as Hydra, are capable of reproduction by a process of budding
(Braem, 15; Seeliger, 16), (Fig. 4, 6), in which a part of the body
wall, enclosing coelenteric cavity, protrudes laterally ; this elon-

' gates and forms a mouth and tentacles at its distal end; the little
Hydra, thus produced, becomes constricted off by aningrowth of cells,

which seal up both its central end and the body wall of the parent.

4 THE HYDROMEDUSAE

A process of budding, similar in character but not followed by
a separation of progeny from parent, results in the production of

colonial forms (Figs. 16 to 20); in the colony thus formed, the

SesetG
? OX? Pres ws webseeacasnastvaeEe
eeetrmnittnn tn

EU
Fic. 5.

QD
te,

O Q Tu
tty wi mnie Wins
7"

Fira. 6.

5.—Section of a medusoid, placed mouth upwards for comparison with a hydroid (Fig. 4).
The right half of the section is taken along a radial canal, the left half between two radial
canals. CC, circular canal; EU, exumbral surface; G, gonad or generative cells lying in the
ectoderm of a process of the subumbral body wall (characteristic of Leptomedusae); GC’,
gonad lying in the ectoderm of the manubrium (characteristic of Anthomedusae); GL, gastral
lamella; M, manubrium ; NR, the outer, and NR’, the inner parts of the nerve ring ; RC, radial
canal; SU, subumbral cavity; 7, tentacle; V, velum. Body layers represented as in
Fig. 4.

6.—Section of a medusoid, at right angles to Fig. 5. Letters as in Fig. 5; body layers as in
Fig. 4.
7.—Diagram showing the chief radii of a medusoid. P, perradii (the first four radii
accentuated in development); J, interradii ; A, adradii,

coelenteron of each hydroid communicates with those of all the
other hydroids through the tubular coenosare or common tissues.

THE HYDROMEDUSAE 5

The coenosare generally consists of a branching vertical stem (the
hydrocaulus), springing from a branching horizontal stolon (the hydro-
rhiza), by which attachment is effected to some foreign body. A trans-
verse section of either hydrocaulus or hydrorhiza typically presents
the same ectoderm, mesogloea, and endoderm lining coelenteron, as
are exhibited by a section of a Hydra or of its tentacle (Fig. 4, C).
Theoretically, in the Anthomedusae an axial stem or branch is only
the much elongated body of the terminal hydroid of that stem or
branch ; but as in practice it is often difficult to allot the parts
correctly, the tubular stems and branches are treated as coenosarc
or tissues common to the colony.

The coenosare is generally invested by a horny coat, the perisare,
formed as a secretion by the ectoderm cells; this in some cases
expands into a hydrotheca (Fig. 17) at the base of each hydroid, in
others (Fig. 16) it ceases abruptly at that point.

Hydroids are formed either as buds from other hydroids, or as
buds from the coenosare, or directly from a fertilised ovum; they
are generally fixed, sterile, and nutritive.

The MeEpusorD (medusiform person, gonozooid, gonophore)
exhibits all the parts of a hydroid, but in slightly altered relations.
It is generally bell-shaped (Figs. 5, 25, 33), the clapper of the bell
being formed by a projection (the manubrium), at the end of which is
the mouth. The bell itself is often termed the wmbrella ; its oral or
concave face is styled the subumbral, and its aboral or convex face
the exumbral surface. From the lip of the bell or umbrella a shelf
(the velwm) projects inwards, and the tentacles hang downwards.
The mouth opens through the manubrium into an expanded gastric
cavity ; from this four perradial canals lead to the lip of the bell and
there open into a circular canal which runs round its circumference.

Although the relation of this organism to the hydroid is not
obvious at first sight, a comparison of Figs. 4 and 5 will make
it clear. The elongated hypostome of the hydroid corresponds to
the manubrium of the medusoid ; the tubular body of the hydroid,
if expanded radially outwards in every direction, would represent
the bell-shaped body of the medusoid ; the tentacles would be
carried outwards by this expansion, but would remain as a circlet
round the hypostome (manubrium).

While the outward form of the medusoid is thus referable to
that of the hydroid, the coelenteron of the former is not of the
simple nature which is presented by that of Hydra; the endo-
derm is no longer uniformly the lining of the coelenteron, but
forms a solid cup-shaped plate (the gastral or endoderm lamella), lying
in the wall of the umbrella between the gastric cavity and the circular
canal, except along certain lines which have been already cited as
the radial canals (Figs. 5, 6). The coelenteron thus consists
of the following regions, manubrial cavity, gastric cavity, radial

6 THE HYDROMEDUSAE

canals, circular canal, and sometimes tentacular canals; the
endoderm, in addition to forming the lining of these cavities,
forms the endoderm lamella, and sometimes a solid tentacular core.

The perradial canals lie
in the first four radii (Fig. 7)
which are accentuated in the
development of the medu-
soid; other four radiating
canals may be similarly
formed between these, which
: with them divide the um-
» aria Bar of section of durin showing brella into eight equal parts ;
gastral lamella ; en, endoderm lining gastric cavity. they are termed interradial.
(From Lankester, after Hertwig). A further set of eight radi-
ating canals is sometimes developed between perradial and inter-
radial canals, and is termed adradial.

The exumbral mesogloea is generally greatly thickened and
adds firmness to the bell.

When medusoids are attached to a hydroid colony, the perisare
in some cases expands into a gonotheca for their protection (Fig. 17) ;
in other cases it is absent (Fig. 16).

Medusoids are formed either as buds from hydroids or from
hydroid coenosare, or as buds from other medusoids, or directly
from the fertilised ovum. They are typically free swimming and
fertile, and are often incapable of taking food.

HistToLoGy OF THE Hyproip (Figs. 8 to 10) (Jickeli, 17;
y. Lendenfeld, 18).— The ectoderm is generally composed of a
single layer of cells, and includes several varieties of cell forms.
Of these the most prominent are the large epithelio-muscular cells,
the inner ends of which give off contractile fibres in a direction
parallel to the long axis of the body; these fibres, which fre-
quently exhibit striations, are attached to the mesogloea, and
the movements of the body are largely effected by their means.
In some cases a gradual diminution can be traced in the size of
the cell body, and a corresponding increase in the size of the
muscular fibre; this leads to a deep-lying muscle cell, no longer
epithelial, comparable to the smooth muscle cell of Triploblastica
(Fig. 8, 1-8). The possession of a stiff sensory filament, the palpocil,
characterises the sense cells. Other cells, provided with a similar
filament, the cnidocil, are termed cnidoblasts, and secrete in the
interior of the cell body the nematocyst, a weapon of offence and
defence. This consists (Figs. 8°, 9) of a vesicle, often with double
walls, filled with fluid, the neck of which is barbed and then drawn
out into a long and extremely fine tubular filament, at the tip of
which the tube probably opens to the exterior. When in the cell,
the nematocyst has a different appearance ; the filament, barbs, and

|

7]

—

THE HYDROMEDUSAE 7

neck, are formed and lie inside the vesicle, and are everted only by
pressure upon its walls. Two kinds of nematocyst, a larger and a
smaller, are generally present, and exhibit some differences of
detail. Gland cells and pigment cells are not uncommon. Multi-
polar ganglion cells, lying beneath the surface of the ectodermal
_ epithelium, have been detected in numerous species. The smaller
interstitial cells, of irregular form, which fill the interspaces between

Fic. 9. Fic. 10.

8.—Types of Hydromedusan cells, after von Lendenfeld and Schulze. 1, epithelio-muscular

cell, with palpocil and contractile processes ; 2, 3, muscular cells showing the transition from
the ‘epithelioid to the fibrous condition; 4, sense cell with palpocil, connected by nerve fibre
with ganglion cell; 5, supporting cell with palpocil ; 6, enidoblast, with three enidocils, en-
closing a Tematocy st, and connected by nerve fibre with "ganglion cell ; . 7, endoderm cell with
cilium ; the protoplasm is vacuolated and contains (7) food particles; 8, amoeboid cell from
mesogloea.

9.—Cnidoblast with cnidocil and nematocyst; the thread and barbs of the latter have
been everted. (After Schulze.)

10.—Vacuolated endoderm cells of ‘‘ cartilaginous” consistence from the axis of the tentacle
of Cunina. (From Gegenbaur's Elements of Comparative Anatomy.)

the others, are apparently differentiated as required into the more
specialised cell forms already mentioned.

The endoderm is also generally composed of a single layer of
cells, and is ciliated; there is generally one cilium on each cell,
which is capable of withdrawal. The larger cells of the endodermal
epithelium are essentially digestive cells, but are in many cases also
provided with short contractile fibres which lie on the mesogloea

8 THE HYDROMEDUSAE

in a direction at right angles to the long axis of the body and to
the contractile fibres of the ectoderm. The cells are often
amoeboid at the outer or free end, and contain vacuoles filled with
an albuminous fluid. Particles of food-matter and masses of (?)
excretory matter are often to be detected in the protoplasm.
Among these larger cells are often intercalated gland cells, which
appear to secrete a digestive fluid. Ganglion cells and pigment cells
occur; but though nematocysts have been detected in endoderm
cells, it is still doubtful whether they are formed in them
or not.

Where they form the axial core of a solid tentacle, the endoderm
cells become vacuolated and ‘‘cartilaginous” in consistence, re-
sembling the notochordal cells of Chordata (Fig. 10).

The mesogloea forms a thin lamina everywhere between ectoderm
and endoderm cells and gives by its stiffness a certain rigidity to
the body. It is often apparently laminated. Although itself in-
capable of contraction, it is greatly thickened and shortened, on the
contraction of the body, by the muscular fibres of the ectoderm and
endoderm.

HISTOLOGY OF THE MEepDuSoID.—The ectoderm appears over the
greater part of the umbrella as a layer of much flattened cells, but
is cubical on the velum and manubrium. £pithelio-muscular cells,
like those of the hydroid, occur also in the medusoid, but sub-
epithelial muscle cells are here more common; they are either
scattered, or grouped in trabeculae, and in some cases become em-
bedded in the mesogloea. The ectodermal muscle fibres may have
either a circular or longitudinal trend, unlike those of the hydroid.
On the manubrium cir-
cular musculature is
well developed; longi-
tudinal fibres also occur
on it, which are con-
tinued centrifugally out-
wards, radiating over
the subumbral surface

Fic. 10a.—Muscular cells of medusae (Lizzia). The towards the lip of the
biceeemions is a purely muscular cell from the subumbrella ; bell. The subumbrella
sie ro ewer aro oplthalioanneceia: walls es the eee SGA ale cee

the epidermal mosaic on the free surface of the body. fibres ; the exumbrella
(From Lankester, after Hertwig.) A

has little or no museu-
lature. Strongly developed circular fibres characterise the edge
of the bell and the velum ; by their agency the contraction and con-
sequent progression of the bell are chiefly effected. The tentacles
are highly contractile, and are provided with strong longitudinal
muscles. Sensory cells, which are elongated and columnar, and are
provided with palpocils, are well developed at the bases of the

_

THE HYDROMEDUSAE 9

tentacles. Subepithelial ganglion cells and nerve fibrillae form a
scattered plexus in the ectoderm in connection with sensory and
muscle cells, especially on

the subumbrella ; they are ce a
concentrated at the lip of ei ae
the bell into a nerve ring, Tf
which is divided by the LY
insertion of the velum into K—~f
outer and inner portions, a) Lae
connected by nerve fibrils Se
through the mesogloea. ° —<t
Connected with the —
nerve ring are the sense SS
organs (Hertwig, 19 ; Eimer,
20) or special aggregations
of sense cells. They are
referable to four chief - Sr ee
types. Fic. 10).—Scattered nerve-ganglion cells from the

1. Ocelli or eye spots ae of Aurelia. (From Lankester, after
are generally found at the
bases of tentacles. In their simplest form they consist of a few
_ sense cells between which are scattered a few pigment cells ; in their
complete development, the sensory and pigment cells are grouped
into a definite organ of subspherical shape (Fig. 11), which projects
above the general surface, and may secrete a cuticular lens (Lizzia).
The whole structure is ectodermal.

2. Otocysts are found under two chief forms: (a) in the simpler
of these the organ consists of an open subumbral pit at the base
of the velum, the cells of which secrete each an otolith of organic
and calcareous nature (Mitrocoma) ; () in the more complex type
the pit becomes converted into a closed vesicle, containing one or
more otolithic cells, which are usually supported on sensory hairs.
The whole structure is ectodermal, and may occur either on or
between tentacles (Figs. 12, 13).

3. Cordyli (Brooks, 21) are exumbral structures, placed between
tentacles, which consist of a core of vacuolated endoderm cells
covered by flattened ectoderm. It is possible that they represent
a modification of a tentacle, less complete than, but analogous to,
the modification which has produced the next form of Hydro-
medusan sense organ (Fig. 15).

4. Tentaculocysts, which are apparently tentacles modified for
the better perception of auditory vibrations, and are placed exum-
brally, consist essentially of a club-shaped structure, clothed extern-
* ally by ectoderm ; they contain an axial core of endoderm cells, the
- outermost (one or more) of which secretes an otolith. The club
thus formed either projects freely from an eminence composed of

15

10 THE HYDROMEDUSAE

fOTOLOT é Yolels s

<6/01g ey i oa @ sf

11.—Ocellus of Lizzia Koellikeri. oc, pigmented ectodermal cells; J, lens.

12.—Otocyst of Phialidiwm. di, superficial layer of ectoderm ; d2, deep layer of ecto-
derm ; h, auditory cells of ectoderm ; hh, auditory hairs; mp, nerve body; mrl, upper nerve
ring; 7, endoderm cells of the circular canal. The otolith cavity is seen above h. (Figs.
11, 12, from Lankester, after Hertwig.)

13.—Otocyst of Euchilota, 0, otolith ; remaining letters as Fig. 12. (After Hertwig.)

14.—Simple tentaculocyst of one of the Trachomedusae (Rhopalonema velatum). The process
carrying the otolith or concretion Ak, formed by endoderm cells, is enclosed by an upgrowth
forming the ‘‘ vesicle,” which is not yet quite closed in. (From Lankester, after Hertwig.)

15.—Optical section of a cordylus or sense club; the surrounding structures are only
roughly indicated. CC, circular canal; EU, exumbral surface; Me, mesogloea ; NR, the
outer, NR’, the inner parts of the nerve ring; SU, subumbral surface; 7, tentacle; V,
velum. (After Brooks.)

THE. HYDROMEDUSAE II

sensory cells provided with long sensory hairs (Cunina), or becomes
surrounded by a closed vesicle, a stage in the formation of which
is shown in Fig. 14; the club is supported in position by
long sense hairs, and the vesicle filled with fluid (Rhopalonema).
The endoderm, in secreting the otolith, has here a definite sen-
sory function, which is confined to the ectoderm in ocelli and
otocysts.

Gland cells, pigment cells, cnidoblasts, and supporting or interstitial
cells are of constant occurrence ; the cnidoblasts are especially well
developed on the tentacles.

The endoderm has much the same characters as in the hydroid.
The mesogloea is often extremely thick, especially on the exumbral
surface. Although it is essentially a non-cellular layer, but is
rather an inert secretion by ectoderm and endoderm, when well
developed, it often contains amoeboid wandering cells (Fig. 85), and
elongated muscle cells, both in all probability migrants from the
ectoderm. It is firm and jelly-like, and often shows a fibrillated
structure.

The ova and spermatozoa are, with rare exceptions, of the
type usual in the Animal Kingdom.

ORDER 1. Anthomedusae (Gymmnoblastea).

DEFINITION.—Hydromedusae with a regular alternation (meta-
genesis) of a sterile hydroid generation with a sexual generation
of medusoids or other gonophores. The perisare does not form
hydrothecae into which the hydroids are completely retractile, nor
rigid permanent gonothecae. The sense organs of the medusoids
are ocelli. The generative organs lie in the wall of the
manubrium.

The Hyproip is colonial and fixed (Bougainvillea) ; or is non-
colonial, and then is either fixed (Myriothela) or free (Hydra).
The hypostome is conical or truncated, rarely trumpet-shaped
(Eudendrium). The tentacles are hollow (Hydra) or, more usually,
solid (Bougainvillea) ; they are rarely absent (Microhydra). They
are irregularly scattered (Hydra), or form a circlet (Bougainvillea),
or even two circlets (Tubularia) round the mouth. They never
have a pore at the tip, and are rarely branched (Cladocoryne) or
webbed. They are filiform (Hydra) or capitate (Coryne); in
the former case the nematocysts are chiefly concentrated in
scattered wart-like batteries; in the latter case in the head.
The coelenteron of the hydroid is sometimes nearly divided into

_ two by a constriction (Tubularia). Lobes (Tubularia) or villi
(Myriothela) may project into it from the body wall.

A hydrorhiza (Figs. 16 to 20) is generally more or less

developed in the fixed forms, whether single (Myriothela) or

12 THE HYDROMEDUSAE

wos ee ee eee
colonial (Bougainvillea); but may be replaced by filiform pro-
cesses (Corymorpha); it is, of course, absent in the motile
forms (Hydra). In the colonial forms it gives rise to one or
more simple (Perigonimus) or branching (Bougainvillea) hydrocauli.
The coenosare of both hydrocaulus and hydrorhiza generally forms

a single tube.

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Fic. 17.

Fic. 16,
jossible modifications of persons of a Gymnoblastic Hydromedusa.
coelenteron ; d, endoderm (thick black line);

16.—Diagram showing }
hydroid expanded ; g’, hydroid con-

a, hydrocaulus (stem); 6, hydrorhiza (root); ¢,
e, ectoderm (hatched); f, perisare (thin black line); g,
tracted; h, hypostome, bearing mouth at its extremity ; k, degenerate medusoid (sporosac)
springing from the hydrocaulus ; k’, sporosac springing from m, a moditied hydroid (blastostyle) ;
the genitalia are seen surrounding the spadix ; /, medusoid ; m, blastostyle. (After Allman.) .
17.—Diagram showing possible modifications of the persons of a Calyptoblastic Hydro- |
medusa. Letters a to k same as in Fig. 16. 7, the horny cup or hydrotheca of the hydroid ; J, |
medusoid springing from m, a modified hydroid (blastostyle); n, the horny case or gonotheca
enclosing the blastostyle and its buds. This and the hydrotheca i give origin to the name
Calyptoblastea. (After Allman.)
,

The tubes of the hydrorhiza are generally distinct from one
another, although they are often connected by cross-tubes into a .
loose meshwork. In Podocoryne, however, such a meshwork occurs
only at the growing points of the colony ; in the more central parts .
the tubes increase in number and anastomose so freely as to appear |

==

THE HYDROMEDUSAE 13

to form a solid crust ; this crust is in reality composed of separate
coenosareal tubes, each surrounded by perisare. If, instead of the
perisare of adjacent tubes becoming adherent or continuous, its
formation were suspended until the ectoderm of adjacent tubes had
become confluent, we should
arrive at the condition presented
by the central parts of Hydrac-
tinia (Colleutt, 26); towards the
edge of the colony this genus
has the same structure as the
central parts of Podocoryne ; at
the growing edge both have a
loose hydrorhiza of the usual
type.

The tubes of the hydro-
caulus are generally distinct,
but in some cases the stem of
the colony is ‘‘fascicled” or
formed of closely apposed or
adherent hydrocauli (Euden-
drium). Just as this is a modi-
fication comparable to the ad-
herent hydrorhizal tubes of
Podocoryne, so the confluent Fic. 18.—Colony of Bougainvillea (nat, size)

attached to a piece of floating timber. (After
ectoderm of numerous hydro- jiman.)
cauli in Ceratella (Spencer, 27)
is comparable to the central hydrorhiza of Hydractinia. <A
further complication is introduced in the hydrocaulus of Cory-
dendrium, owing to the fact that the young buds, instead of
breaking through the perisare and growing outwards as is usual,
grow upwards for some distance inside it and surround them-
selves by secondary perisare (Weismann, 10).

A space generally lies between the ectoderm, and the perisare
of hydrocaulus or hydrorhiza which it secreted ; strands of proto-
plasm or elongated ectoderm cells may cross this space.

The perisare is rarely absent (Hydra) ; it generally forms a com-
plete investment of hydrorhiza and hydrocaulus, and is sometimes
prolonged over the body of the hydroid as a sort of hydrotheca (some
Bougainvillea), into which the entire hydroid cannot be withdrawn.
The perisare is generally a cuticular secretion of a horny character,
but may be formed of adventitious particles held together by a
secretion (Perigonimus) ; in both cases the secretion is formed by the
activity of the ectoderm cells. A horny perisare is usually smooth,
but may be annulated at the origin of each branch (Cordylophora)
or uniformly annulated throughout its length (Coryne). A horny
perisare generally exhibits a concentrically laminated structure,

14 THE HYDROMEDUSAE

and can be thickened by the addition of layers from without
inwards. It can be reabsorbed by the agency of the ectoderm
cells which secreted it; this occurs when a new bud grows out-
wards from the coenosare.

POLYMORPHIC MODIFICATIONS OF THE Hyproip.—A Jlastostyle
(Fig. 16, m) is a hydroid which exhibits a greater or less simplifica-
tion of structure, in correlation with its special function of giving
origin to medusoids by budding. It may have a few small tentacles

Fic. 19.—Portion of colony of Bougainvillea magnified.
(From Lubbock, after Allman.)

(Podocoryne), or the tentacles may be reduced to mere knobs
(Hydractinia, Fig. 22, >) or absent (Eudendrium). The mouth is
very small or absent. There seems to be no reason to deny the
name blastostyle to the elongated tubes which spring from the
hydroid of Tubularia, each of which buds numerous medusoids
(Fig. 24, 4). The blastostyle may spring from the hydrorhiza
(Podocoryne), from the hydrocaulus (most Eudendrium), or from
the hydroid (Tubularia).

A false blastostyle (Allman, 1 ; Weismann, 10) is formed by the

THE HYDROMEDUSAE 15

20.—Part of colony of Perigonimus ; the thin perisare
not shown. The zooids spring from a hydrorhiza. a,
hydroids in different phases of expansion; }, developing
hydroid; c, stages in development of medusoid; d, free
medusoid. (After Allman.)

21.—Diagram of Clava, showing a hydroid surrounded
by a verticil of degenerate medusiform persons (sporosacs).
(After Allman.)

22.—Diagram of Hydractinia, showing four forms of
persons. @, hydroid; b, modified hydroid, or blastostyle,

_ bearing c, degenerate medusiform persons or sporosacs ;
d, modified hydroid situated at the margin of the colony
(dactylozooid). (After Allman.)

7 23.—Diagram of Corymorpha, a hydroid with a double
circlet of tentacles. A, the hydroid; b, medusoids, Pe
budded on its dise. 2B, the free medusoid, with one Fig. 23.
tentacle ; the generative cells are indicated in the wall of
the manubrium. (After Allman.)

16 THE HYDROMEDUSAE

absorption of the tentacles and the diminution in length of an
ordinary hydroid which has begun to bud medusoids (Euden-
drium).

A dactylozooid is a hydroid which exhibits modifications corre-
lated with its special functions of catching prey. It is elongated,
and capable of very active movements, and is either devoid of
tentacles (Podocoryne), or provided with short knobs highly
charged with nematocysts (Hydractinia, Fig. 22, d). The cnido-
phore of Eudendrium racemosum appears to belong to the
category of dactylozooids, from which it differs merely in grow-
ing from the body of a hydroid, and not from the hydrorhiza
(Weismann, 10).

The MEDuSOID (Fig. 25) is generally conical or hemispherical,
in contrast to the next order; the velum is broad and muscular.
The manubrium is generally circular ; the mouth is sometimes sur-
rounded by four perradial lobes (Tiara) or four simple or branching
capitate “oral tentacles” (Bougainvillea). The marginal fentacles are
rarely rudimentary (Amalthea) ; when present they are generally
hollow ; they number one (Cory-
morpha), two (Perigonimus), or
six (Clavatella), but are gener-
ally only four in number and
placed at the ends of the per-
radial canals. Interradial ten-
tacles may also be present
(Podocoryne), or very numerous
tentacles arranged in four per-
radial groups (Bougainvillea) ;
even hundreds may be present
(Callitiara), arranged apparently
without reference to special
radii. Their bases are generally

Fic. 24.—Diagram of Tubwaria. b, degenerate surrounded by a thickened bulb
ny budded from a blastostyle. (After of ectoderm, containing sensory
cells and numerous cnidoblasts.

The sense organs of the Anthomedusae are ocelli. These consist
either of a few pigment cells, hardly grouped into an organ
(Euphysa), or of pigment cells grouped into a definite retina,
which possesses (Lizzia, Fig. 11) or lacks (Sarsia) a lens.

They are placed on the bulb of the tentacle, and are generally
on its exumbral face, but are on the subumbral face in genera
which normally carry their tentacles reflexed (Lizzia).

The gastric cavity generally lies in the bell, but may be
situated at the root of the manubrium (Lar). It often exhibits
a prolongation upwards into the substance of the mesogloea of the
exumbrella, a relic of the endoderm of the coenosarcal tube by

THE HYDROMEDUSAE 17

which its coelenteron originally communicated with that of the
colony from which it was budded.

The radial canals are generally four in number, and are then
perradial ; but four interradial canals are also developed in some
cases (Cladonema). Six are normally presented by Clavatella
(=Eleutheria). In Lar (= Willsia) six are also present, which
bifurcate twice; there are thus twenty-four openings into the
circular canal.

The generative cells (gonads) lie in the wall of the manubrium,
between the ectoderm and the mesogloea, or in the ectoderm itself ;
they rarely reach on to the subumbrella (Nemopsis). They are

Fic. 25.
Diagrams of the medusoids of two species of ‘‘ Sarsia,” the one budding medusoids from the
manubrium, the other from the ends of the radial canals. (After Allman.)
cylindrically arranged (Sar sia), or are broken up into four or eight
bands. In Lar they are six in number, and lie on the walls of the
six-rayed gastric cavity inthe manubrium. The sexes are separate.
FORMATION OF THE MEDUSOID BY GEMMATION.—A medusoid
of the type indicated above is either budded (a) from a hydroid
(Syncoryne), or from a blastostyle (Tubularia), or from the
hydrocaulus (Bougainvillea), or, with the intermediation of a
short stem, from the hydrorhiza (most Perigonimus), or (/) from a
medusoid (Sarsia), either from the manubrium (Fig. 25), or
from the margin of the bell, at the end of the perradial canals
(Codonium). Although in many cases medusoids have not been
traced to hydroids, no medusoid of this group has been found
to develop directly from the ovum.

3

18 THE HYDROMEDUSAE

If, as seems probable, the product of the fertilised ovum of
the Anthomedusae is always a hydroid, there is an invariable
alternation of an asexual generation (the hydroid) with a sexual
generation (the medusoid); this alternation of generations, or
metagenesis (Brooks, 14), is not disturbed by the fact that the sexual
generation may in a few cases reproduce asexually (Sarsia),

Ctenaria Ctenophora (Haeckel), one of the Anthomedusae, presenting a curious resem-
lance to the Ctenophora. <A, lateral view of the entire medusa; 3B, two horizontal views,
that to the left representing the surface of the aboral hemisphere, that to the right a section
passing nearly equatorially. «, the eight adradial rows of thread cells, corresponding
in position to the eight ctenophoral zones of Pleurobrachia; b, jelly of the umbrella;
¢, circular muscle of the subumbrella; d, longitudinal muscles of the subumbrella; e,
stomachal dilatation of the enteric cavity; /, the sixteen oral tentacles; g, the four perradial
generative glands in the stomach wall (manubrium); /, the four perradial primary radiating
canals ; i, the eight adradial bifurcations of the preceding; k, ring canal in the margin of the
umbrella; 1, velum; m, the two lateral tentacle pouches; , the two lateral unilaterally
fringed tentacles; 0, the apical gastric cavity above the stomach. The canal system,
with its four primary and eight secondary rami, resembles that of Pleurobrachia. The mouth
of the latter may be homologous with the margin of the umbrella of the former, and the mouth
of Ctenaria homologous with the junction of the so-called funnel of Pleurobrachia with its
so-called digestive cavity. This last may be the homologue of the subumbrellar cavity of
Ctenaria. The apical opening or openings of the funnel of Ctenophora suggest the stalk canal
of medusae, whilst the agreement between the tentacles and their pouches in Ctenaria and
Pleurobrachia is complete. Cf. p. 14, infra. (After Haeckel.)

The method of formation of a medusoid (Weismann, 10) varies
in detail in different genera, but the following account of Bougain-
villea may be taken as typical. A rapid proliferation of cells at
the apex of a simple bud (Fig. 27, I) results in the production of
a lens-shaped mass of cells ; this sinks below the level of the super-
ficial ectoderm, pressing the endodermal wall in front of it into
the shape of a cup. This mass of ectoderm is termed the ento-

THE HYDROMEDUSAE 19

codon, and a cavity which appears in its interior is the rudiment
of the subumbral cavity (Fig. 27, II). It is followed by an in-
vagination of the superficial ectoderm, between which and itself
mesogloea is deposited ; the wall between the two cavities is the
future velum (Fig. 27, III). Growth of the subumbral cavity
results in an approximation of the endodermal walls of the coelen-
teron; they ultimately fuse into an endodermal lamella (Fig. 27, IV)
except where the circular and radial canals are to lie (Fig. 6). An
upgrowth of the manubrium from the floor of the subumbral
cavity, the formation of the tentacles, and the perforation of

4,
[2
‘\)

—ea(o)
Fic. 29.

SIM

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2

‘ 4,
-
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BOK) E
aD
mite
a ee

Fic. 27.

27.—Diagrams of sections of four stages in the development of a medusoid by gemma-
tion. I. The original bud of ectoderm, mesogloea, and endoderm. II. The entocodon has
been formed; a cavity—the future subumbral cavity—has appeared in its interior; it has
pressed the endoderm into the shape of a cup. elII. The growth of the entocodon inwards is
followed by an invagination of ectoderm, the wall between the two is the future velum. IV.
The entocodon has formed the subumbral cavity, the manubrium projects upwards into it.
The thin walls of the bell show a radial canal on the right side (perradial section), and the
gastral lamella on the left side (adradial section). A solid tentacle is forming at the base of
the radial canal. The thin layer of perisare has been omitted. C, coelenteron ; CC, circular
canal; GL, gastral lamella; MW, manubrium; &C, radial canal; SU, entocodon = subumbral
cavity ; T, tentacle; V, velum.

28.—Diagram of half-section of sporosac of male Eudendrium, showing from without
inwards ectoderm, spermatozoa, mesogloea, endoderm lining coelenteron.

29.—Diagram of half-section of sporosac of female Cordylophora, showing gelatinous layer,
ectoderm, ova lying among coelenteric tubes of mesogloea and endoderm.

velum and manubrium, complete the essential formation of the
medusoid ; a constricting ingrowth at the attached end results in
the separation of the medusoid from the parent.

Medusoids are essentially devoted to the carriage of the
generative cells and the dissemination of the species ; the latter is
achieved by the free-swimming or floating habit of the organism,
which is rarely known to creep, temporarily (Cladonema) or per-
manently (Clavatella).

20 THE HYDROMEDUSAE

POLYMORPHIC MODIFICATIONS OF THE MeEpusoipD.—In many
cases the gonophore, or bearer of the generative cells, has not the
complicated structure of the medusoid, but one far simpler; the
simpler conditions are probably not phases in the evolution of a
more complex type, but, contrariwise, have been attained by the
reduction of the higher organisation. Every stage in this process
of simplification is represented among the Anthomedusae, until in
Hydra, the final term of the series, nothing remains of the highly
organised medusoid except the generative cells. The following
types (Weismann, 10) indicate the gradual abandonment of com-
plexity of structure :—

1. The gonophore has the general form of a medusoid, but is
never freed. The ocelli are always wanting, the velum and mouth
generally, the tentacles sometimes; but the subumbral cavity,
the manubrium, and the radial canals are developed (Tubularia).
2. The gonophore is arrested at an early stage in the development
of the medusoid, corresponding roughly to Fig. 27, II]. The ento-
codon and subumbral cavity are developed, but the latter never
opens to the exterior, and no radial canals are traceable. The manu-
brium is only slightly indicated (male Clava). 3. The gonophore
develops no entocodon. (a) In some cases the endoderm lamella
is nevertheless formed, combined with a few immigrant ectoderm
cells (Coryne); () in other cases the endoderm lamella is not
developed, and a section to the centre shows merely ectoderm,
generative cells, mesogloea, endoderm lining coelenteron (Fig. 28).
This type of gonophore is termed a sporosac, and is very commonly
found among Anthomedusae. The endodermal core (sometimes
termed the spadix) may be straight (male Eudendrium, in which
the sporosac is ampullated), or may be curved round the
generative cells (female Eudendrium), or form anastomosing
branches (Cordylophora, Fig. 29). 4. The generative cells are
developed in the ectoderm of the body of the hydroid, and no
trace of a medusoid is recognisable (Hydra, Fig. 3).

In a few instances a thin and temporary gelatinous capsule
invests the gonophore, whether a medusoid (Bougainvillea) or a
sporosac (Cordylophora).

ORIGIN OF THE GENERATIVE CELLS.—Approximately parallel
to these modifications, and probably correlated with them, is a
gradual alteration in position of the spot at which the generative
cells are differentiated in various genera; this is apparently
attributable to a necessity for the production and maturation of
these cells as early as possible, and may be termed a process of
acceleration. In the medusoid the generative cells are both formed,
and ripen, in the manubrium ; in the first stage of acceleration they
are formed in the entocodon, and ripen in that part of it which
ultimately becomes the manubrium (Tubularia). In the second

THE HYDROMEDUSAE 21

stage they appear in the bud of the gonophore at an early phase
of its development; in the female Podocoryne, for instance, they
have been first noticed in the endoderm of the bud, and migrate
into the ectoderm of the manubrium through the mesogloea; in
Coryne, where no entocodon is formed, they both appear and ripen
in the endoderm of the sporosac. In the third stage they first
appear in the tissues of the hydroid, blastostyle, coenosare, or
hydrorhiza, from which the gonophore will ultimately be budded ;
in Hydractinia, for example, they are first noticeable in the ectoderm
of the blastostyle (Colleutt, 26), and migrate along the endoderm
into the sporosac, breaking through the mesogloea to ripen in the
ectoderm. In the female Eudendrium racemosum their wanderings
are still more complex. They are formed in the ectoderm of a main
hydroid, migrate into the ectoderm of a lateral hydroid, thence
into the endoderm, first of the blastostyle, then of the sporosac,
and ultimately break through into the ectoderm of the sporosac.
Although in many cases the generative cells are only recognisable
for the first time in the endoderm, it is probable that they are
in all cases originally ectodermal cells, which may or may not
migrate into the endoderm ; in almost every instance they ripen in
the ectoderm. The whole question is dealt with by Weismann
(10).

There is thus evidence that a marked change is in progress
among the Anthomedusae; the alternation of the fixed nutritive
hydroid with the sexual free-swimming medusoid is being gradually
abandoned ; the medusoid, the function of which was to form,
ripen, and disseminate the generative cells, is being replaced by the
sporosac, in which they merely ripen ; their formation is becoming
a function of the colony or of the hydroid. Curiously enough, in
one genus, Dicoryne, which forms sporosacs of the simplest type
on a blastostyle, there occurs an apparent reversion to the old
method of dispersal of the species, for the sporosac becomes con-
stricted off from the blastostyle, and swims freely by means of
strong cilia (Allman, 1).

ASEXUAL REPRODUCTION. — In gemmation, which is the rule
among hydroids, both ectoderm and endoderm form a hollow lateral
protrusion of the body or coenosare ; this absorbs a window in the
perisarc where necessary, and either by the development of mouth
and tentacles becomes a new hydroid, or in the manner already
sketched (pp. 18, 19) is converted into a medusoid or a sporosac.

Gemmation from a medusoid appears to be of a similar
“laminar ” character, and to follow the lines sketched on pp. 18, 19 ;
its product is always a medusoid.

Fission is rare among hydroids ; it may be transverse (Pro.
tohydra) or longitudinal (Polypodium). It has not been shown to
occur among medusoids in this group.

22 THE HYDROMEDUSAE

SEXUAL REpRODUCTION.—As a rule the female generative cells
(ova) and the male cells (spermatozoa) are formed in different
colonies ; they sometimes occur on different individuals of the same
colony (Dicoryne), or on the same blastostyle (Myriothela) ; they
rarely occur in the same individual (Hydra).

In some cases there is but one ovwm in each gonophore
(Eudendrium) ; more commonly, one cell at a time, out of many
“potential ova,” is fertilised and develops, the remainder serving
as its food (Tubularia). The spermatozoa are always extremely
numerous. They escape by rupture of the tissues of the parent,
and swim freely in the water. In most medusoids the ova are
discharged in the same manner; in most sporosacs and sessile
gonophores the ova are fertilised by spermatozoa, which penetrate
to them through the tissues. Segmentation of the ovum generally
produces a dlastula (Fig. 1), a larva consisting of a single layer of
cells arranged round a central cavity, the Dlastocoele. By karyo-
kinetic cell division ‘fresh cells are budded from the outer
layer into the blastocoele, which they ultimately obliterate. This
process is the formation of a diblastula (gastrula) by delamination
(Fig. 2); the outer cells are the future ectoderm, the inner mass
will give rise to the endoderm. The ectoderm becomes ciliated, the
diblastula elongates into the larval form termed a planula,; at this
stage it generally leaves the parent and swims freely in search of
an appropriate site. To this it affixes itself, and sends out rooting
processes (hydrorhiza). A coelenteron becomes excavated in its
interior; and the appearance of mouth and tentacles, and the
differentiation of cell forms, convert it into a hydroid. In some
cases the larva is not freed from the parent till this stage (actinula-
larva of Tubularia). In Hydra the ectoderm of the diblastula
secretes horny protective coatings, in which it passes a long
resting stage at the bottom of a pond; a ciliated planula stage
does not occur in its history.

In some cases the planula, instead of developing mouth and
tentacles, grows after fixation into a branching hydrorhiza, and
gives origin to hydroids by gemmation (Mitrocoma—Metschnikoff,
13).

ORDER 2. Leptomedusae (Calyptoblastea).

DeEFINITION.—Hydromedusae with a regular alternation (meta-
genesis) of a sterile hydroid generation with a sexual generation
of medusoids or other gonophores. The perisare typically forms
hydrothecae into which the hydroids are completely retractile, and
rigid permanent gonothecae which completely envelop the blasto-
styles and gonophores. The chief sense organs of the medusoids
are ocelli and otocysts; the otoliths are the products of ectoderm
cells. The generative organs lie on the radial canals.

THE HYDROMEDUSAE 23

The HYDROID is generally colonial, and has a trumpet-shaped
hypostome. The tentacles form a single circlet; they have a solid
endodermal axis, and are filiform; they are rarely webbed (Cam-
panularia flexuosa). The hydrorhiza is generally well developed and
gives origin to simple (Lafoea) or branching (Obelia) hydrocauli.
The tubes of the Aydrocaulus are generally distinct from one another
(monosiphonic) ; but several hydrocauli, each bearing hydroids or
branches, may be closely bound into a compound or polysiphonic
stem with greater or less confluence of the ectoderm (Aglaophenia).
The hydrocaulus may be strengthened by the apposition of a second
hydrocaulus which bears no hydroids, the perisare of the two being
continuous, except for occasional points at which the ectoderm of
the two becomes confluent (Anisicola halecioides—Jickeli, 31).

Very exceptionally, numerous hydrocauli may be clustered
round a central hydrocaulus ; of these the central one gives origin
to the hydroids and to the smaller branches ; the accessory ones
communicate occasionally with each other and with the central
one, and give origin to the nematophores (Plumularia procumbens).
A still more complex and unique condition, but one apparently
deducible from the last instance, is presented by Clathrozoon ; the
accessory hydrocauli, surrounded by perisarc, anastomose so freely
that each stem appears to be made up of a mass of irregularly
branching tubes, several of which communicate with the coelenteron
of each hydroid. This arrangement at first sight suggests an
Alcyonarian or a perforate Madreporarian rather than a Hydro-
medusan (Spencer, 32).

A perisarc is always present as a complete investment of
hydrorhiza and hydrocaulus ; it generally has the same substance
and structure as in Anthomedusae. It almost invariably ex-
pands at the base of each hydroid as a rigid hydrotheca, of variable
form in different genera, into which the entire hydroid can with-
draw itself (Figs. 30, 31); this is occasionally absent (Cam-
panopsis).

The edge of the hydrotheca is often toothed ; on the retraction
of the hydroid, these teeth may fold inwards to form a conical
operculum which closes the orifice of the hydrotheca (Calycella).
There is sometimes only a single plate serving as operculum
(Diphasia), or none at all (Halecium).

The hydrocaulus may carry only one hydrotheca (Clytia) ;
more commonly it bears a large number ; it may give off branches
(rami, pinnae), on which the hydroids are borne; or the rami
may bear branchlets (ramuli, hydrocladia) to which the hydroids
. are limited. Hydroids are occasionally borne on a_blastostyle

which carries also a medusoid (female Halecium).

The hydroids and hydrotheca are often confined to one plane
on the branch, lying either on one side only of the hydrocaulus

a

24 THE HYDROMEDUSAE

(Plumularia), or both sides ; in the latter case, the hydroids lie in
pairs, right and left, opposite to one another (Diphasia), or lie
singly, alternating on right and left sides (Obelia). They are
stalked (Obelia), or sessile on the hydrocaulus (Plumularia), The
perisare of hydrocaulus and hydrotheca may be either smooth or
annulated. While in the Anthomedusae the topmost hydroid of a
stem or branch is the oldest, and buds the remainder of the hydroids
(or branches) laterally, in the Leptomedusae the formation of new
hydroids takes place at the apex of each branch, and the topmost
hydroid is therefore the youngest.

POLYMORPHIC MODIFICATIONS OF THE HypRoID.—A Jlastostyle is
very commonly developed, which is devoid of mouth and tentacles ;
the ectoderm at its apex is generally thickened into a special
organ, the opercular plate (Figs. 35, 36). Dactylozooids are re-
presented in this group by the nematophores (machopolyps), specially
modified hydroids provided with hydrothecae (Fig. 30). They are
occasionally much elongated and capitate, growing out for some
distance from hydrocaulus and hydrorhiza (Ophiodes) ; but more
commonly they are short and nearly sessile. In many cases two
are placed above each hydroid, and one below it (Aglaophenia,
Fig. 31); sometimes they are scattered without symmetrical refer-
ence to the hydroids (Plumularia), and are often specially concen-
trated round the gonophores (Aglaophenia). They are tentacle-like,
with a solid endodermal axis, and are generally provided with a
capitulum of cnidoblasts (Plumularia); but in some cases the
cnidoblasts are replaced by cells which secrete adhesive globules.
When both enidoblasts and adhesive globules occur in the same
species, only the nematophores with cnidoblasts are advanced when
the colony is disturbed ; when undisturbed only those which form
adhesive globules are protruded (von Lendenfeld, 33 ; Wagner, 29).

The MEDUSOID (Figs. 32, 33) is generally much flatter than
in the Anthomedusae, its bell less rigid, and its velum smaller
and weaker. The manubrium is generally short, rarely absent
(Staurostoma) ; the mouth is usually four-lobed, but very numerous
accessory lobes are sometimes developed (Polycanna).

The marginal tentacles are as a rule hollow, rarely solid (Obelia).
There may be but two of them (Dissonema) ; generally they are
four in number, and perradial in position, or become eight in
number on the addition of four interradial tentacles (Eucope).
They may increase in number with radial regularity until they
amount to hundreds (Aequorea). Their bases are usually expanded
into a bulb like those of Anthomedusae.

Among the marginal tentacles are placed in many cases
marginal cirrhi, which are shorter than the tentacles, and have a
solid endodermal axis (Laodice). They are highly contractile,
often coiled spirally, and provided with a terminal battery of

THE HYDROMEDUSAE 2

vi

enidoblasts. On the outer edge of the bell are also found in some

Fia. 30. Fic, 31. Fig. 34.

80.—Small portion of a hydrocladium of a Plumularian hydroid. Between two annulations
of the hydrocladium lie (a) a hydroid projecting from its hydrotheca; (6) above it two
lateral nematophores (modified hydroids), one of which is expanded; (c) below it a single
median nematophore, also expanded, and spreading over the hydrotheca. (After Allman.)

31.—Perisarc of a small portion of a hydrocladium of Aglaophenia filicula, viewed at right
angles to the plane of Fig. 30, showing between each two annulations of the hydrocladium, one
hydrotheca, two lateral and one median semitubular thecae for nematophores. (After Allman.)

$2.—Diagram of the flattened medusoid of Obelia, showing two of the four perradial canals
with the pendent gonads, four of the eight adradial otocysts.

83.—View of the oral surface of one of the Leptomedusae (Jrene pellucida, Haeckel), to
show the numerous tentacles and the otocysts. ge, genital glands ; M, manubrium ; ot, otocysts ;
ve, the four radiating canals; Ve, the velum. (From Lankester.)

84.—Part of the edge of the bell of a Leptomedusan. CC, circular canal; MC, marginal
cirrhus; MF, marginal funnel; M7’, marginal tubercle; RC, opening of radial into circular
canal; 7’, tentacle (cut short); V, velum. (Modified from Haeckel.)

genera marginal tubercles, slight prominences on the body wall,
generally containing a prolongation of the coelenteron, often
16

26 THE HYDROMEDUSAE

pigmented and provided with cnidoblasts (Octorchis). They are
often placed opposite to the marginal funnels (subumbral papillae),
which lie on the subumbral surface above the velum; these are
conical prominences with an excretory pore at the apex, through
which fluid has been seen to be ejected from the circular canal
(Octorchis). These three structures are shown in Fig. 34.

The sense organs are ocelli, otocysts (marginal vesicles), and
cordyli (marginal clubs); their arrangement has been utilised for
purposes of classification.

The ocelli are generally placed on the tentacle bulbs, but may
occur also at the bases of the marginal cirrhi, or of the cordyli; they
may be dotted, in number several hundreds, along the margin of
the bell (Orchistoma). They are rarely provided with a lens.

The otocysts are placed at the base of the velum; they are at
least eight in number, and are then adradial in position (Obelia).
They are often numerous, and may be reckoned by hundreds
(Polycanna). The cordyli are indefinitely scattered, and are
generally numerous.

The gastric cavity is simple, and is excavated in the bell. The
vadial canals are often four in number, and perradial in position
(Eucope) ; to these four interradial canals may be added (Meli-
certum) ; fresh canals may be added till the number amounts to
about 200 (Orchistoma). The canals occasionally branch after
leaving the gastric cavity ; in this case only the perradial canals
may reach the circular canal, the branches ending blindly (Stauro-
discus); or the branches also may open into the circular canal
(Berenice).

The generative cells in the medusoid lie on the subumbral wall
of the radial canals, rarely reaching back to the gastric cavity or
on to the manubrium. They form either one central, or two
lateral flat bands along the course of the canal (Fig. 33) ; or in many
cases lie in special pouches on the canals (Fig. 32). They occur
on the four perradial canals, or on both perradial and interradial
canals ; in species with branching radial canals they may lie on the
branches also. As in the Anthomedusae, they are placed between —
the ectoderm and the mesogloea, or in the ectoderm itself. The
sexes are separate.

The method of FORMATION OF THE MEDUSOID is of the type
already described in Anthomedusae. The medusoid may be budded
from the hydrocaulus (Campanulina) or, more commonly, from a
blastostyle. Although even fewer medusoids have been traced to
their hydroids in this group than in the Anthomedusae, no
medusoid has been observed to develop directly from the ovum,
and it is probable that a regular alternation of generations or
metagenesis is the invariable rule.

PoLyMorPHIC MODIFICATIONS OF THE MEDUSOID.—The simpli-

THE HYDROMEDUSAE 27

fication of the gonophore, the reduction of the high organisation of
the free-swimming medusoid, is as noticeable in the Leptomedusae
as in the Anthomedusae.

1, The gonophore retains certain medusoid structures, such as
the radial and circular canals and the tentacles, but the mouth
is never perforated, and the organism never freed (Gonothyraea).
In this, and in many far simpler gonophores of the Leptomedusae,
the ectoderm of the blastostyle is multilaminar; the inner
layer gives rise to the entocodon and the exumbral ectoderm
of the gonophore; the outer layers, separated from the inner by
a space, form a more or less complete sheath of the gonophores, and
appear also as irregular strands (gubernaculum, Fig. 36) between the
blastostyle and the perisare of the gonotheca. 2. The gonophore
develops entocodon, manubrium, and radial canals, but is devoid
of velum and tentacles (? Laomedea repens). 3. The gonophore
develops no entocodon; the ectoderm is multilaminate ; traces of
an endoderm lamella are indicated (female Sertularia pumila), or
are entirely absent (Aglaophenia). 4. No trace of the gonophore
remains ; the generative cells are borne directly on the blastostyle
(male Sertularella polyzonias).

In these simplified gonophores the generative cells frequently
lie in the manubrium, as in the Anthomedusae, but not in the
position of the radial canals, as is the case with the free-swimming
medusoids of this group. The gonophore or the blastostyle may
grow directly from the hydrocaulus (Campanulina); most com-
monly they arise from the axil between a hydrotheca and the
hydrocaulus or hydrocladium (Halecium), or in the centre of a
hydrocladium (Aglaophenia). They may spring directly from the
hydrorhiza (Coppinia).

THE GONOTHECA AND PHYLACTOCARP.—In most cases the
gonophore, or the blastostyle and gonophore, are enclosed in a
rigid, horny capsule, continuous with the perisare, and termed the
gonotheca (Fig. 35). This is generally oval, or shaped like a flask or
an amphora ; and is either smooth (Obelia), spinose (Plumularia), or
annulated (Campanularia). It encloses either a medusoid (Cam-
panulina), or a blastostyle carrying medusoids (Obelia), or a
sporosac (male Halecium), or a blastostyle carrying sporosacs
(male Plumularia). It is frequently provided with a hinged oper-
eulum (Plumularia).

The modifications connected with the gonophore and gonotheca
vary greatly in different genera and species, and even in different
sexes of the same species ; only a few of their types can be sketched
here.

1. In Gonothyraea, as already mentioned, a hardly disguised
medusoid is developed; each gonophore, when nearly mature,
migrates up the blastostyle and projects beyond the mouth of the

28 THE HYDROMEDUSAE

gonotheca, seated upon a peduncle continuous with the opercular
plate. This type of gonophore has been termed a meconidium.

2. In Calycella lacerata a blastostyle and gonophore at first lie
inside a gonotheca of the usual type; the gonophore when nearly
mature migrates up the blastostyle, and projecting beyond the
mouth of the gonotheca, secretes a spherical gelatinous cyst, the
acrocyst, in which it completes the maturation of the generative
cells. In Sertularia pumila the gonophore, having formed the
acrocyst as above described, withdraws again into the gonangium,
leaving the ova behind to develop (Fig. 36).

Fia, 85, Fia, 86, Fria. 87.

85.—Gonotheca of Obelia, From the central blastostyle are budded numerous gonophores,
each of which becomes a free-swimming medusoid. (After Allman.)

86,—Diagrammatic section of the gonophore of Sertularia pumila, A, the acrocyst, con-
taining ova; B, coelenteron of the blastostyle; G1, the first gonophore (sporosac), Which has
formed, and retired from, the acrocyst, connected with the perisare on the left by strands of
tissue (gubernacula); G2, the second gonophore at an early stage of formation on the blasto-
style; OP, opercular plate, an expansion at the distal end of the first gonophore ; /, perisare of
the gonotheca, (After Weismann.)

87.—Phylactocarp (corbula) of Aglaophenta attenuata, side view. At the point of origin of
the phylactocarp from the hydrocladium is a hydrotheca with the usual three nematophores ;
the phylactocarp itself is composed of ribs carrying numerous nematophores ; the ribs figured

arch over to meet those of the other side, and cover the gonophores (not shown in the figure).
(After Allman.)

3. In Sertularia rosacea, in which the gonophore is also
borne on a blastostyle, the opercular plate sends out eight hollow
arms, consisting of the usual body layers; these, projecting out-
wards beyond the mouth of the gonotheca, secrete eight flat spines.
which bend inwards to serve as a marsupium for the reception and —
protection of the acrocyst.

4, Another method of protection for the gonophore is found

4

THE HYDROMEDUSAE 29

in the family Plumularidae, where the modification of a hydro-
cladium results in the formation of a special organ termed the
phylactocarp, the complexity and completeness of which vary greatly
in different genera and species. (a) All the hydroids of a hydro-
cladium may be suppressed and replaced by gonophores (or blasto-
styles), which are guarded by the usual median and lateral nemato-
phores (Lytocarpus). (+) The hydroids, instead of being sessile in
the centre of the axis of the hydrocladium, project laterally out-
wards, their central position being occupied by the gonophores ; the
peduncles on which the hydroids project are produced each into
a long rib (homologous, according to Allman, with an elongated
median nematophore), which bears numerous lateral nematophores.
These ribs arch slightly over the gonophores (Acanthocladium),
(c) All the hydroids of the hydrocladium, except one or two nearest to
the hydrocaulus, are suppressed ; the ribs of nematophores, formed
as described under ()), arch completely over the gonophores, forming
what is termed an open corbula (Aglaophenia attenuata, Fig. 37).
(d) In a further stage, deducible from the last, the ribs join to
form a complete investment of the gonophores, except for one
(Aglaophenia filicula) or several (A. Macgillivrayi) apertures. In
this manner the simple hydrocladium becomes converted into a
closed corbula.

ORIGIN OF THE GENERATIVE CELLS.—The general description
of the origin and migration of the generative cells in Anthomedusae
applies also to this group, but the changes there mentioned as
affecting the structure and functions of the gonophore, and the
acceleration of the formation of the generative cells, are even more
marked in the Leptomedusae. In most cases the cells, although in
all probability migrants from the ectoderm, are first noticeable in
the endoderm; only rarely are they confined throughout to the
ectoderm (male Campanularia). They may make their first
appearance on the manubrium and migrate on to the radial canals
of the medusoid, in which case they are probably always ecto-
dermal] in position (Obelia); or they may appear in the endoderm
of the blastostyle (male Campanularia), of the hydrocaulus
(Gonothyraea), or of its lesser branches (female Campanularia).
When a free-swimming medusoid is not present, they migrate
from their place of formation into the gonophore, and generally
penetrate through the mesogloea into the ectoderm of the rudi-

mentary manubrium or of the sporosac, as in the Anthomedusae ;

_e

they rarely ripen in the endoderm (Sertularella). For the whole
question see Weismann (10).

ASEXUAL REPRODUCTION.—Gemmation is of the same laminar
character in hydroids of the Leptomedusae as in those of the
Anthomedusae. In the gemmation of gonophores from a blasto-
style, it frequently happens that the ectoderm is multilaminar ;

”
Ae o

30 THE HYDROMEDUSAE

the entocodon and exumbral ectoderm of the gonophore are —
then developed from the inner layer, the outer layers remaining as
cups or strands of blastostylar ectoderm (Fig. 36) between the
gonophore and the perisare of the gonotheca (gubernaculum).
Gemmation from a medusoid has rarely been noted (Thaumantias
—Sars, 36),

Fission in hydroids has occasionally been observed under a
curious form ; a small piece of coenosare at the end of a growing
branch becomes nipped off from the colony, and gives origin to a
hydrorhiza, from which a new colony is produced by gemmation
(Schizocladium—Allman, 1). In medusoids fission is very rare
(Eucope—Lang, 34; Brooks, 35).

SEXUAL REPRODUCTION.—The male and female cells are as a
rule borne upon separate colonies, but both may occur in different
gonophores on the same colony (Diphasia fallax). Both have even
been recognised in the same gonophore, but in this case the male
cells alone come to maturity (Gonothyraea). One or more ova may
be present in each gonophore; when the potential ova are
numerous, one, or one at a time, generally matures at the expense
of the rest.

The general outline of development indicated above as occurring
in the Anthomedusae holds good also for this group.

ORDER 3. Trachomedusae.

DEFINITION.—Hydromedusae in which the medusoid develops
directly from the ovum (hypogenesis) ; no alternation of hydroid
and medusoid generation occurs. The chief sense organs are ten-
taculocysts, with endodermal otoliths, generally enclosed in vesicles.
The generative organs lie on the radial canals.

The bell of the MEDUSOID in this group (Figs. 38, 39) is generally
hemispherical, with a thick mesogloea (Geryonia), but is sometimes
thin, and conical or prismatic (Aglantha) ; it is always of firm con-
sistence and is provided with a strong velum. The edge of the bell
is provided with a special ring of cnidoblasts, with the usual nerve
ring, and in some cases with spiral marginal cirrhi, but the marginal
tubercles and funnels of the Leptomedusae are not represented.
Suckers are rarely developed on the edge of the bell (Pectanthis).

The primary or perradial fentacles are solid, with a cartilaginous
endodermal axis ; between them are often developed interradially
secondary tentacles, which are also solid; both primary and
secondary tentacles may be either lost or retained, and replaced or
supplemented by tertiary hollow tentacles. The tentacles are
tipped by a sucker in a few genera (Pectanthis).

In a few cases the perradial tentacles are alone developed,
either four (Liriope) or six (Geryonia) in number. To these may

THE HYDROMEDUSAE 31

be added either four (Sminthonema) or six (Geryones) interradial
tentacles. By further additions they may amount to more than a
hundred (Olindias); in Pectanthis they form sixteen bundles.
The tentacles are
often arranged in
two or more rows
in such a manner
that some take
origin, not from
the extreme mar-
gin of the bell, but
at a little distance

from it on the
exumbral surface ;
the endodermal

axis of the ten-
tacle still retains
connection with
the more central
endoderm, by
bending inwards
through the thick
exumbral meso-
gloea. This bent
axis, together with
bands of enido-

Y vee
a) tak
oO
\ ae at } =

blasts, which run
from the marginal
ring already men-
tioned to the point
of attachment of
the tentacle, give
rise to the char-

Fic. 38.

Carmarina (Geryonia) hastata (after Haeckel). a, nerve [and
cnidoblast ring; a’, radial nerve and canal; 0b, tentaculocyst;
c, circular canal ; ¢, blind centripetal canal ; g”, ovary ; h, peronium
or cartilaginous process ascending from the cartilaginous margin
of the dise centripetally in the outer surface of the jelly-like disc ;
six of these are perradial, six interradial, corresponding to the
twelve solid larval tentacles, resembling those of Cunina; k,
dilatation (stomach) of the pseudo-manubrium; 1, jelly of the
dise ; p, pseudo-manubrium ; t, tentacle (hollow and tertiary, i.e.

preceded by six perradial and six interradial solid larval tentacles) ;
u, cartilaginous margin of the dise covered by thread cells; v,
velum. (From Lankester.)

acteristic mantle
rivets or peronia.

The musculature of the bell is of the usual type, except for the
great development of radial muscle bands along the course of the
radial canals through the subumbrella and pseudo-manubrium.

In two out of the four families into which this group is
divided (Petasidae, Trachynemidae) the general relations of parts
of the medusoid are of the type already familiar (Fig. 5); but
in the other two (Aglauridae, Geryonidae) the gastric cavity does
not lie in the subumbrella, but is situated at the distal end of the
apparent “manubrium” ; the latter is really a prolongation of the
subumbrella, solid except for the radial canals, and may be termed
a pseudo-manubrium. The mouth is generally surrounded by four

32 THE HYDROMEDUSAE

(Aglantha) or six (Geryonia) short perradial lappets; in the
Petasidae and Trachynemidae it opens through the short manu-
brial cavity into the subumbral gastric cavity ; in the Aglauridae
and Geryonidae it opens directly into the gastric cavity of the
pseudo-manubrium. The perradial canals which lead from the
gastric cavity are four
(Liriope) or six (Gery-
onia); to these inter-
radial canals are often
added; both open as
usual into a_ circular
canal.« From the latter,
in old specimens of many
species, blind centripetal
canals grow backwards
towards the apex of the
bell, but never reach the
gastriccavity (Geryonia);
their number varies, but
may amount to twenty-
Z seven between every two
A radial canals (Olindias).
Fic. 39, The generative cells are
Diagrammatic vertical section of Carmarina hastata, formed on the underside
perradial canal, and fon the left through the outspread Of the radial canals, either
lobe of an ovary, a lateral extension of a similar canal. jy their course through

1, mesogloea of the disc and pseudo-manubrium ; 7, per-

radial canal; rs, its outer, vi, its inner wall; g, gener- the subumbrella (Gery-
ative cells; k, gastric cavity; Z, tongue-like process; h, ;
peronium ; ¢, circular canal; uk, mens ied marginal onia) or through the

ring. (From Lankester, after Gegenbaur. pseudo -manubrium
(Aglaura). The cells are arranged in bands, which are flat and
do not project on the subumbral surface (Geryonia), or in sacs
which depend into the bell cavity from the subumbrella (Aglantha),
or from the pseudo-manubrium (Aglaura). In the Pectyllidae the
sacs are perradial and interradial in position, and are each divided
into two, and supported by a lamina which passes across the bell
cavity from the manubrium to the radial canals (mesogonia) ; these
laminae do not appear to have any relation to the mesenteries of
Scyphomedusae. The sense organs are ocelli and tentaculocysts.
Ocelli ave comparatively rare in this group; when present they are
generally simple pigment specks, and only occasionally possess a
lens (Olindias ?). The tentaculocysts are primarily superficial, four
in number, and perradial in position (Petasus). By their displace-
ment and by the intercalation of others there come to be, in
many cases, eight (Marmanema) or twelve (Geryonia) nearly per-
radial and interradial tentaculocysts, or sixteen adradial (Rhopa-
lonema). In Olindias there are between one and two hundred of

eae ML

THE HYDROMEDUSAE 33

these organs. By.a secondary growth they become, in many
cases, enclosed by an overgrowth of ectoderm, so that they lie in
sacs, which either project on the surface (Trachynema) or are
sunk in the mesogloea (Geryonia).

SexvuaL Repropuction.—(No form of asexual reproduction
is known among Trachomedusae.) The sexes are separate, the pro-
duct of the fertilised ovum is always a medusoid. Segmentation
of the ovum is complete ; the endoderm is formed by delamination
from the ectoderm. The secretion of mesogloea between ectoderm
and endoderm is considerable, except at one pole of the spherical
larva, the pole where the mouth is pierced and the tentacles are
formed. At this stage the organism presents some resemblance to
a hydroid larva, but its conversion to the adult form is achieved
by continuous metamorphosis, consisting chiefly in a flattening of
its spherical outline and an assumption of the characteristic bell-
shape of the adult. The originally simple coelenteron is converted
into the canal system of the adult by fusion of the endoderm,
except along certain lines, forming an endoderm lamella of the
usual type.

ORDER 4. Narcomedusae.

DEFINITION.—Hydromedusae in which the medusoid form (with
one exception) develops directly from the ovum (hypogenesis) ;
no alternation of hydroid and medusoid generation occurs. The
chief sense organs are tentaculocysts with endodermal otoliths,
never enclosed in vesicles. . The generative organs lie on the
subumbral floor of the gastric cavity or gastric pouches.

The bell of the meDUSoID (Figs. 40, 41) is generally flattened,
and provided with a strong velum,; the mesogloea is thick and
extremely tough. The bell is furrowed and its edge incised into
a series of lappets, by the peronia, which, as in the Trachomedusae,
radiate from the exumbral origins of the tentacles outwards to
the circumference, marked by a stripe of cnidoblasts from the
marginal ring. The edge of the bell being thus incised, the
marginal nerve ring and ring of cnidoblasts are festooned to a greater
or less extent round the lappets, instead of forming the unbroken
circle which is generally characteristic of the groups already
described.

The four primary tentacles are always placed perradially ; they
are retained throughout life (Cunantha), or two of them are
dropped (Aeginella), or four interradial tentacles are added
(Aegineta) ; many forms however develop more (Solmaris). They

_ are always solid, and are placed in most cases on the exumbrella
at some distance from the margin, their endodermal axis penetrat-
ing far into the mesogloea; they retain, however, an endodermal
connection with the circular or festoon canal or with the gastric

3

34 THE HYDROMEDUSAE

cavity, and an ectodermal connection of cnidoblasts and sense
cells with the two marginal rings, thus forming the characteristic
peronia. The sense organs are always free ftentaculocysts at the
margin of the bell ; they are never closed as in the Trachomedusae ;
originally they are always four in number and interradial in
position ; this number may be retained throughout life (Cunantha),
but by later additions they may become extremely numerous
(Cunina). The otoliths are secreted by one or more endoderm
cells in each tentaculocyst; they are generally crystalline,
occasionally spherical. Stripes of ecnidoblasts, like that of the
peronium, which run from their bases up on to the exumbrella,
form the characteristic otoporpae. The cavity of the subumbrella is
small, when compared with that of previously described groups,

Fia. 40. Fic. 41.

40.—Aeginura myosura, a species with eight tentacles and sixteen tentaculocysts; letters
as in Fig. 41. (After Haeckel.)

41.—Half-section of Cunina. CC, circular canal; G, gonad; L, dotted outline of lappet;
between each pair of lappets lies a peronium and a tentacle; WM, mouth; NR, nerve ring ; Pe,
peronial canal; Re, radial canal; 7, tentacle, the root of which penetrates to the radial canal ;
V, velum. (After Haeckel.)

owing to the great development of the gastric cavity ; and its
musculature is far weaker.

The COELENTERON in most members of this group differs some-
what from the type already familiar. The manubrium is generally
absent, the mouth opening directly into the gastric cavity ; it is,
however, sometimes present, though short (Cunina). The gastric
cavity is large, and occupies almost the whole of the subumbral
aspect. In the Cunanthidae, the radial canals are short, broad, and
shallow pouches, extending as far only as the base of each tentacle ;
at this point each canal is split by the peronium into two peronial
canals which, after a short radial course, turn round the edge of the
bell in festoons to form the circular or festoon canal. In the Pegan-
thidae and Aeginidae the conditions are much the same as in the
Cunanthidae, but the radial canals are practically suppressed ; the
peronial and festoon canals remain. In most members of the Sol-

THE HYDROMEDUSAE 35

maridae, the radial, peronial, and festoon canals are suppressed,
being represented only by solid cords of endoderm cells.

The arrangement of the generative organs varies considerably ;
they are always developed from the subumbral wall of the
coelenteron, but may form either a continuous ring (Solmaris), or
radial pouches (Cunina) ; the radii in which they lie are specifically,
not generically, characteristic.

REPRODUCTION.—In some cases the development of the medu-
soid from the fertilised ovum follows along the lines of a continuous
metamorphosis, the diblastula becoming gradually converted into
the form of the adult medusa (Aeginopsis mediterranea). In
Cunoctantha octonaria the diblastula becomes parasitic on an
Anthomedusan (Turritopsis) ; and both it, and buds formed from it,
gradually assume the adult form by a continuous metamorphosis.
The life-histories of some other forms cannot be said to be as yet
fully understood ; in Cunina parasitica the diblastula is parasitic on
Geryonia hastata ; its buds become Narcomedusae of a somewhat
Solmaridan type, but the planula does not itself develop into a
medusa ; there is thus here an apparent alternation of at least
two different generations. In Cunina proboscidea a form of asexual
reproduction termed sporogony has been described; neutral
amoeboid cells, neither ova nor spermatozoa, wander from the
generative organs into the endoderm and mesogloea, and develop
into medusae (Metschnikoff, 13; Brooks, 14; Maas, 44).

ORDER 5. Hydrocorallinae.

DEFINITION.—Colonial metagenetic Hydromedusae with a cal-
careous skeleton, into which the gastrozooids and dactylozooids can
be retracted. The skeleton is perforated by coenosarcal tubes, on
which the gonophores are generally formed.

The Hydrocorallinae (Moseley, 37) are colonial and trimorphic
and secrete without exception a massive (Millepora) or branching
(Allopora) calcareous skeleton, the coenenchyme (coenosteum). The
relations of this skeleton are best understood by the conception of a
branching and anastomosing hydrorhiza, the ectoderm of which
secretes, not a horny perisarc, but calcareous trabeculae which fill all
the interspaces between the tubes of soft tissue. The surface of the
coenenchyme is either pitted with pores of two or more kinds,
gastropores and dactylopores, into which the gastrozooids and
dactylozooids can be withdrawn (Millepora, Fig. 42), or is produced
into spouts (Spinipora) or cups (Stylaster) for the same purpose.
The pores may be scattered, or may be arranged in definite systems,
in which the dactylozooids are in lines parallel to, and on each
side of, a line of gastrozooids (Distichopora), or in circles round
the gastrozooids (Stylaster), Fig. 43, band c. A circular system

36 THE HYDROMEDUSAE

(cyclosystem) may be protected by a calcareous flange (Cryptohelia) ;
in some cases calcareous laminae between the dactylozooids of a
cyclosystem simulate the arrangement of septa in an Anthozoan
theca (Allopora). In branching forms the whole thickness of the
branch is often permeated by coenosarcal tubes ; in massive forms
the living tissues are confined to the circumference, and by secreting
plates of coenenchyme behind them as they grow peripherally
outwards, give rise to fabulae below the zooids. Calcareous brush-
like styles rise in some instances from the tabplae of both gastro-
pores and dactylopores (Stylaster), or in the gastropores only

42,—Portion of the caleareous corallum of Millepora nodosa, showing the cyclical arrange-
ment of the pores occupied by the hydroids. Twice the natural size. (From Moseley.)

43.—Enlarged view of the surface of a living Millepora, showing five dactylozooids surround-
ing a central gastrozooid, (From Moseley.)

(Distichopora). Special pits for the reception of the gonophores
may occur in the coenenchyme, and are termed ampuilae.

The coenosare is covered by a superficial sheet of ectoderm
which is provided with very large nematocysts. This sheet, which
is perhaps composed of two layers, rests partly on spines of the
skeleton, partly on the blind ends of the coenosarcal tubes, and in
retraction is continued downwards as a lining to the pores; here
it becomes continuous with the ectoderm of the zooids, and appears
to form a circular operculum over them when retracted completely.
Elsewhere than in this sheet, ectoderm, mesogloea, and endoderm
bear to one another the relations usual in Hydrozoa.

The hydroids (Fig. 43) are of two kinds. The gastrozooids, the

THE HYDROMEDUSAE 37

nutritive zooids of the colony, may possess capitate tentacles
(Millepora), generally four, six, or twelve in number, or may
be entirely devoid of tentacles (Astylus). The endoderm cells
near their mouths are swollen and secretory. The dactylozooids
are generally devoid of mouths, and either have (Millepora) or
lack (Stylaster) capitate tentacles; their endoderm cells are not
enlarged. In some genera two kinds of dactylozooids are dis-
tinguishable by size and position (Spinipora).

Both forms of hydroid have strong retractor muscles, and

Fic. 43a.

Skeletons of Allopora (upper left hand), Errina (lower left hand), and
Stylaster (right hand),

large complex nematocysts ; they are composed of the usual body
layers, and are connected at their bases with the tubular coenosarc
by radiating tubes.

The structure of the gonophores (Hickson, 38) varies considerably
in different genera, but is apparently in all cases referable to a
simplification of the medusoid type, such as has been sketched in
Anthomedusae (p. 20). The gonophore is not known to be ever
freed; it develops neither velum, tentacles, mouth, nor sense organs ;
a manubrium is not invariably present. In Millepora Murrayi the
gonophore is formed at the apex of a dactylozooid (cf. Limnocodium,
Scyphistoma), in the other forms hitherto investigated it is formed

™

38 THE HYDROMEDUSAE

on the course of the coenosarcal canals, and often lies in a special
pit of the coenenchyme, termed the ampulla. An entocodon is not
formed in the usual way ; instead of this, which is an ectodermal
downgrowth to be hollowed out eventually into the subumbral
cavity, the body wall at the sides of the generative cells grows
upwards, and arches over the manubrium to form the same cavity
(Millepora). All traces of medusoid structure are lost in some
cases (male Distichopora). Radial canals may be entirely absent

uw

Fic. 43d.

Fic. 48e.

48b.—Diagrams illustrating the successive stages in the development of the cyclosystems

Stylasteridae. 1, Sporadopera ; 2, $, ANopera ; 4, 5, Stylaster; 6, Astylus subviridis; T,

Distichopera coccinea, s, style ; dp, dactylopore ; gp, gastropore ; }, in fig. 6, inner horseshoe-
shaped mouth of gastropore. (After Moseley, from Lankester.)

43c.—Portion of the corallum of Astylus subviridis (one of the Stylasteridae), showing
cyclosystems placed at intervals on the branches, each with a central gastropore and zone of
slit-like dactylopores. (After Moseley, from Lankester.)

(Millepora), or may be present in varying numbers (twelve in
female Distichopora).

REPRODUCTION.—Asexual gemmation of hydroids is apparently
of the usual laminar character. The development of the sexually-
produced embryo has not been traced.

OrpDER 6. Siphonophora.

DEFINITION.—Colonial free-swimming Hydromedusae with
numerous polymorphic modifications of both hydroid and

THE HYDROMEDUSAE 39

medusoid, and a metagenetic life-history.
freed, generally sessile.

The Siphonophora (for the literature of which Haeckel, 39 ;
Chun, 40, 41 ; and Schneider, 42; should be consulted) are invari-
ably free-swimming, colonial, and polymorphic. Just as the planula
in some Anthomedusae does not
itself develop into a hydroid,
but becomes a budding hydro-
rhiza, so in all probability, in
this group (a part at least of),
the planula is to be regarded
as itself giving origin to the
coenosarc, and as _ budding
numerous individuals of vary-
ing form and function. The
composition of the colony is
very different in the different
families, but is generally a
combination of some of the fol-
lowing hydroid or medusoid
individuals.

PoLtymMorPHIC MODIFICA-
TIONS OF THE HyDROID :—

1. The gastrozooid (siphon,
polypite) has a large mouth,
and is provided with nemato-
cysts; at or near its base is
usually placed a single tentacle
(Figs. 44,¢,; 51,@). The tentacle

Gonophores_ rarely

is generally extremely long and
contractile ; it is tubular, and is
either itself provided with bat-
teriesof nematocysts(Apolemia),
or bears a large number of fine
lateral threads or tentilla, carry-
ing numerous nematocysts
(Forskaélea). The latter can

Fia. 44.

44.—Diagram showing possible modifica-
tions of medusoids and hydroids of a colony
of Siphonophora. n, pneumatophore ; k, necto-
phores (swimming bells); J, hydrophyllium
(covering piece); i, generative medusoid; g,
dactylozooid with attached tentacle, h; e, gas-
trozooid, with branched grappling tentacle,
f; m, stem or corm. The thick black line
represents endoderm, the thinner line ectoderm,
(After Allman.)

sometimes be spirally retracted into a protective cup or involucrum
(Agalmopsis). In some cases no tentacle is developed (Velella).
The endoderm of the gastrozooid is generally pigmented, and often
projects as villi into the coelenteron.

2. The dactylozovid (hydrocyst, palpon) is generally devoid of
a mouth, and provided liberally with nematocysts. The palpacle
or tentacle of the dactylozooid is never branched, and generally
grows on or near the base (Figs. 44, 9,; 51, D, 7’). No tentacle is
developed in some cases (Velella), To such an extent are the

40 THE HYDROMEDUSAE F

modifications of polymorphism carried in this group, that it is
sometimes impossible to form an opinion as to whether a particular
structure is to be regarded as tentacle or dactylozooid.

3. The blastostyle (gonostyle, sexual palpon or siphon) which
produces sexual medusoids by gemmation, is generally devoid of
a mouth, but not invariably (Velella—Fig. 48, BL). It develops
no tentacles. The blastostyle sometimes branches into a gonodendron
(Physalia), (Fig. 51).

POLYMORPHIC MODIFICATIONS OF THE MEDUSOID :—

4. The sexual medusoid is set free from the colony (? Physalia,
Velella) or remains fixed (¢Physalia). It may have the typical
structure of the Anthomedusan medusoid (Velella), or may exhibit
the various stages of arrest in development already described (p.
20). Even when arrested at an early stage it is sometimes freed,
and swims by means of cilia (¢ Forskailea); more often it is a
permanently fixed sporosac (d Physalia). The medusoid is budded
from a blastostyle (Velella, Fig. 48), from the ccenosare (Agalmopsis),
or from the pedicle of the gastrozooid (Diphyes, Fig. 47). Most
colonies of Siphonophora are hermaphrodite, and in some cases
so also are the gonodendra (Physalia) ; the medusoids are either
male or female.

5. The nectophore (nectocalyx, nectozooid) is a medusoid
devoid of tentacles, manubrium, and mouth, but retaining the
characteristic velum, circular, and radial canals (Figs. 44, &; 45,
m; 46, WN’). The musculature is well developed. The necto-
phore has a locomotor function.

6. The hydrophyllium (bract, phyllozooid) is a shield-shaped
medusoid, of protective function (Figs. 44,1; 47, H). It consists
typically of a somewhat curved plate of thick mesogloea, covered
externally by ectoderm, and containing a solid endodermal core
(phyllocyst). Its medusoid origin may be inferred from a few
species in which it retains a structure intermediate between that of
medusoid and typical hydrophyllium ; in Athoria, for example,
its apex is excavated into a rudimentary subumbral cavity with
minute circular and radial canals, and four knobs representing
rudimentary tentacles.

7. The pnewmatophore, an apical air sac of hydrostatic function,
appears under two quite distinct forms.

(a) Inthe Physonectae and Cystonectae, it is probably a highly
specialised medusoid, the exact homologies of which are obscure
(Figs. 44,2; 45, a’; 49, PN). It is formed typically as a swelling
at the upper end of the coenosare, into which in the course of
development an entocodon pushes its way. The ectodermal
cavity thus produced is distinguishable into two regions—a
central part, the air gland, secretes a gas which passes through
a pylorus into a distal part, the air sac, lined by a chitinous

_ #

THE HYDROMEDUSAE 41

Fia. 47.

45.—Physophora hydrostatica. a, stem or corm of the colony; a’, pneumatophore (air-

bladder) ; m, nectophore ; 0, orifice formed by the margin of the umbrella ; f, hydrophyliia; n

gastrozooid ; i, tentacles ; g, sporosacs, (From Gegenbaur.) i at

46.—Diagram of the structure of a Diphyid. C, coenosare carrying cormidia ; CC, cir-

- cular canal of nectophore ; H, hydroecium; N’, upper, and N”, lower, nectophore ; P, pedicle

oe as) nectophore; RC, radial canals of nectophore; SO, somatocyst. (Modified from

aeckel.

47.—Diagram of the structure of an Ersaeome (free monogastrie generation of a Diphyid).

G, gastrozooid; H, hydrophyllium; M, sexual medusoids; N, nectophore; OL, oleocyst ;
7, tentacle of gastrozooid. (Modified from Haeckel.)

17

42 THE HYDROMEDUSAE

secretion. Between the air gland and the outer wall of the
pneumatophore lie in many cases radial pouches and septa of
varying number, which perhaps correspond to the radial canals
of a medusoid. The air sac may be closed (most Physonectae)
or open by a pore to the exterior (most Cystonectae),

(b) In the Disconectae the pneumatophore is at first a single
chitinous chamber ; round this are addéd concentrically and in
one plane chitinous tubes of varying number, which communicate
with each other, and with the central chamber, by pores in their
walls, and in some places open also to the exterior. The chitinous
plate thus composed may bear a crest or sail, set at right angles to
the plane of the plate, but obliquely to its longer axis (Velella),
and is covered on all sides by the ectoderm which secretes it. Air
tubes or tracheae from the pneumatophore penetrate the centradenia.
There is reason for supposing that the pneumatophore even in the
Disconectae is derived from a highly modified medusoid (Figs. 48,
PN; 50).

8. The aurophore is perhaps also a highly modified medusoid, char-
acteristic of the Auronectae ; it is placed at the side of the pneumato-
phore, is ovoid in shape, and is traversed by a minute canal which
leads from the cavity of the pneumatophore to the exterior. Round
this canal lies the pistillum, a mass of muscle enveloped ina strong
chitinous tube ; external to this lie successively ectoderm, meso-
gloea perforated by branching endodermal tubes, and the super-
ficial ectoderm (Figs. 48), 48c). The function and homologies of
the aurophore are most obscure (Fewkes, 43).

TYPES OF SIPHONOPHORE COLONIES :—

The polymorphic individuals above described are very differ-
ently combined in the different sub-orders of the Siphonophora.

(a) In the Disconectae (Fig. 48) a single gastrozooid is sur-
rounded by numerous blastostyles, and, beyond these, by numerous
dactylozooids. They all spring from a mass of coenosare which
underlies the pneumatophore, composed of ectoderm, mesogloea, and
ramifying endodermal tubes; the cells of the latter are apparently in
some places renal, in others hepatic, in function ; the whole strue-
ture is termed the centradenia, and is perforated by tracheae. The
coenosare entirely envelops the pneumatophore, and projects
laterally for some distance beyond it; at its edge runs a cir-
cular canal,

(b) In the Calyconectae (Figs. 46, 47) no pneumatophore is
developed. There are one or two, rarely more, large nectophores, the
uppermost of which has on one side either an open groove (Cym-
bonectes) ora tube closed at the upper end (Diphyes)—the hydroectum
or infundibulum, lined by ectoderm. From the upper end of this
cavity spring both the pedicle of the second nectophore when present,
and the long tubular coenosare (Diphyes, Fig. 46) ; or the nectophores

-

THE HYDROMEDUSAE 43

Fic. 48a.

Fia, 48,

48.—Diagram of the structure of Velella, showing the central and peripheral thirds of
a half-section of the colony, the middle third being omitted. ‘Ihe ectoderm is indicated by
close hatching, the endoderm by light hatching, the mesogloea by thick black lines, the horny
- skeleton of the pneumatophore and sail by dotting. BL, blastostyle ; C, centradenia ; D, dacty-
lozooid ; EC, edge of colony, prolonged beyond the pneumatophore ; G, cavity of the large
“central gastrozooid ; M, medusoids attached to blastostyles ; PN, primary central chamber, and
PN’, a concentric chamber of the pneumatophore, the former showing the opening into the
second chamber, the latter showing an opening to the exterior, and a “‘ trachea”; S, sail.
48a.—Porpita from the aboral aspect, showing the pneumatophore, and expanded dactylo-
zooids. (After Agassiz.)

Fig. 48b.—Stephalia corona, a young colony. (After Haeckel.)

Fia. 48c¢,—Stephalia corona, colony in section, (After Haeckel.) ao, mouth of the primary
gastrozooid, the cavity of which is continuous with the axial canal (ca) and the canal plexus
(ac) of the colony. The large pneumatophore (p) is surrounded by a ring of nectophores (7),
from among which projects the large aurophore (/). The opening of the aurophore (lo) leads
through the pistillum (/m) into the cavity of the pneumatophore ; (s), secondary gastrozooids
with (¢) tentacles.

THE HYDROMEDUSAE 45

are attached side by side, leaving an incomplete hydroecium between
them (Praya); or the hydroecium is altogether absent (Galeolaria),
It serves essentially as a protective canal, into which the coenosare
may be withdrawn. The coenosarc is extremely long, tubular, and
contractile ; its endoderm is continued upwards beyond the hydroe-
cium as the blind somatocyst (acrocyst), the upper end of which
usually secretes an oil globule, presumably of hydrostatic function
(oleocyst). The coenosare carries either a cormidiwm, or numerous
cormidia at regular intervals separated by free internodes; they
are aggregations of individuals, which may in some cases become
freed from the colony. They generally appear under one or other
of two main forms—Eudoxomes, which consist typically of hydro-
phyllium, gastrozooid with tentacle, and one or more medusoid gono-
phores ; or Ersaeomes, in which typically a nectophore is added to
the persons which occur in the Eudoxome. In some cases hydro-
phyllia are absent ; in others more than one gastrozooid is present
in each cormidium (Apolemia).

(c) In the Physonectae (Fig. 45) the coenosarc is generally long
and tubular, and carries at its apex a small pneumatophore ; below
this generally occur series of nectophores followed by series of
hydrophyllia ; but either may be developed without the other ;
these are followed by the cormidia. There may be only a single
gastrozooid (Athoria); generally they are numerous. Dactylo-
zooids are generally present, each provided with a simple palpacle ;
sometimes they have an oral opening, and appear to serve for excre-
tion (cystons). The cormidia are generally ordinate, with free
internodes, but are rarely scattered irregularly along the stem
(Forskalea). Each cormidium is composed typically of a gastro-
zooid with a branched tentacle, one or more hydrophyllia, blasto-
styles, gonophores, and cystons.

(d) In the Auronectae (Figs. 48a, 48)) a small and highly
modified sub-order, the coenosare is short and very thick, and is
traversed by anastomosing canals. It is covered above by a large
pneumatophore, provided “dorsally” with an aurophore; below
this lies a corona of nectophores. The lower part of the coenosare
is covered by cormidia more or less ordinate in arrangement, each
consisting primarily of a gastrozooid with tentacle, a branched
gonodendron, and a palpon (dactylozooid).

(e) In the Cystonectae (Fig. 49) a large pneumatophore is also
developed, but the family is distinguished by the complete absence of
nectophores and hydrophyllia. The coenosare is long and tubular
(Rhizophysa), or short and wide (Physalia); in the former case
the cormidia are generally ordinate, in the latter they are arranged
in a multiple series along the ventral side of the trunk ; they con-
sist typically of one or more tentaculate gastrozooids, of gono-
dendra, and dactylozooids. :

~

46 THE HYDROMEDUSAE

ReEPRODUCTION.—The asexual reproduction of this group is
apparently of the usual laminar type: medusoids, nectophores,

~

Fig. 49.
PN

Fie. 51,

49.—Diagram of Physalia (modified from Cuvier and Haeckel),

50.—Upper surface of Velella, showing pneumatophore and sail (after Cuvier),
51.—Cormidium of Physalia, with a gonodendron (modified from Haeckel).

D, dactylozooid ; G, gastrozooid; GP, gonopalpon or dactylozooid on the gonodendron ;

M9, female medusoid, ultimately freed ; Mg, male sporosac ; PN, pneumatophore ; 7, tentacle
(palpacle) of dactylozooid or palpon,

and (sometimes) hydrophyllia are formed after the manner sketched
on p. 20. The development of the fertilised ovum is known only

THE HYDROMEDUSAE 47

from observations on a few forms which are too widely different to
allow of a general developmental scheme being as yet laid down.
A planula is apparently always formed ; the first individual budded
from it may be a pneumatophore (Halistemma), nectocalyx
(Epibulia), or hydrophylliam (Agalma). The coenosare may be
a lateral extension of the first gastrozooid (Cystonectae), or may
he its elongated stem (? Physophoridae, Calyconectae).

APPENDIX TO HypROMEDUSAE. No, I.

Limnocodium and Limnoenida.

These are two freshwater medusae, the first-named known only from
the Victoria Regia Tank of the Royal Botanic Society in London, the

52.—Limnocodium, as seen floating, x 5. MR, marginal nerve and cnidoblast ring; Ve,
velum ; P7', perradial tentacle. (After Lankester.)

53.—Polyps of Limnocodium on weed (after A. G. Bourne).

54.—Diagram of the sense organs of Limnocodium and,Limnoenida. C, cavity of the
vesicle, which in Limnocodium is continued as a canal into the velum; ZC, ectoderm of the
sense organ; HC", ectodermal lining of the vesicle; EN, refringent endoderm cells of the sense
organ ; LN’, granular endoderm cells of the sense organ ; LN”, position of endoderm of the cir-
cular canal. (After Lankester and Giinther.)

second known only from Lake Tanganyika. They undoubtedly belong to
the Hydromedusae, and to different orders of the class, but it is still a
matter of difficulty to assign them to any of the existing orders.
Limnocnida (Fig. 55) presents points of resemblance both to Antho-
medusae and to Narcomedusae. It shares the manubrial position of its
generative organs with both these orders; but in the shortness of the

48 THE HYDROMEDUSAE

Fic. 55.—Limnocnida from the oral surface (after Giinther).

manubrium and shallowness of the gastric cavity, it strangely resembles
many Cuninae, and in bud-
ding from the manubriun, ©
it approaches the Antho-
medusae. No hydroid stage
has been observed in its life-
history.

Limnocodium, on_ the
other hand, resembles more |
closely Leptomedusae and
Trachomedusae (Figs. 52,
53). Its generative organs, of
which the male only have
been observed, are placed on
the radial canals, as in both
these orders; but it has a
hydroid stage, a thing not
known in any Tracho-

Fie, 55a.—Diagram of the gemmation of the medu- medusan known not to
soid of Limnocodium. a, external ectoderm ; b, endo- =,

derm of the radial canals ; c, coelenteron of the hydroid; occur In many Trachome-
d, cavity of radial canal; e, ectoderm of manubrium ; :

f rudiment of subumbral cavity; g, cavity of manu- dusae, and probably universal
brium ; A, endoderm of manubrium, with a canals among Leptomedusae ; yet

Dy Bee p n. (After Fowler.
(j); i, k, ectoderm of entocodon. (Aft er.) the firm character of (tha

bell and tentacles suggest Trachomedusan affinities,

2es

a GP om &

THE HYDROMEDUSAE 49

The continuation of the tentacles along the exumbral surface into a
“root,” which occurs in both of the freshwater genera, although not quite
of the character known in Trachomedusae and Narcomedusae, is never-
theless suggestive, and the presence of some-
thing corresponding to peronia points in the
same direction.

As regards the character of the sense organs,
which are of great diagnostic value throughout
the class, Limnocodium and Limnoenida agree
with each other in possessing similar organs, of
a type not known in any other Hydromedusan.
These organs (Fig. 54) resemble tentaculocysts
in possessing an endodermal axis, but differ
from them in position and in not secreting
an otolith ; they lie each in a closed vesicle
lined by ectoderm and surrounded by meso-
cloea. The vesicle in Limnocnida is situated
in the exumbral nettle-ring at the base of the
velum, and in Limnocodium, in the base of
the velum itself, into which latter it is con-
tinued as a long canal. It may perhaps be
eventually shown that a modification of cordyli
in one direction has resulted in the produc-
tion of these organs, in another in the forma-
tion of tentaculocysts.

Microhydra and Protohydra.

These two forms of uncertain position
need only brief mention.
They agree with the hy-
droid of Limnocodium in
the absence of tentacles,
While Microhydra (Ryder,
24) reproduces by lateral

Fic. 55).

Protohydra Leuckartii, expanded,
contracted, and in strobilation
(after Greef),

-gemmation, Protohydra (Greef, 24)
undergoes a process of transverse
strobilation.

Tetraplatia (Tetrapteron) volitans.

Fia. 55e.

Tetraplatia volitans (after Viguier).

This remarkable organism
(Viguier, 47) of marine habitat has been recorded by four observers only.

50 THE HYDROMEDUSAE

It is of elongate form, with a mouth at the lower pole. In section it is
somewhat square for the greater part of its length, but nearly midway
between the oral and aboral pole the body is constricted by a groove ; at
this point the tissues of the four angles of the square section are continued
across the constricting groove as flying buttresses. In the groove and
between the buttresses spring four bilobed paddles or wings, each lobe
carrying an otocyst. The ectoderm is ciliated and provided with nemato-
cysts. The coelenteron, otherwise simple, is continued through ‘the
buttresses ; the endoderm of the paddles is solid. While the nematocysts
and otocysts undoubtedly place this form with Hydrozoa, its exact position
has yet to be determined. Nothing is known of its development.

APPENDIX TO HypromMEDUSAE. No, II.
Graptolithidae.

The forms generally included in this class are known only in a fossil
state, and are divided into three orders, which possibly bear but little
genetic affinity to one another.

OrpeR 1. Dendroidea. These forms often exhibit a marked re-
semblance to Sertularian colonies (Dendrograptus). The zooids appear to
have been often dimorphic ; in Dictyonema rarum each branch presents
a common canal, from which are given off pairs of dimorphic thecae open-
ing in opposite directions (? hydrotheca and gonotheca).

OrvDER 2. Graptoloidea. These forms possess also a tubular skeleton
with a common canal, and thecae of an apparently Sertularian type. The
stem is stiffened by a solid axis (virgula) which lies in a groove of the
perisare. The theca of the primary zooid (sicula) does not increase con-
tinuously in length. In this group also there appears to have existed a
dimorphism, pear-shaped capsules (Dawsonia, Fig. 56°) being often found
close to or attached to a Graptoloid. The sicula when perfect exhibits two
regions—a smaller, slighter, embryonic chamber, continuous with which is
a stronger, larger, and darker chamber ; the mouth of the latter is gener-
ally provided with a spine,

Sus-OrpeR 1. Monoprionidae (Fig. 56'***), The thecae in this

sub-order are arranged on one side of the axis only. The sicula may face
either in the same direction as the mouths of the other thecae (Mono-
graptidae, Leptograptidae) or in the opposite direction (Dichograptidae,
Dicranograptidae). The second theca is budded from the sicula, the third
from the second, and so forth, a common canal placing the thecae in
communication with one another.

Sup-Orper 2. Diprionidae (Fig. 56%"). The thecae in this group are
arranged on two or four radii from the axis. These forms are linked with
the Monoprionidans by (a) Dicranograptus, the colony of which is at first
Diprionidan, and later bifurcates into two Monoprionidan stems, and by
(0) Dimorphograptus, in which the stem is at first Monoprionidan, then
Diprionidan. The colony may exhibit two (Diplograptidae) or four
(Phyllograptidae) rows of thecae ; the virgula is centrally placed, and each
row of thecae generally has a separate common canal of communication

—

7 i

—_~

THE HYDROMEDUSAE 51

between its members, the canals communicating below with each other
and with the sicula. The sicula faces in a direction opposite to that of
the other thecae.

There is some ground, at present most insecure, for the belief that, in
both Monoprionidae and Diprionidae, the individual stems were united
into colonies, and sprang from a central mass, the sicula being at the distal
end of each stem. The Graptoloids range from the Lower Arenig beds up
to the Silurian inclusive, and it would appear from their distribution that

S

Pia. 56.

Diagrams illustrating the structure and development of Graptolites. 1, Monograptus
priodon (after Nicholson); 2, longitudinal, and 38, transverse sections of Monograptus
priodon ; 4, transverse section of Phyllograptus ; 5, base of colony of et es i. ge minutus,
a two-branched Monoprionidan (after Wiman); 6, Graptolites with supposed gonangiuin
(Dawsonia) in place (after Hoernes); 7, base of colony of Diplograptus (after Wiman); 8, part
of colony of Retiolites, the perisarcal meshwork has been left on one theca only (after Holm);
9, transverse section of Retiolites, showing two thecae, the common canal, and the perisarcal
meshwork growing out from the lip of each theca. CC, common canal; S, sicula; 8’, mouth of
sicula; 7’, theca; V, virgula; V’, zigzag virgula of Retiolites; II, II, IV, etc., indicate suc-

_ cessively formed thecae, S being the first formed.

the Diprionidan forms are the older, the Monoprionidan forms having
arisen by the suppression of a row of thecae.

OrvER 3. Retioloidea (Fig. 56%°). This group, which is well
developed in the Ordovician rocks, includes Graptolites which have no
true sicula, but are characterised by the periderm forming an open mesh-
work. The thecae are generally arranged in two series; one or two
virgulae may be developed.

52 THE HYDROMEDUSAE

CLASSIFICATION AND LIST OF THE GENERA OF
HY DROMEDUSAE.

It is not at present possible to furnish a satisfactory classification of
the Anthomedusae and Leptomedusae. The systems of Hincks and of
Allman are based on hydroid structure, that of Haeckel on medusoid
structure ; our knowledge of the ontogenetic connection between indi-
vidual hydroids and medusoids is at present so small that any attempt to
combine the two systems must necessitate failure. The double systems,
hydroid and medusoid, are therefore here given separately; where
practicable, each generation has the corresponding generation appended in
brackets ; but even in the few cases here cited, the assignment of hydroid
to medusoid, and contrariwise, is often a matter of inference rather than
of proof. No attempt has been made in the present article at a critical
treatment of the current systems. The chief authorities utilised in this
classification are Allman (2), Haeckel (4, 39), Hincks (7), Moseley (37).
Another system of the Anthomedusae is to be found in Vanhéffen’s Versuch
einer natiirliche Gruppirung der Anthomedusen, Zool. Anz. xiv. 1891.
Several genera are thrown together and medusoids assigned to hydroids
on the authority of Browne’s British Hydroids and Medusae (Proce. Zool.
Soc. 1896). .

Nore. + unites various hydroid genera attributed to the same medusoid genus, or various
medusoid genera attributed to the same hydroid genus.
{] Square brackets indicate the corresponding medusoid genus in the hydroid scheme, or the
corresponding hydroid genus in the medusoid scheme.

= indicates a synonym.
S indicates a sessile gonophore, in contrast to a free-swimming medusoid.

CLASSIFICATION OF HYDROMEDUSAE.
Orper 1. Anthomedusae=Gymnoblastea. (For definition, see p. 11.)
(a). Medusoid Scheme.

Famity 1. Coponrpar. Genera—Codonium, Hkl., + Sarsia, Lesson,
+ Syndictyon, A. Agass., [Syncoryne]; Ectopleura, L. Agass., [Ectopleura] ;
Dipurena, M‘Crady, = Slabberia, Forbes ; Bathycodon, Hkl.; Dicodoniwm,
Hkl.; Dinema, v. Bened., [Perigonimus]; Steenstrupia, Forbes, + Hybo-
codon, L. Agass., = Amphicodon, Hkl., = Diplura, Allm., + Amalthaea,
O. Schmidt, [Corymorpha]; Euphysa, Forbes, [Halatractus]; Globiceps,
Ayres, [Pennaria} Faminy 2. Trartpar. Genera—Protiara, Hk1L;
Modeeria, Forbes; Corynetes, M‘Crady, [Halocaris]; Amphinema, Hk1.,
[? Perigonimus]; Codonorchis, Hkl.; Stomotoca, L. Agass.; Pandaea, Less. ;
Conis, Brandt; Tiara, Less., [Perigonimus] ; Turris, Less. [Turris = Clavula);
Catablema, Hkl.; Turritopsis, M‘Crady, = Callitiara, Hkl. Fasuty 3.
MARGELIDAE. Genera—Cytaeis, Esch.,= Margellium, Hkl., + Cubogaster,
Hk1., + Dysmorphosa, Phil., + Lizzia, Forb.(pars.), [Podocoryne] ; Cytandraea,
HKL, [Rhizocline] ; Lizusa, Hkl. ; Lizzella, Hkl. ; Thamnitis, Hkl. ; Thamno-
stylus, Hkl. ; Thamnostoma, Hkl. ; Limnocea, Péron ; Margelis, Steenstr., +
Hippocrene, Mertens, [Bougainvillea] ; Nemopsis, L. Agass.; Rathkea, Brandt.

Dele erteetemnctnnneemeemmatntmen ae

THE HYDROMEDUSAE 53

Famity 4. CLADONEMIDAE. Genera—Pteronema (? a Codonid), Hkl. ; Zan-
clea, Gegenb.; Gemmaria, M‘Crady [Gemmaria]; Eleutheria, Quatref.,
[Clavatella]; Ctenaria, Hkl.; Dendronema, Hkl.; Cladonema, Duj.,
[Cladonema = Stawridium] (? a Codonid) ; Willsia, Forbes, [Lar].

(b). Hydroid Scheme.

Faminy 1. Cravipar. Genera—Olava, Gmel. [S]; Rhizogeton, A. Ag.
[S]; Cordylophora, Allm. [S]; Tubiclava, Allm. [S]; Merona, Norm. [S].
Faminy 2. Turrmar. Genera—Turris, Less. = Clavula, Str. Wright,
[Turris]; Campaniclava, Allm. [8S]; Corydendriwm, van Ben. [?]; Dendro-
clava, Weismann, [Dendroclava] (? Pandaeid). Faminy 3. CoRYNIDAE.
Genera — Coryne, Girtn. [S]; <Actinogoniwm, Allm. [S]; Syncoryne,
Ehrenb. (pars.),[Codoniwm + Sarsia + Syndictyon] ; Gymnocoryne, Hincks [?] ;
Corynetes, M‘Crady, [Corynetes = Halocaris]; Gemmaria, M‘Crady, [Gem-
maria]; Sphaerocoryne, Pictet [7] Famiy 4. BouGaINvILLIDAE. Genera
—Bougainvillea, Less., [Margelis + Hippocrene]; Pertgonimus, M. Sars.,
[Dinema +? Amphinema]; Bimeria, 8. Wright [S]; Dzcoryne, Allm., [S];
Stylactis, Allm. [8S]; Garveia, S. Wright [S]; Wrightia, Allm., = Atractylis,
S. Wright [S] ; Hydranthea, Hincks [S]; Heterocordyle, Allm. [S]; Czonistes,
S. Wright [S]; Stylactella, Hkl. [?7]. Faminy 5. EUDENDRIIDAE. Genus
—Eudendrium, Ehrenb. pars. [S} Famiy 6. PENNARIIDAE. Genera—
Pennaria, Goldf., [Globiceps]; Stawridiwm, Duj., [Cladonema]; Halocordyle,
Alln., [Halocordyle] ; Vorticlava, Alder [?] ; Heterostephanus, Allm., [ Hetero-
stephanus]; Acharadria, 8S. Wright [?]; Ttarella [Tiarella], Famiy 7.
CLAVATELLIDAE. Genus—Clavatella, Hincks, [Eleutheria], Famity 8.
CLADOCORYNIDAE. Genus—COladocoryne, Rotch [?} Famiry 9. Tusu-
LARUDAE. Genera—Tubularia, Linn. pars. [S]; Ectoplewra, A. Agass.,
{Ectopleura}. Famity 10. MyriorHenipar. Genus—Myriothela, M. Sars
{S} Fasimy 11. Hypractinimar. Genus—Hydractinia, v. Bened. [S].
Famity 12. Popocorynrpar. Genera—Podocoryne, M. Sars, pars., [Cytaets
+ Cubogaster + Dysmorphosa + Lizzia (pars.)]; Corynopsis, Allm., [Corynop-
sis} Famiiy 13. CorYMORPHIDAE. Genera—Corymorpha, M. Sars, pars.,
[Steenstrupia + Hybocodon = Amphicodon = Diplura + Amalthaea]; Hala-
tractus, Allm., [Euphysa]. Famtty 14. MonocauLipar. Genus—Mono-
caulus, Allm. [S} Famiry 15. HyprotarmarE. Genus—Lar, Gosse,
[Willsia, vulgo Willia}. Famiuy 16. Monopracwiipar. Genus—Mono-
brachiwm, Merej. [?]. [Famiry Sponeicormar. Genera—(Spongicola,
F. E. Schulze, = Stephanoscyphus, Allin., is probably a Scyphistoma).]
Famity 17. Hyprimar. Genus—Hydra, Linn. [S]. Famiy 18. Myrronr-
MIDAE. Genus—Myrionema, Pictet. Fairy 19. CERATELLADAE. Genera
—Ceratella, Gray [S]; Dehitella, Gray [S] Incertar sep1s—Protohydra,
Greef; Microhydra, Potts.; Haleremita, Schaudinn ; Acaulis, Stimps.

Orver 2. Leptomedusae =Calyptoblastea. (For definition, see p. 22.)
ad (a). Medusoid Scheme.

Fairy 1. THAUMANTIIDAE. Genera—Tetranema, Hkl. ; Dissonema,
Hkl.; Octonema, Ukl.; Thawmantias, Esch., [Campanularia, ete.] has

|

54 THE HYDROMEDUSAE

exploded into numerous genera; Stawrostoma, Hkl.; Laodice, Less.,
[Lafoea]; Melicertella, Hkl.; Melicertissa, Hkl.; Melicertum, A. Agass.
[Melicertum]; Melicertidiwm, Hkl.; Orchistoma, Hkl.; Halmomises, v.
Kenn. Famrny 2. Cannotrpar. Genera—Staurodiscus, HkL; Gonynema, A.
Agass.; Ptychogena, A. Agass. ; Stawrophora, Brandt ; Polyorchis, A. Agass.;
Cannota, Hk. ; Dyscannota, Hkl. ; Berenice, Pér. et Lesueur ; Diplewrosoma,
Boeck, = Ametrangia, Allm.; Dicranocranna, Hkl.; Toxorchis, Hk. ;
Willetta, Hk1; Willsia (vulgo Willia, formerly classed here, but an Antho-
medusan), Forbes ; Proboscidactyla, Brandt ; Cladocanna, Hk). Famity 3.
Evcoripar. Genera—Lucopium, HkL, [Clytia] ; Saphenella, Hkl. ; Eucope,
Gegenb., [? Campanularia +? Clytia]; Obelia, Pér. Lesueur, [Obelia];
Tiaropsis, L. Agass.; Euchilota, M‘Crady, = Thawmantias (pars, = Laodice
(pars); Phialum, Hkl. ; Phialis, Hkl.; Mitrocomiwm, Hkl.; Epenthesis,
M‘Crady, [Clytia] ; Mitrocomella, Hk1. ; Phialidiwm, Leuck., = Thawmantias
(pars.), [Campanulina]; Mitrocoma, Hkl.; Eutimium, Hkl.; Eutima,
M‘Crady ; Saphenia, Esch.; Eutimeta, Hkl.; Eutimalphes, Hkl.; Octor-
chidium, Hkl.; Octorchis, Hkl. ; Octorchandra, Hkl; Jrentwm, Hk1. ; Irene,
Esch.; Tima, Esch. [Tima]. Famity 4. Arquormar. Genera—Octo-
canna, Hkl.; Zygocanna, Hkl.; Zygocannota, Hkl.; Zygocannula, Hk1. ;
Halopsis, A. Agass.; Aequorea, Pér. Les. ; Rhegmatodes, A. Agass. ; Stomo-
brachium, Brandt ; Stawrobrachiwm, Hkl. ; Mesonema, Esch., = Zygodactyla,
Brandt, [Zygodactyla]; Polycanna, Hk1., [Campanulina).

()). Hydroid Scheme.

Famity 1. CAMPANULARIIDAE. Genera—Campanularia, Lamk.,
[Thawmantias (pars)]; Lovénella, Hincks [?]; Obelia, Pér. Les. [Obelia] ;
Thyroscyphus, Allm. [7]; Hypanthea, Allm. [S]; Calycella, Hincks [S];
Lytoscyphus, Pictet [7]; Gonothyraea, Allm. [S]; Clytia, Lamx., [Eucope
(pars), + Epenthesis]; Campanulina, v. Bened., = Laomedea, Lamx., [Phia-
lidium + Polycanna]; Opercularella, Hincks [8S]; Calamphora, Allm. [S}];
Hebella, Allm. [?]; Halisiphonia, Allm. [8S]; Zygodactyla, Brandt, [Zygo-
dactyla = Mesonema]; Leptoscyphus, Allm. [?]; Obelaria, Hartlaub [S].
FaMILy 2. PrRIsIPHONIIDAE. Genera—Perisiphonia, Allm. [?]; Crypto-
laria, Busk [?]; Lafoea, Agass., [Laodice] ; Lictorella, Allm. [?]; Cuspidella,
Hincks [?]; ilellwm, Hincks [?]. Famiry 3. Hanecipar, Genera—
Halectwm, Oken [S]; Dzplocyathus, Allm. [?]; Ophiodes, Hincks [S];
Hydrella —[S]; Haloitkema, Bourne [?]. Fammy 4. SerruLaRmDAE
(gonophores sessile throughout). Genera—Sertularia, Linn. pars. ;
Diphasia, L. Agass.; Thuwiaria, Flem.; Desmoscyphus, Allm.; Sertularella,
Gray ; Hydrallmania, Hincks; Hypopyxis, Allm.; Stawrotheca, Allm.;
Dictyocladium, Allm. Famiiy 5. AGLAOPHENTIDAE (gonophores probably
sessile throughout). Genera—Aglaophenia, Lamouroux ; Acanthocladium.
Allm. ; Lytocarpus, Kirchenp. ; Streptocaulus, Allm. ; Diplocheilus, Allm. ;
Cladocarpus, Allm. Famity 6. HaLicornartmar (gonophores probably
sessile throughout). Genera—Halicornaria, Busk, pars. ; Azygoplon, Allm.
Famity 7. Iptpar. Genus—ZJdia, Lamouroux [S]} Famiry 8. Gram-
MARIIDAE. Genus—Grammaria, Stimps.,=(?) Salacia, Lamouroux [7].
FamILy 9, SyNTHECIDAE. Genera—Synthecium, Allm. [?]; Thecocladiwm,

a —

THE HYDROMEDUSAE 55

Allm. [7] Famiry 10. PLUMULARIIDAE (gonophores probably sessile
throughout). Genera — Plumularia, Lamk. pars.; <Antennularia,
Lamk.; Acanthella, Allm.; Schizotricha, Allm.; Sciurella, Allm.;
Polyplumaria, G. O. Sars ; Heteroplon, Allm.; Nemertesia. Famity 11.
CALICARPIDAE. Genera—Calicarpa [?]; Hippurella, Allm. [7]. Famiy 12.
HyYDROCERATINIDAE. Genus—Clathrozoon, Spencer [7]. INcERTAE sEDIS
—Trichydra, 8. Wright [7]; Coppinia, Hassall [?}.

OrveR 3. Trachomedusae. (For definition, see p. 30.)

Faminy 1. Prrastmpar. Genera— Petasus, Hkl.; Dipetasus, Hkl. ;
Petasata, Hkl. ; Petachnuwm, Hk. ; Aglauropsis, F. Mill.; Gossea, L. Agass. ;
Olindias, F. Mill. Faminry 2. TRACHYNEMIDAE. Genera—Trachynema,
Gegenb.; Marmanema, Hkl.; Rhopalonema, Gegenb.; Pectyllis, Hkl. ;
Pectis, Hkl. ; Pectanthis, Hkl. ; Homoeonema, Maas. ; (?) Pantachogon, Maas.
Famity 3. AGLAuRIDAE. Genera—Aglantha, Hkl.; Aglawra, Pér. Les. ;
Agliscra, Hkl.; Stawraglaura, Hkl.; Persa, M‘Crady. Famity 4. Gerry-
ONIDAE. Genera—Liriantha, Hkl.,=Liriope, Less.; Glossoconus, Hkl. ;
Glossocodon, Hkl.; Geryones, Hkl.; Geryonia, Pér. Les. ; Carmaris, Hkl. ;
Carmarina, Hk].

ORDER 4. Narcomedusae. (For definition, see p. 33.)

Famity 1. CUNANTHIDAE. Genera—Cunantha, Hkl.; Cunarcha, Hk1.;
Cunoctantha, Hkl.; Cunoctona, Hkl.; Cunina, Esch.; Cunissa, Hk).
Famity 2. PeGANTHIDAE. Genera—Polycolpa, Hkl. ; Polyxenia, Esch. ;
Pegasia, Pér. Les.; Pegantha, Hkl. Faminy 3. ArGinipaE. Genera—
Aegina, Esch. ; Aeginella, Hkl.; Aegineta, Gegenb. ; Aeginopsis, Brandt ;
Aeginura, HkL ; Aeginodiscus, Hkl.; Aeginodorus, Hkl. ; Aeginorhodus,
Hkl. Famity 4. Sotmartpar. Genera—Solimissus, Hkl.; Solmundus,
Hkl. ; Solmundella, Hkl. ; Solmoneta, Hkl.; Solmaris, Hk1.

OrveR 5. Hydrocorallinae. (For definition, see p. 35.)

Famity 1. Mitierorrmar. Genus— Millepora, Linn. Faminy 2.
STYLASTERIDAE. Genera—Sporadopora, Moseley ; Pliobothrus, Pourtal.;
Lrrina, Gray; Distichopora, Lamk.; Labiopora, Moseley ; Spinipora,
Moseley ; Allopora, Ehrenb.; Stylaster, Gray ; Stenohelia, S. Kent ;
Conopora, Moseley ; Cryptohelia, M. E. and H.; Astylus, Moseley.

Orver 6. Siphonophora. (For definition, see p. 38.)
Susp-OrpER 1. DISCONECTAE.

Definition —Siphonophora with an apical chambered pneumatophore,

_ without nectophores or bracts. The individuals are confined to the lower

surface of the pneumatophore, and are a single central gastrozooid,
surrounded by concentric girdles of blastostyles and dactylozooids.

4 Famity 1. Discanipar. Genera—Discalia, Hkl.; Disconalia, Hkl.

a

56 THE HYDROMEDUSAE

Famity 2. Porprripar. Genera—Porpalia, Hkl.; Porpema, Hkl.; Por-
pitella, Hkl. ; Porpita, Lamk. Famity 3. VELELLIDAE. Genera—Lataria,
Esch. ; Velella, Lamk.; Armenista, Hk].

Sus-ORDER 2. CALYCONECTAE.

Definition —Siphonophora without pneumatophore, with one or more
nectophores. The coenosare is elongated and tubular, and carries the
cormidia which may become freed as Eudoxomes or Ersaeomes (+ Mono-
gastricae).

Famity 4. Monopaympar. Genera—Monophyes, Claus ; Sphaeronectes,
Huxl. ; Cymbonectes, Hkl.; Muggiaea, Busch ; Cymba, Esch. ; Doramasia,
Chun; Halopyramis, Chun. Famity 5. Dipnyrpar. Genera—Praya,
Blainv. ; Lilyopsis, Chun; Galeolaria, Lesueur; Diphyes, Cuv.; Mitro-
phyes, HkL. ; Diphyopsis, Hkl.; Abyla, Quoy Gaim. ; Bassia, Quoy Gaim. ;
Calpe, Quoy Gaim. ; Amphicaryon. FAMILy 6. STEPHANOPHYIDAE. Genus
Stephanophyes, Chun. Famity 7. DresMopayrpar. Genera— Desmalia,
Hk1. ; Desmophyes, Hkl. Famtny 8. Potypaympar. Genera—Hippopodius,
Quoy Gaim. ; Polyphyes, Hkl.; Vogtia, Koll.

[Famiry Evpoxrpae (includes free Eudoxomes of other genera, the
names of which are included in square brackets). Genera—Diplophysa,
Gegenb., [Sphaeronectes] ; Eudoxella, Hk1., [Praya] ; Cueubalus, Quoy Gaim.,
[Muggiaea]; Cucullus, Quoy Gaim., [Diphyes]; Cuboides, Quoy Gaim.,
[Cymba]; Amphirrhoa, Blainv., [Abyla]; Sphenoides, Huxl, [Bassia] ;
Aglaisma, Esch., [Calpe]. Famity Ersarmar (includes free Ersaeomes of
other genera, the names of which are included in square brackets).
Genera—Ersaea, Esch., [Diphyopsis]; Lilaea, Hk1., [Lilyopsis}]

SuB-ORDER 3. PHYSONECTAE.

Definition —Siphonophora with an apical pneumatophore, followed
by one or ‘more coronae of nectophores or bracts, without aurophore.
The coenosare is elongated and tubular, and carries the cormidia.

Faminy 9. Crrcanmpar. Genus—Cirecalia, Hkl Famimy 10.
ATHORIIDAR. Genera—Athoria, Hkl.; Athoralia, Hkl. Faminy 11.
APoLEMIIDAE. Genera—Dicymba, Hkl.; Apolemia, Esch. ; Apolemopsis,
Brandt. Famity 12. AGALMIDAE. Genera—Stephanomia, Pér. Les. ;
Crystallodes, Hkl. ; Phyllophysa, L. Agass.; Agalma, Esch. ; Anthemodes,
HklL ; Cuneolaria, Eysenh.; Halistemma, Huxl. ; Cupulita, Quoy Gaim. ;
Agalmopsis, M. Sars; Lychnagalma, Hkl. Famity 13. ForsKALIDar.
Genera—Strobalia, Hkl.; Forskdlea, KOll.; Forskaliopsis, Hkl.; Bathy-
physa, Studer. Famity 14. Necratipar. Genera— Nectalia, Hk. ;
Sphyrophysa, L. Agass. Famity 15. Discorasrpar. Genera—Physophora,
Forsk. ; Discolabe, Esch. ; Stephanospira, Gegenb. Famity 16. ANTHOPHY-
sIpaAE. Genera—Rhodophysa, Blainv.; Melophysa, Hkl.; Athorybia, Esch. ;
Anthophysa, Mertens.

Sup-Orprer 4. AURONECTAE.

Definition—Siphonophora with an apical pneumatophore, followed
by coronae of nectophores, and carrying an aurophore. Individuals con-

.

fined to the lower surface of the colony, including numerous gastro-
zooids.

Famity 17. SrerHatmpare. Genera—Stephalia, Hkl.; Stephonalia,
Hkl. Famiy 18. Raopatimpar. Genera—Auralia, Hkl.; Rhodalia,
Hkl.; Angelopsis, Fewkes.

LITERATURE OF THE HYDROMEDUSAE 57

Sup-OrDER 5. CYSTONECTAE.

Definition.—Siphonophora with an apical hollow pneumatophore,
without nectophores or bracts. Gastrozooids generally numerous,
arranged either on the lower side of the pneumatophore, or on a long
tubular coenosare.

Famity 19. Cysranimpar. Genus—Cystalia, Hkl. Faminy 20. Ratzo-
PHYSIDAE. Genera— Aurophysa, Hkl.; Cannophysa, Hkl.; Linophysa,
Hkl.; Nectophysa, HklL; Pnewmophysa, Hkl.; Rhizophysa, Pér. Les. ;
Pterophysa, Studer; Plewrophysa, Fewkes. Famity 21. SALAcrIDAr.
Genus—Salacia, Hkl. Famiiy 22. Eprpunipar. Genera—Epibulia, Esch. ;
Angela, Less. Famity 23. Puysanmpar. Genera—Alophota, Brandt ;
Arethusa, Hkl.; Physalia, Lamk.; Caravella, Hkl.

Incertae sedis.

(Hydromedusae which are not referable to any known order of the
group.)

Limnocodium, Allm.; Limnocnida, Giinth.; Protohydra, Greef ;
Microhydra, Potts ; Tetraplatia, Busch.

LITERATURE OF HyDROMEDUSAE.

As far as possible only one paper on each special subject has been cited, in
which the student will find references to the earlier literature.
The general subject :—
1. Allman. Monograph of the Gymnoblastic or Tubularian Hydroids, 1871-72.
2. Allman. Chall. Rep. Zool. vii. (Hydroidea, pt. i.); xxiii. (Hydroidea,
pt. ii.).
3. Chun. Bronn’s Klassen und Ordnungen des Thierreichs. Coelenterata,
1889 (in progress).

4. Haeckel. System der Medusen, 1879-80.

5. Haeckel. Chall. Rep. Zool. iv., Deep Sea Medusae, 1882.

6. Hertwiy. Organismus der Medusen. Denkschr. Gesell. Jena, ii. 1878.
7. Hincks. British Hydroid Zoophytes, 1868.

8. Jackson. Forms of Animal Life, pp. 745-780, 1888.

9. Lankester. Encyclopaedia Britannica, ed. ix., article ‘‘ Hydrozoa,” 1881.
10. Weismann. Enstehung der Sexualzellen bei den Hydromedusen, 1883.

Embryology :—
* 11. Balfour. Treatise on Comparative Embryology, 1880-81.
12. Korschelt and Heider. Text-book of the Embryology of Invertebrates. Eng.

trans., 1895-99.
13. Metschnikof. Embryologische Studien an Medusen, 1886.

18

9

58 LITERATURE OF THE HYDROMEDUSAE

Special subjects :—

14. Brooks. (Life History of Hydromedusae.) Mem. Bost. a
Soe. N. H. iii., 1886. } Motageness.
15. Braem. (Ueber d. Knospung bei mehrschichtige
Thieren.) Biol. Centr. xiv., 1894. lecmanans of
16. Seeliger. (Verhalten d. Keimblatter b. d. Knospung d. hydroid.
Coelenteraten.) Zeit. wiss. Zool. lviii., 1894. |
17. Jickeli. (Der Bau der Hydroidpolypen, I.) Morph.
Jahrb. viii., 1882. | :
18. Von Lendenfeld. (Ueber Coelenteraten der Siidsee, I.) Histology.
Zeit. wiss. Zool. xxxvii., 1882. |
19. Hertwig, O. and &. Nervensystem und Sinnesorgane
der Medusen, 1878. |
20. Himer. Die Medusen . . . auf ihr Nervensystem
untersucht., 1878.
21. Brooks. (The Sense Clubs or Cordyli of Laodice. |
Journ. Morph. x., 1895.
22. Driesch. (Rectoniashs Studien an Hydroid-polypen.) Architecture of
Jen. Zeitschr. xxiv-v., 1889-91. colony.
23. Nutting. (Notes on the Reproduction of Plumularian
Hydroids.) Amer. Nat. xxix., 1895.

Nervous system
and sense-organs.

Special groups and genera :—

24. Ryder. (Development and Structure of mais ; ;
Ryderi.) Amer. Natur., 1885. Microhydra.

24a. Greef. (Eine Marine Stammform der eee: eee otohydra.
Zeit. wiss. Zool. xx., 1870.

25. Hardy. (Histology and Development of ae) ie athaka:
Quart. Journ. Micr. Sci. xxxii., 1891.

26. Colleutt. (Structure of Hydractinia echinata. ) peer ae
Journ. Micr. Sci. xl., ‘1897. Hydractinia.

27. Spencer. (Structure of Ceratella fusca.) Trans. R.
Soc. Victoria, 1891. | coratella

28. Haeckel. Deep Sea Keratosa. Chall. Rep. Zool. xxxii. Spongicolidae.

29. Wagner. (Organisation des Monobrachium ee ae
cum.) Zool. Anz. xii., 1889. a Sa

30. Ussow. (Eine neue Form von Siisswasser-Coelenteraten. ) :
Morph. Jahrb. xii., 1887. } Polypodium

31. Jickeli. (Der Bau der Hydroid-polypen, II.) Morph.
Jahrb, viii., 1882.

32. Spencer. (A New Family of Hydroidea.) Tr. R. Soc.
Victoria, 1890.

33. Von Lendenfeld. (Ueber Coelenteraten der Siidsee, III.)
Zeit. wiss. Zool., xxxviii., 1883.

34. Lang, Arn. (Gastroblasta Raffaeli.) Jen. Zeitsch.
xix., 1886. Par ee

35. Brooks. (The Life History of Epenthesis M‘Cradyi.) Hucope in Hasion.
Stud. Biol. Lab. Johns Hopkins Univ. iv., 1888.

36. Sars, M. Beskriv. og Jagttag., 1835.

} Anisicola.
} Clathrozoon.

} Nematophores.

Thaumantias
budding.

LITERATURE OF THE HYDROMEDUSAE 59

37. Moseley. (Corals.) Chall. Rep. Zool. ii. 1881.

38. Hickson. (Development of Distichopora votes) | Hysol,
Quart. Journ. Micr. Sci. xxxv., 1893.

39. Haeckel. (Siphonophora). Chall. Rep. Zool. xxviii., 1888.

40. Chwn. (Die Canarischen Siphonophoren, I., II.) Abh.
senck. Ges. v., 1891-92.

41. Chun. (Bau u. morph. Auffassung d. Siphonophoren.) Siphonophora.
Verh. deutsch. zool. Ges., 1897.

42. Schneider. (Mitth. ii. Siphonophoren.) Zool. Jahrb.
(Anat. Ontog.), ix., 1896.

43. Pes (On Angelopsis.) Ann. Mag. N. H. (6), iv., tiecnbaian:

44. Maas. (Bau. u. Entwickl. d. Cuninenknospen.) Zool. } cane
Jahrb. (Anat. Ont.), v., 1892. es .

45. Giinther. (Minute Anatomy of Limnocodium.) Quart. } ee
Journ. Micr. Sci. xxxv., 1894. 1D .

46. Giinther. (Anatomy of Limnocnida ese ida
Quart. Journ. Micr. Sci. xxxvi., 1894. aa
47. Viguier. (Animaux inf.-de la Baie d’Alger, ney 2
* Arch. zool. exp. gén. (2), viii., 1890. So
48. Holm. (Gotland’s Graptoliter.) Bih. Svenska act |
Handl. xvi., 1890.

Graptolitidae.
49. Wiman. Bull. geol. Inst. Upsala, 1893. )

CHAPTER V.

THE SCYPHOMEDUSAE.!

CLASS SCYPHOMEDUSAE.

Order 1. Stauromedusae.

» 2. Peromedusae.
» o. Cubomedusae.
,, 4. Discomedusae.

Sub-Order 1. Cannostomae.
>i 2. Semostomae.
ie 3. Rhizostomae.

DEFINITION.—Coelenterata which typically present two main
forms of individuals—the non-sexual scyphistoma (hydroid) and

Fic. 1.

Longitudinal section of

a diblastula (gastrula),
formed by invagination ofa
simple blastula at one pole.
a, orifice of invagination
(blastopore); 6, coelen-
teron; c, endoderm; 4d,
ectoderm. (After Gegen-
baur, from Lankester.)

the sexual medusoid ; in this case the life-
history presents an alternation of generations
in which the scyphistoma produces the medu-
soid by transverse strobilation, and the sexual
cells of the medusoid develop into a scyphi-
stoma. In other cases the medusoid may
develop directly from the sexual cells. Gastric
ridges (taeniolae or mesenteries) occur in both
scyphistoma and medusoid, gastric filaments
(phacellae) in the medusoid. The sexual cells
lie typically in interradii, and are developed
from endoderm. The medusoids are devoid of
avelum; a velarium is sometimes present; the
sense organs are tentaculocysts and cordyli.
In the Scyphomedusae, as in the Hydro-
medusae, but by a different path, the seg-
mentation of the fertilised ovum produces a
larva of the diblastula type (cf. p. 2), the endo-

derm of which is formed by invagination, and not by delamination

from the ectoderm.

From this diblastula may grow either of two

forms of individual—the hydroid or the medusoid.
1 By G. Herbert Fowler, B,A., Ph.D.

THE SCYPHOMEDUSAE 61

The Seyphomedusan hydroid or scyphistoma (Fig. 6) is, com-
paratively speaking, insignificant in size and monotonous in
structure ; it is known only among Ephyroniae (Discomedusae), and
will be described under that group.

The medusoid (Figs. 4, 8) is, roughly speaking, of the same
type as that of the Hydromedusae—manubrium, tentacles, ex-
umbral and subumbral surfaces are of the same general character ;
but the velum is absent, its place being sometimes taken by the
velarium ; the latter may be either the inflected edge of the bell
(Aurelia), or a definite subumbral outgrowth containing coelenteric
canals (Charybdaea), but in neither case agrees with the Hydro-
medusan velum in position or in structure. The gastric cavity
exhibits four pouches, from which or from between which lead the
radial canals; the latter are separated by an endoderm lamella in
the essentially medusoid forms.

In the more scyphistomoid forms (Fig. 2') strong plates or
pillars of mesogloea run from body wall to stomodaeum, forming
the taeniolae or mesenteries, into which ectodermal pits (subumbral
funnels, subgenital pits) of varying depth penetrate from the oral
surface. The mesenteries do not appear in all cases to be formed
by endodermal concrescence.

The canals are often numerous; they frequently branch, and
sometimes anastomose ; they open into a circular canal at the edge
of the bell. Gastric filaments (phacellae), interradially placed,
are characteristic of this group of organisms. The generative
organs are interradial or adradial in position, and are derived from
endoderm cells.

ORDER 1. Stauromedusae.

DEFINITION.—Scyphomedusae which are devoid of tentaculo-
cysts, but in some cases have in their place marginal anchors. The
tentacles are perradial and interradial in position. The body is
more scyphistomoid than medusoid, exhibiting a stomodaeum
suspended by four mesenteries, between which lie the four broad
perradial pouches. There is no alternation of generations.

The Stauromedusae (Figs. 2, 3) are hypogenetic; the single
form of individual presents features intermediate between those
of hydroid (scyphistomoid) and medusoid forms. It is either
purely free-swimming (Tessera), or has the power of temporary
fixation (Haliclystus) by the aboral pole.

The organism is goblet-shaped, with a narrow stem which ends
conically (Tessera), or in a dise (Haliclystus) which can be used
_ for adherence to a solid object. The manubrium is well developed,

but no velum is present. ‘The edge of the bell is either (1) simple,
and provided with four perradial and four interradial tentacles

.

62 THE SCYPHOMEDUSAE

(Tessera), to which eight adradial (Tesserantha) or even more may
be added ; or else (2) is divided by incisions into eight hollow
adradial lappets ; on each lappet is seated a bunch of capitate
tentacles, and between the lappets lie perradial and interradial
marginal anchors or colletocystophores (Haliclystus, Fig. 3), which
are, however, absent in some genera (Lucernaria). The marginal
anchors are modified and shortened tentacles, at the base of each

Hf) ee
HH G
38
=¥

30

eA)

31

HI

Ht 2

scarassces

om

.
—

= ao”
Scorn - ==,
Ceprer wit verereeecieneee® =

Fic. 2.

Diagrams illustrating the structure of Lucernaria. 1, longitudinal section; the right
half passes along an adradius, just missing a mesentery, which is shown in thin outline
and carries gastric filaments and generative organs; the left half passes along an interradius
and shows the course of a subumbral pit deep into the substance of the mesentery. 2, transverse
section; the right half at the level of the stomodaeum, the left half a little below that level,
and through the upper part of the subumbral pits. 3, transverse section ; the right half through
the lower part of the subumbral pits, the left half through the base of the animal where the four
mesenteries fuse, centrally dividing the coelenteron into four pouches. In all three figures ecto-
derm is strongly hatched, endoderm lightly hatched, mesogloea black. C, coelenteron ; CC,
circular canal; G, genital organ; GF, gastric filament; J, interradius ; LM, ectodermal longi-
tudinal muscle band, continued aborally into the mesogloea ; M, mesentery ; P, perradius ; SP,
subumbral pit; S7', stomodaeum.

lies a pad of nematocysts and adhesive cells. No organs of
special sense are developed in this group.

The mouth, which is often frilled; leads into a tube, which is
probably a stomodaeuwm, or invagination of ectoderm. At the bottom
of the stomodaeum lies the gastric cavity, which is imperfectly
divided into four perradial chambers, homologous with the perradial
canals of Hydromedusae, by four interradial mesenteries or partitions

—

THE SCYPHOMEDUSAE 63

(taeniolae) ; these are projections of mesogloea and endoderm from
the exumbral body wall towards the centre of the cavity. The
coelenteron, thus divided, extends into the adradial lappets of the
edge of the bell. In most forms the mesenteries, which have
a free edge in the more central parts of the organism, become
attached to the subumbral wall in the oral region, and are also
continued into the lappets; they are, however, prevented from
reaching the extreme lip of the bell by a circular canal. In other
forms (Tessera) the mesenteries project but little from the exumbrellar
wall and have only a very short attachment to the subumbrella ;
the circular sinus is therefore very large. In many forms a pouch
of the ectoderm of the subumbrella, the interradial or subwmbral
funnel, penetrates far into each mesentery.

From the mesenteries grow the gastric filaments (phacellae) ; of
these there are four only, interradially placed (Tessera) ; or they
may be present in considerable numbers along both sides of each
mesentery (Haliclystus). In some cases the four mesenteries fuse
aborally in the centre of the gastric cavity.

A well-developed circular muscle runs round the edge of the bell in
all forms. Of the longitudinal muscles, the most marked are the eight
perradial and interradial bands, of which the latter le immediately
under the ectoderm of the subumbral funnels, and are continued
deep into the substance of the mesogloea of the mesentery aborally.

The sexes are separate. The generative organs are interradial,
and are horseshoe-shaped (Tessera), or are split by growth of the
mesenteries into bands at their sides (Haliclystus).

Little is known of the reproduction of this group. The blastula
is apparently converted into the diblastula by a process intermediate
between delamination and true invagination.

ORDER 2. Peromedusae.

DEFINITION.—Scy phomedusae with four interradial tentaculo-
cysts ; the tentacles are perradial and adradial in position. Four
mesenteries suspend the stomodaeum, and being attached to the
body wall at two points only, divide the peripheral coelenteron
into two large circular sinuses (confluent radial pouches). There is
no alternation of generations.

The Peromedusae (Fig. 4) are medusiform, and bear a strong
resemblance to the Tesseridae among Stauromedusae. The bell is
conical and carries a well-developed manubrium , no velum is present,
but a slight projection of the circular muscle subumbrally constitutes
the velarium. The edge of the bell has a complicated structure ; it
generally exhibits either four perradial tentacles, four tentaculo-
cysts on interradial lappets or pedalia, and eight adradial lappets

a

64 THE SCYPHOMEDUSAE

or pedalia (Pericolpa); or four interradial tentaculocysts, four
perradial and eight adradial tentacles on pedalia, and sixteen
subradial pedalia (Periphylla). The tentacles are long and hollow ;
the tentaculocysts are short, and present on the oral face a crescentic
pad of pigmented sense cells, a median ocellus, and a stalked sense
club with otoliths ; on the aboral face lies a pair of ocelli.

The mouth leads into a long tube, probably a stomodaewm, which
opens below into the gastric cavity. The latter is, as in Stauro-
medusae, imperfectly divided into four perradial chambers by four
interradial mesenteries, which are invaded by four interradial funnels
of the subumbrella. The mesenteries are attached to the ex-
umbral body wall only in the most aboral quarter of the bell,
and again at a point just below the union of stomodaeum and
gastric cavity ; there are thus left two large circular sinuses, one
round the subumbral funnels, the other round the edge of the bell.
In the pedalia at the edge of
the bell the circular sinus is

Fic. 3.

8.—Haliclystus, temporarily attached
to a piece of weed, showing eight bunches
of capitate tentacles and eight colleto-
cystophores.

4.—Periphylla mirabilis (after Haeckel).
The division of the exumbral surface into
pedalia is well shown. a, tentaculocyst
(interradial) ; b, subradial pedalia; four
perradial and eight adradial tentacles are
present.

further subdivided into eight, sixteen, or more pouches by fusion
of exumbral and subumbral walls. The phacellae are developed
at the sides of the mesenteries ; the generative organs form eight
horseshoe-shaped glands, placed adradially.

Nothing is known of the development of this group.

. ORDER 3, Cubomedusae.

DEFINITION.—Scyphomedusae with four perradial tentaculo-
cysts; the tentacles are interradial in position. Four laminar
mesenteries divide the peripheral coelenteron into four broad per-
radial pouches. There is no alternation of generations.

THE SCYPHOMEDUSAE 65

The Cubomedusae (Fig. 5) are medusiform only. The
umbrella is square in section and rounded above ; a broad velariwm,
containing endodermal canals and suspended by four perradial
frenulae, or thickenings of the subumbrella, is present in many forms
(Chi wy bdae: v), but is sometimes absent (Procharagma) or slightly
dev eloped (Procharybdis). The manubrium is four-square, its
angles lying perradially. Four inter-
radial fentacles, long, hollow, and eylin-
drical, are always present ; they are
generally seated on lappets (pedalia),
which in some cases carry numerous
additional tentacle 23 (Chirodropus).

P
E
F

Fic. 5.

Charybdaea marsupialis (after Claus). 1. The
four annulated tentacles are seen depending
from the four lappets placed at the four corners
of the quadrangular umbrella. These are inter-
radial. Two of the four perradial gastric pouches,
representing radial canals, are seen of a pale tint.
Fq, gastral filaments (interradial); R, the modified
perradial tentacles forming tentaculocysts ; G, cor-
ner ridge facing the observer and dividing adjacent
pouches of the umbrella; GF, position of one of the
genital bands. 2. View of the margin of the um-
brella of Charybdaea marswpialis (natural size, after
Claus). At the four corners are seen the lappets
which support the long tentacles, and in the middle
of each of the four sides is seen a tentaculocyst ;
lel, the vaseular velarium, with its branched
1 We vessels.

The nervous system is well developed, consisting of a sub-
umbrellar nerve ring, and of four larger perradial and four smaller
interradial ganglia, from which nerves pass to the sense organs,
muscles, and tentacles. The sense organs are fentaculocysts, they
are always four in number and perradial in position, and lie in
sense pits on the exumbrella. In Charybdaea each consists of a
short stalk, the head of which carries a terminal otocyst with
numerous crystalline otoliths, two median and two pairs of lateral
ocelli.

66 THE SCYPHOMEDUSAE

The tube of the manubrium leads into a short gastric cavity;
from this four broad shallow perradial canals or pouches, separated
by narrow interradial mesenteries, lead to the circular canal at the
edge of the bell. This canal is further subdivided by fusion of its
exumbral and subumbral walls into pouches, eight (Charybdaea)
or sixteen (Chirodropus) in number ; from these lead the canals
of the tentacles and velarium. The mesenteries are traversed
by an endoderm lamella, and carry interradial phacellae at their

Fic. 5a.

1. Horizontal section through the umbrella and
manubrium of Charybdaea marsupialis (modified
from Claus); Ma, manubrium; SR, side ridge (per-
radial); CR, corner ridges, separated by CG, the
interradial corner groove; Ge, the genital lamellae
in section, projecting from the interradial angles on
each side into UE, the radial canals of the umbrella ;
SU, the subumbral space. 2. Vertical sections of
( harybdaea marsupialis, to the left in the plane of an
interradius, to the right in the plane of a perradius ;
Ma, manubrium ; £Az2, gastric cavity ; Gh, gastral fila-
ments (placellae); CG, corner groove; SR, side ridge ;
EnL, endoderm lamella (line of concrescence of the
walls of the enteric cavity of the umbrella, whereby its
single chamber is broken up into four pouches); Ge,
line of attachment of a genital band; ZU, circular
canal, giving origin to TCa, the tentacular canal; Ve,
velarium ; Fr, frenum of the velum ; 7c, tentaculocyst.
(From Lankester.)

egal ELAN NET nag a .
) aud

)

aboral ends. In a few cases eight adradial arms carrying
digitate filaments grow out from the exumbral body wall,
and hang free in the radial canals (Chirodropus). As in Hali-
clystus, the generative organs grow out from the sides of the in-
terradial mesenteries, and form leaf-shaped projections into the
radial canals.

Practically nothing is known of the development of this

group.

THE SCYPHOMEDUSAE 67

ORDER 4. Discomedusae.
DEFINITION.—Scyphomedusae with four perradial and four
interradial (sometimes more) tentaculocysts. The radial canals
are either broad pouches or fine canals, and are often very

Fia. 6.

Later development of Chrysaora and Aurelia (after Claus). A, secyphistoma of Chrysaora,
with four perradial tentacles and horny basal perisare. JB, oral surface of later stage of
scyphistoma of Aurelia, with commencement of four interradial 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. D, first constriction of the Aurelia scyphistoma to form the pile of ephyrae or young
medusae (see Fig. 7). The single ephyra carries the sixteen scyphistoma tentacles, which will
atrophy and disappear. The four longitudinal gastric ridges are seen by transparency. EF, young
ephyra just liberated, showing the eight bifurcate arms of the disc and the interradial single
gastral filaments. F, ephyra developing into a medusa by the growth of the adradial regions.
The gastral filaments have increased to three in each of the foursets. A, margin of the mouth ;
Ad, adradial radius ; F, gastral filament; Jn, interradial radius ; JG, adradrial gastral canal ;
JR=R3, adradial lobe of the disc ; K, lappet of a perradial arm; M, stomach wall; Mst, muscle
of the mesentery ; Mw, mesentery; Ms, mesoderm; 0, tentaculocyst; P, perradial radius ;
R2, interradial radius ; R3, adradial radius ; SG, commencement of circular canal.

numerous; they are not separated from each other by laminar
mesenteries, and a well-marked endoderm lamella unites them.
Development showing alternation of an asexual scyphistomoid
with a sexual medusoid generation.

The Discomedusae are probably all a metagenetic hydroid-
like form alternating with a sexual medusoid generation. In

68 THE SCYPHOMEDUSAE

structure the “hydroid” differs considerably from that of the
Hydromedusae, and is for distinction termed the Scyphistoma
(scyphula).

STRUCTURE OF THE ScYPHISTOMA.—The gastrula, formed by
invagination from the blastula, having been converted into a closed
sac by coalescence of the lips of the blastopore, affixes itself to a
solid object, and a mouth is formed by an ingrowth of ectoderm
or stomodaeum, which perforates to the endodermal coelenteron,
The appearance of four perradial tentacles is followed by the forma-
tion of four interradial, and these by eight adradial tentacles ; all
sixteen tentacles are solid. In some cases more than sixteen are
developed. To this fixed tentaculate organism is applied the name
Scyphistoma (Figs. 6, 4, B, C, D; 7). In some cases it secretes

a perisare (Chrysaora).

Internally the organism presents
considerably greater complexity of
structure than the hydroid type of
Hydromedusae, being built essenti-
ally on the same plan as Haliclystus
among Stauromedusae. It has
four interradial mesenteries (faeni-
olae), which have a free edge pro-
jecting into the gastric cavity below,

-but are attached in the oral region
to the stomodaeum and subumbrella;

they are invaded for a short distance
by ectodermal subumbral funnels, the
muscle cells of which run deep into
the mesogloea. Phacellae or gastric
filaments are not developed, but the
thickened edge of the mesentery is
probably digestive in function, as in
the Anthomedusae.

The Scyphistoma multiplies (a)
by stolonar gemmation from creep-
ing horizontal stolons ; (2) by lateral
gemmation, the buds, which are
pushed out horizontally, bending

Fic. 7. vertically downwards, becoming
crcttghlating, gevmpictoms of, Anvtia attached to a solid object, and de-
stricted base of seyphistoma; 2, site of tached from the parent; (c) by
tentaculocyst; 8, adradial tentacle; 4, P °
marginal guard lappet of future tentaculo- strobilation.
= STROBILATION AND GROWTH OF
THE EpHyra.—tThe process of strobilation is apparently seasonal.
A series of transverse circular furrows constrict the upper or oral
part of the Scyphistoma (Fig. 7). In the uppermost of the seg-

es

.

THE SCYPHOMEDUSAE

69
ments thus indicated, eight bifid lobes grow outwards, each lobe
carrying with it the attachment of either a perradial or interradial
tentacle.

The bases of these tentacles are stated to be converted
into the tentaculocysts of the adult medusoid, the eight adradial

ri
goat
Ay

ry

Fic. 8.
Aurelia aurita, from the oral surface. 1, mouth; 2, perradial oral arms; 3, marginal
tentacles; 4, perradial branching canal; 5, adradial straight canal; 8, circular canal; 9, ten-
taculocyst; 11, interradial gastric filaments and generative organs.
position.

not shown in the drawing; the oral arms have been slightly twisted out of their perradial
(From Shipley, after Claus.)

The subgenital pits are

tentacles disappearing altogether. A prolongation of the coelen-
teron, which will form the axis of the future perradial and inter-
radial canals of the adult, runs out into each lobe. At about this
stage the entire segment becomes constricted off from the Scyphi-

stoma, and leads a free-swimming existence as an Lphyra, the
larval form of the future medusoid. Of the lower segments of

the Scyphistoma, some, if not all, may also put out sixteen ten-
tacles, and all become constricted off as Ephyrae. The basal
unconstricted part of the Scyphistoma is stated to become again
tentaculate, and to remain quiescent till the next season, when the
process of strobilation is repeated.
In the Ephyra (Fig. 6, Z, F) the adradial spaces between the
lobes gradually fill up by centrifugal growth of the disc, and eight

'

70 THE SCYPHOMEDUSAE

adradial canals grow into them. The mesenteries lose their attach-
ment to the body wall and are probably converted into phacellae.

Fia, 10. Fic. 11.

9.—Surface view of the subumbral or oral aspect of Aurelia aurita, to show the
position of the openings of the subgenital pits, GP. In the centre is the mouth, with four
perradial arms corresponding to its angles, or. The four subgenital pits are seen to be inter-
radial, x, indicates the outline of the roof (aboral limit) of a subgenital pit ; y, the outline of
its floor or oral limit, in which is the opening; 7c, tentaculocyst. (After Lankester.)

10.—Tentaculocyst of Aurelia aurita from the oral aspect. CC, circular canal; H, the
aboral hood; L, the protective lateral lappets ; 7, tentacles; 7’, tentaculocyst, carrying an
ocellus, and a terminal mass of otoliths; 70, endodermal canal of the tentaculocyst; V, the
‘*velarium,” or thin edge of the bell. The outline of the endodermal canals is dotted.

11.—'Tentaculocyst of Aurelia aurita (longitudinal section). A, superior or aboral
olfactory pit; B, inferior or adoral olfactory pit; H, bridge between the two marginal lappets ;
T, tentaculocyst ; nd, endoderm; Ent, endodermal canal continued into the tentaculocyst ;
Con, endodermal concretion (auditory); oc, ectodermal pigment (ocellus), The drawing repre-
sents a section, taken in a radial vertical plane so as to pass through the long axis of the ten-
taculocyst. (After Eimer.)

Concrescence of thes exumbral and subumbral endoderm of the
coelenteron into a gastral lamella ultimately gives rise to the com-
plicated system of gastric pouches and canals of the adult.

:

THE SCYPHOMEDUSAE 71

DESCRIPTION OF THE MeEDusoID.—The umbrella is generally
more or less flattened, and frequently exhibits externally a coronary
furrow which marks off the lappets near the edge of the bell. The
exumbrella is often variously marked by aggregations of pigment
cells and nematocysts. Throughout the group are recognisable in
connection with the edge of the bell, or just above it on the ex-
umbral surface, at least eight tentaculocysts and sixteen marginal
lappets, inherited from the Ephyra.

The tentaculocysts (Figs. 10, 11) rarely exceed eight in number,
but twelve (Polyclonia) or even sixteen or thirty-two may occur.
They lie in incisions at the edge of the umbrella between two lappets,

_ which are, or are parts of, the guard lappets of the eight-rayed

Ephyra ; they are often protected on the exumbral aspect by the
development of a guard plate (Nausithoe). Each consists of a
short stalk, the base of the Ephyra tentacle, with a terminal endo-
dermal mass of crystalline otoliths, covered externally by ecto-
dermal sense cells with long sense hairs; on the exumbral aspect
and proximal end of the stalk lies an ectodermal ocellus. Near
the base of the oral aspect of the stalk lies an ectodermal sense pit,
and a second sense pit is placed above the whole structure on the
exumbral surface of the guard plate.

In addition to the sixteen marginal lappets of the Ephyra,
which lie at the sides of and protect the tentaculocysts, the filling
up of the eight adradial spaces between the eight primary Ephyra-
lobes results in the production of at least eight secondary marginal
lappets, which by fission and intercalation may be very largely
increased in number. '

The tentacles vary considerably in the different sub-orders. In
the Cannostomae they are short and solid; in the Semostomae
they are long and hollow; they are absent in the Rhizostomae.
They may be eight (Pelagia), twenty-four (Chrysaora), or even
more numerous (Cyanea).

The subumbral cavity is generally shallow, and no true velum is
developed ; although the edge of the bell may in a few instances
form a thin velariwm (Aurelia), it bears a different relation to the
nervous system, and is never inflected inwards. The subumbral
surface is in most cases perforated by the openings of the four
subgenital pits. These are chambers (Fig. 9) excavated in the
thickness of the subumbral wall, lined by ectoderm, and lying
interradially immediately under the generative organs, but not
communicating with the coelenteron ; they correspond to, and are
perhaps in some cases formed directly from, the subumbral funnels
of the Scyphistoma, In a few forms all four pits become confluent
centrally, the four openings persisting (Cannorhiza, Figs. 12, 13).
The manubrium is well developed, but assumes different forms in the
different sub-orders ; in Cannostomae it is a simple tube, crucial in

¥

72 THE SCYPHOMEDUSAE

section, with perradial angles, and in some cases provided with
short perradial lappets (Palephyra). In the Semostomae these
lappets are drawn out into long perradial oral arms (Aurelia) with
a median groove, often guarded by frilled edges (Pelagia); the
arms may take origin almost directly from the subumbrella, or
may spring from a fairly long manubrium. Very rarely each arm
bifurcates once (Aurosa). In both these sub-orders a crucial

Fic. 12.

Diagram of Ca t from the subumbral

rl aspect, the arm disc with the eight ora
having been removed, (From Haeckel.)

mouth is placed in the centre of the manubrium between the bases
of the arms.. In the Rhizostomae, a Semostoman stage apparently
occurs in the development, and is followed by an incomplete con-
crescence of the frilled edges of the bifurcated arms over the
median groove and the mouth; thus, instead of a central mouth,
numerous small suctorial openings, numbering often hundreds, are
formed along the edges of the arm, which open by short tubes into

THE SCYPHOMEDUSAE 7

eight brachial canals, the grooves of Semostomae (Fig. 13); these
canals unite into a manubrial cavity, which may either open
directly into the gastric cavity (Rhizostoma), or, owing to the
encroachment of the subgenital pits and the diagonal fusion
across its opening of the four strong pillars which support the
bases of the arms, may communicate with the gastric cavity only
by four perradial pillar canals (Cannorhiza, Figs. 12, 13).

The gastric cavity of the Discomedusae is generally broad and

at Sad .
4

eo3 PS

y

Ty, @
zal
3
i

7
Ma
wy
mee

wie

Diagram of a longitudinal section of Cannorhiza.

Lettering for both figures: ab, perradial arm pillar in Fig. 12, adradial arm in Fig. 13; ah,
mass of tissue formed by the concrescence of the arm pillars ; an, suctorial mouths along the
“oral” faces of the arms; ap, perradial arm pillar; cb, brachial canal, formed by concrescence
of its lips over the brachial groove of Semostomae ; ce, circular canal; cd, arm-pillar canal ;
ci, interradial canal; ep, perradial canal; ga, chamber formed by the union of the brachial
canals—the site of the mouth of Semostomae is immediately under the end of the reference line ;
gc, gastric cavity, cut off from ga by the encroachment of the four subgenital pits and their
union into the subgenital porticus ; gg, gh, gastro-genital membrane, composed above of endo-
derm lining the gastric cavity and forming the generative organs, below of ectoderm lining the
subgenital porticus, with mesogloea between the two; iv, the subgenital porticus=the centrally
confluent subgenital pits, lined by ectoderm; oi, interradial, and op, perradial, otocysts ;
s, endodermal generative organs on floor of gastric cavity ; wm, margin of umbrella. (Fron

Haeckel.)

shallow, and exhibits four interradial pouches, separated by the

four perradial arm pillars, strong ridges of thick mesogloea which

are continued into and support the arms. From these four
19

74 THE SCYPHOMEDUSAE

pouches run the radial canals, the arrangement of which falls
under two main types. In the one type sixteen very broad and
shallow pouches (perradial, interradial, and adradial) pass to the
edge of the bell and end blindly (Pelagia); each may bifurcate,
and may give off short caeca, which never anastomose. In the
second type narrow canals are formed, primarily to the number of
sixteen, which may remain simple (Floscula) or branch (Aurelia)
and anastomose (Leptobrachia): the number of canals may

| Fia. 14.—a, Rhizostoma pulmo ; b, Chrysaora hyoscella. (From Lankester.)

amount to thirty-two or sixty-four. In this second type the
radial canals open into a circular canal. As in the Hydromedusae,
the whole system of radial canals and pouches is produced by a
concrescence of exumbral and subumbral endoderm, traces of which
generally persist throughout life as an endoderm lamella.

The phacellae are of the usual character, and interradially
placed ; they may be only four in number, but are generally very
numerous.

The generative organs are typically four in number and inter-
radial in position, and are formed from the subumbral endoderm
either of the gastric cavity or of the radial pouches. In some
Cannostomae they become secondarily divided so as to form eight
adradial organs (Nausicaa). They are primitively horseshoe-shaped
thickenings of the endoderm, either convex centrally (Palephyra),
or concave centrally (Aurelia) ; they may become folded (Pelagia),
or thrown into lappets (Chrysaora), and may either be evaginated

¢

ieceticccatt rn

THE SCYPHOMEDUSAE 75

as pouches which project on the subumbral surface into the
subumbral cavity (Cyanea), or hang freely into the gastric
cavity or radial pouches (Rhizostoma). The sexes are separate,
except in Chrysaora ; in this genus some individuals are first male,
then hermaphrodite, and finally female only, the ova being con-
fined to the interradial generative organs, the spermatozoa occur-
ring irregularly at any point in the endoderm; other individuals
are unisexual throughout life.

CLASSIFICATION AND LIST OF GENERA OF
SCYPHOMEDUSAE.

The chief authority for this classification is Haeckel (6) ; other attempts
are to be found in Claus, Veber die Classification der Medusen (Arb. Zool.
Inst. Wien, vii. 1888), and Vanhéffen, Zur System der Scyphomedusen (Zool.
‘Anz. xiv. 1891).

OrpER 1. Stauromedusae. (For definition, see p. 61.)

Famity 1. TessermDArE. Genera—Tessera, Hkl.; Tesserantha, Hkl. ;
Depastrella, Hkl.; Depastrum, Gosse; Tesseraria, Hkl.. Famity 2.
LUCERNARIIDAE. Genera—Haliclystus, Clark ; Lucernaria, O. F. Mill. ;
Halicyathus, Clark ; Craterolophus, Clark ; Lucernosa, Antipa. Famity 3.
CAPRIIDAE. Geos — 0s apria, Antipa.

ORDER 2. Peromedusae. (For definition, see p. 63.)

Famity 1. Pertcorprpar. Genera—Pericolpa, Hkl. ; Pericrypta, Hk1.
Faminy 2. PERIPHYLLIDAE. Genera— Peripalma, Hkl.; Pertphylla,
Steenstr. ; Periphema, Hk.

¢
OrvDER 3. Cubomedusae. (For definition, see p. 64.)

Famity 1. CHARYBDEIDAE. Genera — Procharagma, Hkl.; Pro-
charybdis, Hkl.; Charybdaea, Pér. Les.; Tamoya, F. Mill. Famrity 2.
CHIRODROPIDAE. Genera—Chiropsalmus, L. Agass.; Chirodropus, Hk.

OrvER 4. Discomedusae. (For definition, see p. 67.)
Sus-ORDER 1. CANNOSTOMAE.

Definition—The mouth is simple and devoid of arms. The ten-
tacles are solid and generally short.
Famity 1. EpHYRIDAE (in many cases probably larval forms). Genera
» —ELphyra, Pér. Les. ; Palephyra, Hkl.; Zonephyra, Hkl.; Nausicaa, Hk. ;
Nausithoe, Koll.; Nauphanta, Hkl.; Atolla, Hkl.; Collaspis, Hkl.
Famiry 2. Linercipar. Genera — Linerges, Hkl.; Linantha, Hk. ;
Liniscus, Hkl.; Linuche, Esch.

.

76 LITERATURE OF THE SCYPHOMEDUSAE

Sus-OrRDER 2. SEMOSTOMAE.

Definition —The mouth is provided with four oral arms. The ten-
tacles are hollow, and generally long.

Famity 3. PELAGIpAE. Genera—Pelagia, Pér. Les.; Chrysaora, Pér.
Les. ; Dactylometra, L. Agass. Famity 4. CYANEIDAE. Genera— Pro-
cyanea, Hkl.; Medora, Couthouy ; Stenoptycha, L. Agass. ; Desmonema, L.
Agass.; Drymonema, Hkl.; Cyanea, Pér. Les.; Patera, Less.; Melusina,
Hk. Faminy 5. Fioscuntmpar. Genera—Floscula, Hkl; Floresca, Hk1.
Famity 6. ULMARIDAE. Genera—Ul/maris, Hkl.; Umbrosa, Hkl.; Undosa,
HklL; Sthenonia, Esch.; Phacellophora, Brandt; Aurelia, Pér. Les. ;
Aurosa, Hkl.; Awricoma, Hkl.

Sus-OrDER 3. RHIZOSTOMAE.

Definition —The mouth is obliterated by the central fusion of the
four bifurcated oral arms, and is functionally replaced by numerous suck-
ing mouths on their “oral” aspect ; tentacles are absent.

FamIty 7. TOREUMIDAE. Genera—Archirhiza, Hkl.; Torewma, Hk1. ;
Polyclonia, L. Agass.; Cassiopeja, Pér. Les.; Cephea, Pér. Les. ; Polyrhiza,
L. Agass. Famity 8. Prnemmpar. Genera—Tozoclytus, L. Agass. ; Lych-
norhiza, Hkl.; Phyllorhiza, L. Agass.; Eupilema, Hkl.; Pilema, Hk1. ;
Rhopilema, Hk. ; Brachiolophus, Hkl.; Stomolophus, L. Agass.; Necto-
pilema, Fewk. Famity 9. VersurmDaE. Genera—Haplorhiza, HkL ;
Cannorhiza, Hkl.; Versura, Hkl.; Crossostoma, L. Agass.; Cotylorhiza,
L. Agass.; Stylorhiza, Hkl.; Loborhiza, Vanhéffen. Famiy 10. Cram-
BESSIDAE. Genera—Crambessa, Hkl.; Mastigias, L. Agass. ; Eucrambessa,
HkL; Thysanostoma, L. Agass.; Himantostoma, L. Agass.; Leptobrachia,
Brandt ; Leonura, Hkl.; Cramborhiza, Hk.

LITERATURE OF SCYPHOMEDUSAE.

1. Clark. (Lucernariae and their Allies.) Smithsonian Contrib. to Know-
ledge, 242. 1878.

Claus. (Studien. ii. Polypen u. Quallen der Adria.) Denkschr. Akad.
Wien, 1877.

8

3. Ibid. (Unters. ii. Charybdea marsupialis.) Arb. Zool. Inst. Wien, 1878.

4. Ibid. Unters. ti. d. Organis. u. Entwickl. d. Medusen, 1883.

5. Ibid. (Entwickl. d. Seyphostoma.) Arb. Zool. Inst. Wien, ix., x., 1891-93.
6. Haeckel. System der Medusen, 1879-80.

7. Ibid. (Deep Sea Medusae.) Chall. Rep. Zool. iv., 1882.

8. Hertwig. (Organismus der Medusen.) Denkschr. Ges. Jena, ii., 1878.

9. Ibid. Nervensystem und Sinnesorgane der Medusen, 1878.

10. Hesse. (Nervensyst. u. Sinnesorgane von Rhizostoma.) Zeit. wiss. Zool.

Ix., 1895.

11. Jackson. Forms of Animal Life, pp. 780-790, 1888.

12. Lankester. Encyclopaedia Britannica, ed. ix., Article Hydrozoa, 1881.

13. Schewiakof. (Beitr. z. Kenntniss d. Acalephenauges.) Morph. Jahrb. xv.,
1889.

tea es Am,

INDEX

To names of Classes, Orders, Sub-Orders, and Genera ; and to technical terms.

Abyla, 56
Acanthella, 55
Acanthocladium, 29, 54
Acaulis, 53
Acharadria, 53
acrocyst, 28, 45
Actinogonium, 53
actinula larva, 22
adradial canals, 6
adradii, 4 (Fig. 7)
Aegina, 55
Aeginella, 33, 55
Aegineta, 33, 55
Aeginidae, 55
Aeginodiscus, 55
Aeginodorus, 55
Aeginopsis, 35, 55
Aeginorhodus, 55
Aeginura, 34, 55
Aequorea, 24, 54
Aequoridae, 54
Agalma, 47, 56
Agalmidae, 56 ¥
Agalmopsis, 39, 40, 56
Aglaisia, 56
Aglantha, 30, 32, 55
Aglaophenia, 23-25 (Fig.
31), 27, 28 (Fig. 37),
29, 54
Aglaopheniidae, 54
Aglaura, 32, 55
Aglauridae, 55
Aglauropsis, 55
Agliscra, 55
Allopora, 35-37 (Fig. 43a),
388, 55
Alophota, 57
alternation of generations,
18
Amalthaea, 16, 52
Ametrangia, 54
Amphicaryon, 56
Amphicodon, 52
Amphinema, 52
Amphirrhoa, 56

ampullae (medusoid), 36,
38

Angela, 57

Angelopsis, 57

Anisicola, 23

Antennularia, 55

Anthemodes, 56

Anthomedusae, 11-22, 52

Anthophysa, 56

Anthophysidae, 56

Apolemia, 39, 45, 56

Apolemiidae, 56

Apolemopsis, 56

Archirhiza, 76

Arethusa, 57

Armenista, 56

Astylus, 37, 38 (Fig. 43a),
f 5D

Athoralia, 56

Athoria, 40, 45, 56

Athoriidae, 56

Athorybia, 56

Atolla, 75

Atractylis, 53

Auralia, 57

Aurelia, 6 (Fig. 7bis), 9
(Fig. 10), 61, 67, 70, 76

Auricoma, 76

Auronectae, 56

aurophore, 42

Aurophysa, 57

Aurosa, 72, 76

Azygoplon, 54

Bassia, 56
Bathycodon, 52
Bathyphysa, 56
Berenice, 26, 54
Bimeria, 53
blastocoele, 22
blastostyle, 14
blastula, 2, 22
Bougainvillea, 11-14 (Fig.
19), 16-19, 20, 53
Bongainvillidae, 53

brachial canal, 73
Brachiolophus, 76

bract, 40

budding of hydroid, 3, 4
— of medusoid, 17-19

Calamphora, 54

Calicarpa, 55

Calicarpidae, 55

Callitiara, 16, 52

Calpe, 56

Calycella, 23, 28, 54

Calyconectae, 56

Calyptoblastea, 53

Campaniclava, 53

Campanopsis, 23

Campanularia, 23, 27, 29,
54

Campanularidae, 54

Campanulina, 26, 27, 54

Cannophysa, 57

Cannorhiza, 71-73, 76

Cannostomae, 75

Cannota, 54

Cannotidae, 54

Capria, 75

Capriidae, 75

Caravella, 57

Carmarina.

Carmaris, 55

Cassiopeja, 76

Catablema, 52

centradenia, 42

centripetal canals, 32

Cephea, 76

Ceratella, 13, 53

Ceratelladae, 53

Charybdaea, 61, 65, 66, 75

Charybdeidae, 75

Chirodropidae, 75

Chirodropus, 65, 66, 75

Chiropsalmus, 75 :

Chrysaora, 67 (Fig. 6), 68,
71, 74 (Fig. 146), 75, 76

Cionistes, 53

See Geryonia

78 INDEX TO HYDROMEDUSAE & SCYPHOMEDUSAE
eee

Circalia, 56
Circaliidae, 56
circular canal, 5
cirrhi, 24
Cladocanna, 54
Cladocarpus, 54
Cladocoryne, 11, 53
Cladocorynidae, 53
Cladonema, 17, 19, 53
Cladonemidae, 53
Clathrozoon, 23, 55

Clava, 15 (Fig. 21), 20, 53

Clavatella, 16, 17, 19, 53
Clavatellidae, 53
Clavidae, 53
Clavula, 53

Clytia, 23, 54
cnidoblasts, 6
enidocil, 6
cnidophore, 16
Codonidae, 52
Codonium, 17, 52
Codonorchis, 52
coelenteron, 2
coenenchyme, 35
coenosare, 4
coenosteum, 35
Collaspis, 75
colletocystophore, 62
colony formation, 4
Conis, 52
Conopora, 55
Coppinia, 27, 55
corbula, 29

Cordylophora, 13, 18 (Fig.

29), 20, 53
cordylus, 9
cormidium, 45
Corydendrium, 13, 53

Corymorpha, 12, 15 (Fig.

23), 16, 53
Corymorphidae, 53
Coryne, 11, 13, 20, 21, 53
Corynetes, 52, 53
Corynidae, 53
Corynopsis, 53
Cotylorhiza, 76
Crambessa, 76
Crambessidae, 76
Cramborhiza, 76
Craterolophus, 75
Crossostoma, 76
Cryptohelia, 36, 55
Cryptolaria, 54
Ctenaria, 18 (Fig. 26), 53
Cubogaster, 52
Cuboides, 56
Cubomedusae, 64, 75
Cucubalus, 56
Cucullus, 56
Cunantha, 33, 34

Cunanthidae, 55
Cunarcha, 55
Cuneolaria, 56

Cunina, 7 (Fig. 10), 11, 34,

35, 55
Cunissa, 55
Cunoctantha, 35, 55
Cunoctona, 55
Cupulita, 56
Cuspidella, 54
Cyanea, 71, 75, 76
Cyaneidae, 76
cyclosystem, 36
Cymba, 56
Cymbonectes, 42, 56
Cystalia, 57
Cystaliidae, 57
cyston, 45
Cystonectae, 57
Cytaeis, 52
Cytandraea, 52

Dactylometra, 76
dactylopore, 35
dactylozooid, 16
Dawsonia, 50
Dehitella, 53
Dendroclava, 53
Dendrograptus, 50
Dendroidea, 50
Dendronema, 53
Depastrella, 75
Depastrum, 75
Desmalia, 56
Desmonema, 76
Desmophyes, 56
Desmophyidae, 56
Desmoscyphus, 54

diblastula, 2, 22, 60 (Fig. 1)

Dichograptidae, 50
Dicodonium, 52
Dicoryne, 21, 22, 53
Dicranocranna, 54
Dicranograptidae, 50
Dictyocladium, 54
Dictyonema, 50
Dicymba, 56
digestive cells, 7
Dimorphograptus, 50
Dinema, 52
Dipetasus, 55
Diphasia, 28, 24, 30, 54
Diphyes, 40, 42, 56
Diphyidae, 56
Diphyopsis, 56
Dipleurosoma, 54
Diplocheilus, 54
Diplocyathus, 54
Diplograptidae, 50
Diplophysa, 56
Diplura, 52

Diprionidae, 50
Dipurena, 52
Discalia, 55
Discalidae, 55
Discolabe, 56
Discolabidae, 56
Discomedusae, 67, 75
Disconalia, 55
Disconectae, 55
Dissonema, 24, 53
Distichopora, 35, 36, 38, 55
Doramasia, 56
Drymonema, 76
Dyscannota, 54
Dysmorphosa, 52

ectoderm, 2

— of hydroid, 6, 7

— of medusoid, 8

Ectopleura, 52, 53

Eleutheria, 17, 53

endoderm, 2

— of hydroid, 7, 8

— of medusoid, 11

— lamella, 5

entocodon, 18

Epenthesis, 54

Ephyra, 68, 70, 75

Ephyridae, 75

Epibulia, 47, 57

Epibulidae, 57

epithelio-muscular cells, 6

Errina, 37 (Fig. 43a), 55

Ersaea, 56

Ersaeidae, 56

Ersaeome, 41 (Fig. 47), 45

Euchilota, 10 (Fig. 13), 54

Eucope, 24, 26, 54

Eucopidae, 54

Eucopium, 54

Eucrambessa, 76

Eudendriidae, 53

Eudendrium, 11, 13, 14, 16,
18 (Fig. 28), 20-22, 53

Eudoxella, 56

Eudoxidae, 56

Eudoxome, 45

Euphysa, 16, 52

Eupilema, 76

Eutima, 54

Eutimalphes, 54

Eutimeta, 54

Eutimium, 54

exumbral (adj.), 5

false blastostyle, 14
festoon canal, 34

Filellum, 54

fission, in hydroids, 21, 30
— in medusoids, 30

a
j

INDEX TO HYDROMEDUSAE & SCYPHOMEDUSAE 79

Floresca, 76 Hebella, 54 Lilyopsis, 56
Floscula, 74, 76 Heterocordyle, 53 Limnocea, 52
_ Flosculidae, 76 Heteroplon, 55 Limnoenida, 47-49
Forskilea, 39, 40, 45, 56 Heterostephanus, 53 Limnocodium, 47-49
Forskalidae, 56 Himantostoma, 76 Linantha, 75
Forskéliopsis, 56 Hippocrene, 52 Linerges, 75
frenula, 65 Hippopodius, 56 Linergidae, 75
Hippurella, 55 Liniscus, 75
Galeolaria, 45, 56 Homoeonema, 55 Linophysa, 57
ganglion cells, 7 Hybocodon, 52 Linuche, 75
Garveia, 53 Hydra, 2, 3, 11-13, 20, 22, | Liriantha, 55
gastral lamella, 5 53 Liriope, 30, 32, 55
gastric cavity, 5 Hydractinia, 13, 14, 15 | Lizusa, 52
gastropore, 35 (Fig. 22), 16, 21, 53 Lizzella, 52
gastrozooid, 36 Hydractiniidae, 53 Lizzia, 10 (Fig. 11), 16, 52
gastrula, 2, 22 Hydrallmania, 54 Loborhiza, 76
Gemmaria, 53 hydranth, 2 Lovénella, 54
gemmation. See budding | Hydranthea, 53 Lucernaria, 62, 75
generative cells, 11 Hydrella, 54 Lucernariidae, 75
— origin and migration in | Hydridae, 53 Lucernosa, 75
Hydromedusae, 20, 21 hydrocaulus, 5 Lychnagalma, 56
— in Leptomedusae, 29 Hydroceratinidae, 55 Lychnorhiza, 76
Geryones, 31, 55 hydrocladia, 23 Lytocarpus, 29, 54
Geryonia, 30-33, 35, 55 Hydrocorallinae, 35-38, 55 | Lytoscyphus, 54
Geryonidae, 55 hydrocyst, 39
Globiceps, 52 hydroecium, 42 machopolyps, 24
Glossocodon, 55 hydroid, 2-5 manubrium, 5
Glossoconus, 55 — histology, 6-8 Margelidae, 52
gonodendron, 40 Hydrolaridae, 53 Margelis, 52
gonophore, 5 hydrotheea, 5 Margellium, 52
gonostyle, 40 Hydromedusae, 1 marginal cirrhi, 24
gonotheca, 6, 27 hydrophyllium, 40 — funnels, 26
Gonothyraea, 27, 29, 54 hydrorhiza, 5 — tubercles, 25
gonozooid, 5 Hydrozoa, 1 Marmanema, 32, 55
Gononema, 54 Hypanthea, 54 marsupium, 28
\ Gossea, 55 Hypopyxis, 54 Mastigias, 76
Grammaria, 54 Hypostome, 3 meconidium, 28
Grammariidae, 54 Medora, 76
Graptolithidae, 50, 51 Idia, 54 medusoid, 5
Graptoloidea, 50 Idiidae, 54 — histology of, 8-11
gubernaculum, 27, 30 infundibulum, 42 Melicertella, 54
Gymnoblastea, 52 interradial canals, 6 Melicertidium, 54
Gymnocoryne, 53 interradii, 4 (Fig. 7) Melicertissa, 54
| interstitial cells, 7 Melicertum, 26, 54
Halatractus, 53 involucrum, 39 Melophysa, 56
Haleciidae, 54 Trene, 25 (Fig. 33), 54 Melusina, 76
Halecium, 23, 37, 54 Trenium, 54 Merona, 53
Haleremita, 53 mesentery, 61
Haliclystus, 61-64 (Fig. 3), | Labiopora, 55 mesogloea, 2
75 ; Lafoea, 23, 54 — of hydroid, 8
Halicornaria, 54 Laodice, 24, 54 — of medusoid, 11
' Halicornariidae, 54 Laomedea, 27, 54 mesogonium, 32
' Halicyathus, 75 Lar, 16, 17, 58, 54 Mesonema, 54
: Halisiphonia, 54 lens, 9 metagenesis, 18
Halistemma, 47, 56 Leonura, 76 Microhydra, 11, 49, 53
Halmomises, 54 Leptobrachia, 74, 76 Millepora, 35-38, 55
» Halocordyle, 53 Leptograptidae, 50 Milleporidae, 55
Haloikema, 54 Leptomedusae, 22-30, 53 Mitrocoma, 22, 54
THalopsis, 54 Leptoscyphus, 54 Mitrocomella, 54
Halopyramis, 56 Lictorella, 54 Mitrocomium, 54

Haplorhiza, 76 Lilaea, 56 Mitrophyes, 56

80 INDEX TO HYDROMEDUSAE & SCYPHOMEDUSAE

Modeeria, 52
Monobrachiidae, 53
Monobrachium, 53
Monocaulidae, 53
Monocaulus, 53
Monogastricae, 56
Monograptidae, 50
Monophyes, 56
Monophyidae, 56
Monoprionidae, 50
monosiphonie (adj.), 23
Muggiaea, 56
Myrionema, 53
Myrionemidae, 53
Myriothela, 11, 22, 53
Myriothelidae, 53

Narcomedusae, 33-35, 55
Nauphanta, 75
Nausicaa, 74, 75
Nausithoe, 71, 75
Nectalia, 56
Nectalidae, 56
nectocalyx, 40
nectophore, 40
Nectophysa, 57
Nectopilema, 76
nectozooid, 40
nematocyst, 6
nematophores, 24
Nemertesia, 55
Nemopsis, 17, 52

Obelaria, 54

Obelia, 23-25 (Fig. 32),
26-28 (Fig. 35), 29, 54

ocellus, 9

Octocanna, 54

Octonema, 53

Octorchandra, 54

Octorchidium, 54

Octorchis, 26, 54

oleoeyst, 45

Olindias, 31, 32, 55

Opercularella, 54

Ophiodes, 24, 54

Orchistoma, 26, 54

otocyst, 9

otolith, 9

otoporpae, 34

Palephyra, 72, 74, 75

Patera, 76
Pectanthis, 30, 31, 55
Pectis, 55

Pectyllis, 55

pedalia, 63
Pegantha, 55
Peganthidae, 55
Pegasia, 55
Pelagia, 71, 72, 74, 76
Pelagidae, 76
Pennaria, 53
Pennariidae, 53
Pericolpa, 64, 75
Pericolpidae, 75
Pericrypta, 75
Perigonimus, 12, 13, 15
(Fig. 20), 16, 17, 53
Peripalma, 75
Periphema, 75
Periphylla, 64, 75
Periphyllidae, 75
perisare, 5
Perisiphonia, 54
Perisiphoniidae, 54
Peromedusae, 63, 75
peronia, 31, 34
perradial canals, 6
perradii, 64 (Fig. 7)
Persa, 55
Petachnum, 55
Petasata, 55
Petasidae, 55
Petasus, 32, 55
phacella, 61
Phacellophora, 76
Phialidium, 10 (Fig. 12), 54
Phialis, 54
Phialum, 54
phylactocarp, 29
phyllocyst, 40
Phyllograptidae, 50
Phyllophysa, 56
Phyllorhiza, 76
phyllozooid, 40
Physalia, 40, 45, 46 (Pigs.
49, 51), 57
Physaliidae, 57
Physonectae, 56
Physophora (Fig. 45), 41,
56

Pilema, 76

Pilemidae, 76

pillar canal, 73

pinnae, 23

pistillum, 42

planula, 22

Pleurophysa, 57

Pliobothrus, 55

Plumularia, 23, 24, 27, 55

Plumulariidae, 55

pneumatophore, 40

Pneumophysa, 57

Podocoryne, 12, 14, 16, 21,
53

Podocorynidae, 53

Polycanna, 24, 26, 54

Polyclonia, 71, 76

Polycolpa, 55

polymorphism, Antho-
medusae, 14-16, 20, 21

— Leptomedusae, 24, 26-
29

Polyorchis, 54

Polyphyes, 56
Polyphyidae, 56

polypite, 39
Polyplumaria, 55
Polypodium, 21
Polyrhiza, 76
polysiphonic (adj.), 23
Polyxenia, 55

Porpalia, 56

Porpema, 56

Porpita, 43 (Fig. 48a), 56
Porpitella, 56

Porpitidae, 56

Praya, 45, 56
Proboscidactyla, 54
Procharagma, 65, 75
Procharybdis, 65, 75
Procyanea, 76

Protiara, 52

Protohydra, 21, 49, 53 ;
pseudo-manubrium, 31
Pteronema, 53

Pterophysa, 57 t
Ptychogena, 54 ~

radii, 4 (Fig. 7)

rami, 23

ramuli, 23 ;
Rataria, 56
Rathkea, 52 ;
Retioloidea, 51
Rhegmatodes, 54

Rhizogeton, 53

Rhizophysa, 45, 57
Rhizophysidae, 57

Rhizostoma, 74 (Fig. 14a)

75 ;
Rhizostomae, 76
Rhodalia, 57
Rhodaliidae, 57
Rhodophysa, 56
gr ew 10 (Fig. 14),

11, 32, 5
Rhopilema, "6

Salacia, 54, 57
Salaciidae, 57
Saphenella, 54

Saphenia, 54

Sarsia, 16, 17 (Fig. 25), 52
Schizocladium, 30
Schizotricha, 55

—_—

INDEX TO HYDROMEDUSAE & SCYPHOMEDUSAE 81

Sciurella, 55
scyphistoma, 61, 68
Scyphomedusae, 60-76
Scyphozoa, 1
seyphula, 68
Semostomae, 76

sense cells, 6

— organs, 9-11
Sertularella, 27, 29, 54

' Sertularia, 27, 28 (Fig. 36),

54
Sertulariidae, 54
sicula, 50
siphon (siphonophora), 39
Siphonophora, 38-47, 55
Slabberia, 52
Sminthonema, 31
Solmaridae, 55
Solmaris, 33, 35, 55
Solmissus, 55
Solmoneta, 55
Solmundella, 55
Solmundus, 55
somatocyst, 45
spadix, 20
Sphaerocoryne, 53
Sphaeronectes, 56
Sphenoides, 56
Sphyrophysa, 56
Spinipora, 35, 87, 55
Spongicola, 53
Spongicolidae, 53
Sporadopora (Fig. 43d), 38,

55

sporosac, 20
Stawraglaura, 55
Stauridium, 53
Staurobrachium, 54
Staurodiscus, 26, 54
Stauromedusae, 61, 68, 75
Staurophora, 54
Staurostoma, 24, 54
Stawrotheca, 54
Steenstrupia, 52
Stenohelia, 55
Stenoptycha, 76
Stephalia, 45, 57
Stephalidae, 57
Stephanomia, 56
Stephanophyes, 56

Stephanophyidae, 56
Stephanoscyphus, 53
Stephanospira, 56
Stephonalia, 57
Sthenonia, 76
Stomobrachium, 54
Stomolophus, 76
Stomotoca, 52
Streptocaulus, 54
Strobalia, 56
Stylactella, 53
Stylactis, 53
Stylaster, 35-37, 55
Stylasteridae, 55
style (calcareous), 36
Stylorhiza, 76
subgenital pit, 61, 71
subumbral (adj.), 5
— funnel, 61

— papillae, 26
Syncoryne, 17, 53
Syndictyon, 52
Synthecidae, 54
Synthecium, 54

tabulae, 36
taeniolae, 61
Tamoya, 75
tentacle, 3
tentaculocyst, 9, 70 (Figs.
LO5-L0); 71
tentillum, 39
Tessera, 61-63, 75
Tesserantha, 62, 75
Tesseraria, 75
Tesseridae, 75
Tetranema, 53
Tetraplatia, 49
Tetrapteron, 49
Thamnitis, 52
Thamnostoma, 52
Thamnostylus, 52
Thaumantias, 30, 58, 54
Thaumantidae, 53
Thecocladium, 54
Thuiaria, 54
Thyroscyphus, 54
Thysanostoma, 76
Tiara, 16, 52
Tiarella, 53

Tiaridae, 52

Tiaropsis, 54

Tima, 54

Toreuma, 76

Toreumidae, 76

Toxoclytus, 76

Toxorchis, 54

tracheae, 42

Trachomedusae, 30-33, 55

Trachynema, 33, 55

Trachynemidae, 55

Trichydra, 55

trophozooid, 2

Tubiclava, 53

Tubularia, 11, 14, 16 (Fig.
24), 17, 20, 22, 58

Tubulariidae, 53

Turridae, 53

Turris, 52, 53

Turritopsis, 35, 52

Ulmaridae, 76
Ulinaris, 76
Umbrella, 5
Ummbrosa, 76
Undosa, 76

velarium, 61

Velella, 39, 40, 42, 43 (Fig.
48a), 46 (Fig. 50), 56

Velellidae, 56

velum, 5

Versura, 76

Versuridae, 76

virgula, 50

Vogtia, 56

Vorticlava, 53

Willetta, 54
Willsia. See Lar
Wrightia, 53

Zanclea, 53
Zonephyra, 75
Zygocanna, 54
Zygocannota, 54
| Zygocannula, 54
| Zygodactyla, 54

CHAPTER VI.

THE ANTHOZOA.!

CLASS ANTHOZOA.
Sup-CLass 1. ALCYONARIA.

GRADE A. PROTALCYONACEA (no Orders).
GRADE B. SYNALCYONACEA.
Order 1. Stolonifera.

2. Alcyonacea.

3. Pseudaxonia.

» 4. Axifera.
5. Stelechotokea.
6. Coenothecalia.

SuB-CLass 2. ZOANTHARIA.
GRADE A. PARAMERA.

Order 1. Cerianthidea.
, 2. Antipathidea.

» 3. Zoanthidea.
4. Edwardsiidea.

5, 0. Proactiniae.

GRADE B. CryPpTOPARAMERA.
Order 6. Actiniidea.
Sub-Order 1. Malacactiniae.
FS 2. Scleractiniae (= Madreporaria).
Section 1. Aporosa.
» 2. Fungacea.
‘“d 3. Perforata.

THE animals which we now class together as Anthozoa have
been familiar to naturalists from the days of antiquity, but our
knowledge of their true nature and affinities is of comparatively
recent date. To this day we are far from being able to give a
satisfactory account of the relationships of the different groups
comprised in the class,

1 By G. C. Bourne, M.A.

2 THE ANTHOZOA

To the earliest authors of antiquity the larger and more strik-
ing members of the Anthozoa were partly animal, partly vegetable
productions, and hence they were known as zoophytes ((w6¢vra),
a name which is still in popular use. But many of the Anthozoa,
particularly those which have conspicuous horny or calcareous
skeletons, were for a long time regarded as mineral products, or
in some cases were fancifully supposed to have the double nature
of plants and minerals. The popular conception of coral was ex-
pressed by Ovid in the fourth book of the Metamorphoses -—

nune quoque coralliis eadem natura remansit ;
duritiam tacto capiant ut ab aere, quodque
vimen in aequore erat, fiat super aequore saxum.

It is true that Aristotle had long before this recognised the
animal nature of the ordinary sea-anemones or Actinians, which he
described sometimes under the name of “Cnidae,” sometimes of
“ Acalephae” ; the Medusae were also included by him under the
same name. Aristotle’s observations on Actinians and Medusae
are given in the sixth chapter of the fourth book of the Historia
animalium, and it was long before any substantial addition was
made to them. Theophrastus, a pupil of Aristotle, regarded the
precious coral of commerce as a mineral which, because of its red
colour, was comparable to haematite ; but the Gorgonians he con-
sidered to be plants. Several of the authors of antiquity fell into
the same error of regarding different forms of Anthozoa as plants ;
and Pliny, who was acquainted with a considerable number of
them, describes some as plants, some as minerals, and others as
occupying an intermediate position between the animal and
vegetable kingdoms. ‘Equidem et his inesse sensum arbitror
quae neque animalium neque fructicum sed tertiam quamdam ex
utroque naturam habent; urticis dico et spongiis” (J/istoria
naturalis, lib. ix. ch. 68).

Amongst the species described by Pliny are several Gorgonians
and two forms which he described as marine plants under the
names of “Isis crinis” and “ Charitoblepharon.” They may have
been Antipatharia or Pennatulids.

From the days of Pliny until the sixteenth century no addition
was made to the knowledge of the Anthozoa. But we find that
the encyclopaedists described and figured Actinians as animals.
Rondelet (1534) and Belon (1551) described them in their works
de piscibus marinis, and their statements were accepted and repeated
by Wotton (1552), Conrad Gesner (de aquatilibus, 1558), Aldrovandus
(Animalia exsanguia, Zoophyta, 1606), and John Johnston (de ez-
sanguibus aquaticis, 1657). But the prevailing error which regarded
the colonial forms as plants, led to the Anthozoa being chiefly
studied by botanists. Lobel, for instance, in 1591 gave drawings

ieee

THE ANTHOZOA 3

of six species which are recognisable as (1) Madrepora oculata ;
(2) Dendrophyllia ramea; (3) Coralliwm rubrum ; (4) Antipathes ;
(5) and (6) Gorgonians.

Theodore Tabernaemontanus extended the error and figured
amongst marine plants, not only the precious red coral and some
Gorgonians, but also an Actinian, thus taking a step backwards
from the position already gained by Aristotle. Similarly we find
Gorgonians and Corals described as plants by Tournefortand Ferrante
Imperato. All these authors seem to have been acquainted only
with the dry condition of Corals and Gorgonians. The first step
in advance was made by Paul Boccone, who, in the seventeenth
century, conceived the idea of accompanying the coral divers on
their expeditions from Messina in order to study corals in the
fresh condition. He showed that the branched axis which forms
the major part of the red coral is covered in the fresh condition
with a soft tissue, and he discerned in this tissue the radiate pores
of the retracted polyps. He combated the view that the coral
was a plant, but fell into the still graver error of explaining their
nature to be thatof a simple stony concretion. Similar investigations
were undertaken at a later date by the Comte de Marsilli, and by
an Englishman named Shaw, both of whom regarded corals as
plants, and their views were adopted in full by the illustrious
Réaumur.

The discovery of the true nature of Corals and Gorgonians is
due to Jean André de Peyssonel, a native of Marseilles, who made
a number of observations on corals on the coast of Barbary, and
kept several forms alive in aquaria. He saw the expanded polyps,
and recognised their true nature, and he made some observations
on their anatomy: “Je fis fleurir le corail dans des vases pleins
d’eau de mer et j’observais que ce que nous croyions étre la fleur
de cette prétendue plante n’était, au vrai, qu'une insecte semblable
& une petite ortie ou poulpe. Cette insecte s’épanouit dans l’eau
et se ferme A lair, ou lorsque je versais des liqueurs acides, ou
que je le touchais avec la main j’avais le plaisir de voir remuer les
pattes ou pieds de cette ortie.” ’

Peyssonel’s observations were laid before the Academy of
Sciences of France in 1727, but his views were strongly opposed by
Réaumur, whose authority was sufficient to condemn them. It was
not till 1751 that they found full expression and acceptance at the
hands of the Royal Society of London, and were fully published
in London under the title of Traduction @un article des Tran-
sactions Philosophiques sur le Corail. In the meantime Trembley
had made his classical researches on Hydra, and had communicated
them to Réaumur, who in company with Bernard de Jussieu
repeated Trembley’s observations, and discovered on the coasts
of Normandy living and expanded Alcyonarians, covered with

5

4 THE ANTHOZOA

multitudes of little polyps like those which Trembley had
described. After this there was no resisting Peyssonel’s opinion,
and the name of polyps was given by Réaumur to the Hydra, to
Corals, and Actinians alike, because of their fancied resemblance to
the “ Poulpe” or Octopus ; because, as he said, “leurs cornes sont
analogues aux bras de l’animal de mer qui est en possession de ce
nom.”

The discovery of the animal nature of corals attracted many
naturalists to the study of the Anthozoa, and considerable
works on the group were published by Ellis (21), Cavolini, and
Esper (Die Pflanzenthiere, Nuremberg, 1791). The works of these
authors contained many errors. No distinction was made between
Hydroid polyps, Polyzoa, Corals, Sponges, and even’ Ascidians.
The separation of the last named was due to Savigny. Neither
Cuvier, Lamarck, or Lamouroux dealt with the anatomy of “polyps,”
but founded their systems on the characters of the skeletons or
polyparies. It was Milne-Edwards who, in conjunction with
Audouin, first demonstrated in 1828 that Flustra and its allies are
distinguished from the Actinians and Coral polyps by the possession
of a separate mouth and anus, and that the sponges form a separate
group characterised by the absence of polyps. In 1830 Vaughan
Thompson, and in 1834 Ehrenberg, finally separated Flustra
and its allies under the names Polyzoa and Bryozoa, but the
Hydrozoa were still confounded with the Anthozoa, and it
required some years of labour on the part of Sars, Dujardin, von
Siebold, P. van Beneden, and Desor in order to effectually separate
the two groups. The anatomy and classification of the group
thus purged of intruders were placed on a firm basis by the
classical works of Dana, and of Milne-Edwards and Haime (1857),
and in more recent years the studies of de Lacaze-Duthiers,
Kowalevsky, G. von Koch, and E. B. Wilson on development, of
A. Agassiz, Moseley, G. von Koch, and others on the comparative
anatomy, and O, and R. Hertwig on the histology of many forms
of Anthozoa have gone far to render our knowledge of the group
more exact, though, as yet, far from complete.

The Anthozoa, whose history has been shortly considered, form
a class of the phylum Coelentera. Leaving the Porifera and
Ctenophora out of consideration, as possessing structural and
embryonic features which separate them somewhat sharply from
the remainder of the Coelentera, the fundamental morphological
concept of a Coelenterate animal is a polyp or zooid.

The term polyp, as has been shown above, is due to a fancied
resemblance between the coelenterate individual and the Poulpe or
Polypus, as the common Octopus was popularly named in France.
In spite of its fanciful origin, the term has come into general use,

ce

THE ANTHOZOA 5

but it is much less convenient for practical purposes than the
term zooid, which is applied to the individuals which compose
colonial organisms in several other groups in the animal kingdom.
There is no inconvenience in applying the same general term to
the individual members of different groups, if it is clearly under-
stood at the outset that there are several kinds of zooids, differing
from one another in important anatomical features, and if we bear
in mind that the term is more particularly applicable to the
asexually produced individuals composing a colony, but may
also be transferred to individuals, similar to the colonial forms in
all respects, except that they do not form colonies. Throughout
this chapter, the term zooid will be employed instead of the older
term polyp, to designate an Anthozoan individual. It is true
that Kélliker has used the term, in a special and limited sense, in
describing certain Anthozoa, but his special use of the term is
unwarrantable, and will be referred to further on.

A Coelenterate zooid is an animal consisting of a hollow sac
of various form—columnar, spherical, or disc shaped. The cavity
of the sac, known as the coelenteron, is the only cavity of the
body, and communicates with the exterior by an opening, the
mouth, which serves the double purpose of admitting food into
the cavity of the sac, and of expelling undigested matter ; and in
the Anthozoa the reproductive elements. There is rarely a second
aperture at the end of the body furthest from the mouth opening.
A vertical line passing through the centre of the mouth is the
principal axis of the coelenterate body, the secondary axes being
disposed radially with regard to the principal axis, though, as will
be seen further on, there are many cases in which the primitive
radial symmetry is replaced by a more or less well-defined,
bilateral symmetry. Around the mouth, but placed at some little
distance from it, is a circlet of tentacles disposed radially with
regard to the principal axis. The space between the mouth and
tentacles is known as the peristome. The tentacles may be
solid or hollow ; when hollow, their cavities are prolongations of
the coelenteron.

The walls of the sac-like body, and also the tentacles and
peristome are always composed of three layers of tissue, of which
two, the external layer or ectoderm, and the internal layer or
endoderm, are always cellular, and are coextensive and identical
with the epiblast and hypoblast of the embryo.

The third layer, lying between the ectoderm and endoderm,
varies considerably in structure and importance in different groups
of the Coelentera. Typically, it is not a cellular layer, but is of
gelatinous consistency, and is formed as a sort of secretion from
the ectoderm ; in some cases the endoderm also takes a share in
its formation. After treatment with reagents, the middle layer

6 THE ANTHOZOA

may show a fibrillar structure, which, in many cases, is undoubtedly
an artifact. It may be homogeneous and devoid of all trace of
structure, or it may contain numerous cells, which are either
branched, nucleated, so-called connective tissue cells ; nerve cells
and fibres, muscular fibres, or cells in which calcareous skeletal

Fia, I.

1.—Diagrammatic longitudinal section through a typical Anthozoan zooid. w, body wall;

ps, peristome ; b, base; ¢, tentacles; st, stomodaeum ; m, mesentery.

2.—Diagrammatic transyerse section through a typical Anthozoan zooid in the region of the
stomodaeum. ec, ectoderm; en, endoderm; mg, mesogloea; sc, sulcus; sl, suleulus.

3a.—Nematocyst of Corynactis viridis, fully everted. 8b. The same, before eversion. 3c.
The same, partly everted.

4.—Section through a typical Anthozoan mesentery with its mesenterial filament. en,
endoderm ; mg, mesogloea ; , muscle banner with supporting plications of the mesogloea.

Portion of the muscular layer of Ar r sulcata showing the nerve plexus and ganglion

cells. (1-4 original; 5 after O. and R. Hertwig.)

spicules are developed. All these cells or cell-products are in-
trusive, and are derived from one or other of the two primary
limiting layers comparatively late in life. There is no third
embryonic layer or mesoblast in the Coelentera, and for this
reason, the terms mesoblast and mesoderm being synonymous, their
middle layer is called the mesogloea, whether it be structureless

THE ANTHOZOA vi

and homogeneous, or whether it contain intrusive cells imbedded
in a homogeneous matrix.

Intimately connected with the absence of a mesoblast is the
absence of all those cavities and structures which, in the higher
metazoa, are lined by or formed from the mesoblast. There are
no coelomic spaces in the Coelentera, no haemal or blood spaces,
no specialised respiratory or nephridial systems. The musculature
is derived either from the ectoderm or from endoderm, or in cases
in which mesogloeal muscles may be spoken of, their origin from
one or other of these layers is apparent. The same may be said
of the skeletal tissues.

The Anthozoan zooid, whilst possessing the general features
enumerated above, differs from other Coelenterate zooids in some
important particulars.

The mouth in such an animal as Hydra opens directly into
the coelenteron, and the external ectoderm passes into the
endoderm at its lips. In the Anthozoan zooid the mouth does
not open directly into the coelenteron, but into a shorter or
longer tube, which projects into the coelenteron and opens into it
below. This tube is formed in the course of development as an
invagination of the ectoderm, and is therefore a stomodaeum. It
is seldom round, more generally compressed from side to side, so
as to be oval or slit-like in transverse section.

At either one or at both ends of the oval there is a groove, the
cells lining which are furnished with specially long cilia. When

_ only one groove is present, it is termed the sulcus (siphonoglyphe
_ of Hickson), where two grooves are present—one is termed the
suleus and the other the sulculus. The elongation of the mouth
and stomodaeum confers a bilateral symmetry on the Anthozoan
zooid, which is extended to other organs of the body. One may
speak of a sulcar and a suleular aspect of the body in cases in
which two grooves are present, and of a sulcar and asulcar aspect
in cases in which only one groove is present. These terms are
preferable to the older terms “ventral” and “dorsal,” which
cannot properly be applied to the Anthozoa, since they have
nothing corresponding to the ventrum and dorsum of higher
animals. It must be understood that, throughout this chapter,
‘the sulear surface corresponds to the ventral surface of other
authors, the asulcar or sulcular surface to the dorsal. The terms
sulcus and sulculus and the corresponding adjectives are due to
Haddon (33).
It is obvious from this description that the mouth of Hydra
_ and its allies does not correspond morphologically with what is
usually called the mouth, but rather with the inferior opening of
the stomodaeum of the Anthozoan zooid ; this being the region in
both groups at which the ectoderm passes into the endoderm.
20

a

8 THE ANTHOZOA

The Anthozoan zooid is further characterised by the following
anatomical features:—The coelenteron is not a simple cavity, as
in the Hydroid zooid, but is divided by a number of radial folds
of tissue into a corresponding number of radial chambers. These
radial folds of tissue are called mesenteries, or by German authors,

1.—Section through the stomodaeum of nsia ri oa tii. Diagrammatic. ec, ectoderm
showing elongate ciliated epithelial cells, ‘oh tinds of gland cells, and nematocysts. Beneath
the ectoderm is a layer of nerve fibrils. mg, mesog oe a, cont iining fibrils and a few stellate
cells; en, endoderm composed of columnar ciliated cells and containing two kinds of gland
cells.

2,—Ectoderm cells from the body wall of Corynactis viridis, partly isol lated.

8.—A portion of epithelium from the tentacle of Anemonia sulcata, consisting of three
supporting cells and one sense cell.

4.—A cnidoblast with enclosed nematocyst from the tentacle of Anemonia sulcata,

5.—Two ganglion cells from the ectoderm of the peristome of Anen a suleata.

6.—An epithelio-muscular cell from the extended tentacle of Ada a rondeletii. Ga. The

same from a contracted tentac le. 6b and 6c Endoderm cells with symbiotic zooxanthellae from

the tentacle of Anemonia

7, 7a.—Two gland cells from the stomodaeum of Anemonia leata. Tb. A flagellate cell
from the same species.

8.—A gland cell from the stomodaeum of Ané nia leata, (2 original; all the others

after O. and R. Hertwig.)

sarcosepta or simply septa. There is no objection to the use of
the term sarcoseptum, but the term septum must be avoided,
because it denotes a distinct set of structures in one of the groups
of the Anthozoa. In this chapter the term mesentery will always

THE ANTHOZOA 9

be employed. The position and relations of the mesenteries in an
ideal Anthozoan zooid may be understood by reference to Fig. I.
1 and 2. Each mesentery is attached by its upper margin to
the peristome, by its outer margin to the body wall, and by its
lower margin to the basal disc. Typically it is attached by the
upper part of its inner margin to the stomodaeum, but below
the stomodaeum it ends in a free edge, on which is placed a
thickening known as the mesenterial filament. A mesentery
consists of a middle layer of mesogloea, covered on both faces with
a layer of endoderm. The mesenterial filament is often ectodermic
in origin. The gonads or reproductive organs are borne on the
mesenteries, the germinal cells being derived from the endoderm.
The Anthozoa, like all the other Coelenterates, are provided with
special offensive weapons in the form of cnidae or nematocysts.
The nematocysts of the Anthozoa are in many cases rendered
complex by the presence of numerous spines on the whole length
of the eversible thread. In the nematocyst of Corynactis, shown
in Fig. I. 3, the spines are arranged in a double spiral. The
nematocysts of the Alcyonaria, on the other hand, are generally
simple, small, and devoid of spines (Fig. IV. 8).

The histology of the Anthozoa has been studied with some
care in the case of particular groups, especially in the Actiniae by
O. and R. Hertwig (40). In these forms the ectoderm consists of
three not very clearly defined layers: (a) The epithelial layer ; (0)
the nervous layer ; (c) the layer of muscular fibres.

Four elements are distinguishable in the epithelial layer. The
preponderating elements are the elongate, almost thread-like,
ciliated cells, whose characters may be studied in Fig. II. 1, 2,
and 3. 3 represents cells from the tentacle of Anemonia sulcata,
and it will be observed that each bears a tuft of fine and short
cilia at its broader peripheral end. 2 represents partly isolated
cells from the ectoderm of the body wall of Corynactis viridis.
In this case each attenuated cell bears a single flagellum at
its outer extremity. Similar cells are found on the mesenterial
filaments of Sagartia parasitica and other forms.

Amongst the ciliated epithelial cells are found sense cells, one
of which is shown in Fig. II. 3. They occur chiefly on the
peristome and the tentacles. Each sense cell bears a single stiff
hair at its peripheral extremity, and internally ends in several
very fine varicose fibrillae, which are continuous with the fibrils
of the nerve layer.

The third element of the ectoderm is the enidoblast shown in
_ Fig. I. 4. Each enidoblast forms, as an entoplastic product, a
single nematocyst. It is provided at its peripheral extremity
with a single stiff hair or enidocil, and internally it ends ina
fibre which branches to form numerous fibrillae like those of a

10 THE ANTHOZOA

sense cell. The fourth elements of the epithelial layer are the
gland cells, most abundant in the stomodaeum and on the mesen-
terial filaments. They are of two kinds, as shown in Fig, Il.
7 and 8.

The nervous layer of the ectoderm, shown in Fig. II. 1, con-
sists of a plexus of extremely fine fibrillae, giving in transverse
section a punctate appearance. In the depth of the fibrillar
layer are found, most abundantly at the bases of the tentacles,
bipolar and multipolar ganglion cells. These last lie directly on
the muscular layer, and are figured in Fig. I. 5, and in Fig. II,
5. The muscular layer lies directly on the mesogloea. It is
composed of very long and fine fibres, each of which bears about
the middle of its length a small mass of granular protoplasm, in
the midst of which lies the nucleus.

The endoderm consists chiefly of epithelio-muscular cells, such
as are represented in Fig. I]. 6. Each epithelio-muscular cell is
somewhat quadrangular in form in the extended condition of the
animal ; its free extremity is somewhat rounded and bears a single
long flagellum. Internally it rests upon a long and narrow
muscular fibre, which runs at right angles to it. The epithelio-
muscular cells of the endoderm contain yellow or green spherical
bodies which are symbiotic, unicellular algae, the so-called zooxan-
thellae or zoochlorellae. In addition nervous and glandular ele-
ments are found in the endoderm,

The mesogloea of the Actinians consists of fine fibres imbedded
in a homogeneous matrix. Between the fibres lie numerous
small branched or spindle-shaped cells, the so-called connective
tissue cells. In many Actinians muscular elements are imbedded
in the mesogloea.

The reader will be able to get a good general idea of the
histological elements of the Anthozoa by studying Figs. I. and
IJ. For further details he should refer to the work of O. and R,
Hertwig (40). But it must be remembered that in the Anthozoa
histological differentiation reaches its highest point in the
Actinians. In the other groups the elements are simpler.

The Anthozoa are divisible into two great sub-classes, sharply
marked off from one another by definite anatomical characters.
These are the Alcyonaria, sometimes called the Octactinia, and
the Zoantharia, sometimes called the Hexactinia, The last name
should be avoided.

ALCYONARIA—First Sup-CLASS OF THE ANTHOZOA.

The Alcyonarian zooid is distinguished by the following
characters :-— ;
There are always eight, and never more nor less than eight

THE ANTHOZOA II

tentacles, which are always hollow and pinnate, the cavities of
the tentacles extending into the pinnae.

There are eight mesen-
teries, allof whichare attached
to the stomodaeum, and may
therefore be called complete.
There is but one longitudinal,
ciliated groove in the stomo-
daeum, which will be called
the sulcus, though it is not
certain whether the groove
in the stomodaeum of the
Aleyonarian is homologous
with the sulcus of the Zoan-
tharian zooid. The proba-
bility is that it is homologous.

The mesenteries are pro-
vided with well-developed
retractor muscles, supported
on folds or plaits of the
mesogloea, which look like
branched processes in trans-
verse section, and form the
so-called muscle banners. The 1.—A typical Aleyonarian zooid showing the

eight pinnate tentacles, ¢; the two long asulcar
arrangement of the muscle wmesenteries, ml and the six shorter mesenteries,

banners of the Alcyonaria is carpe Py es digitatum.
characteristic. They are all
situated on the sulcar aspects of the mesenteries (Fig. IV. 1).

Each mesentery is provided with a mesenterial filament; but
two mesenteries, namely, the asulear pair, are longer than the rest,
and have a different form of filament. It has been shown by E.
B. Wilson (97) that the asulear mesenterial filaments are derived
from the ectoderm, the remainder from the endoderm. For the
structure of the asulcar and other mesenterial filaments, see Fig.
IV. 5 and 6.

The only exceptions to this structure are found in the arrested
or modified zooids which occur in many of the colonial Alcyon-
aria. In these the tentacles are stunted or suppressed, and the
mesenteries are ill-developed, but the sulcus is unusually large,
and is provided with specially long cilia. Such specialised zooids
are distinguished as siphonozooids, and their function is to drive
currents of water through the complex canal systems of the colonies
to which they belong (see Fig. XII. 4).

Many forms of Alcyonaria have siphonozooids in addition to
the ordinary zooids (sometimes called autozooids), and are there-
fore dimorphic; but the character is of no systematic value, for

Fic. III.

12 THE ANTHOZOA

we find dimorphism occurring in individual species of many
families which in other respects are widely separated from one
another. Only in one group, the Pennatulacea, is dimorphism of
constant occurrence.

Much attention has been paid to the skeleton of the Aleyon-

=
=
—
<2
=s
=

ord ~arenit ok,
- er cpnaesenel
— S

: —
+ veneecatihe ss
tees eieta >

Fic. IV.

1.—Transverse section through the stomodaeum of Funiculina quadrangularis.

se, sulcus.
2.—Transverse section of the same species below the level of the stomodaeum. sem, sulcar
mesenteries ; asem, asulcar mesenteries.

3.—Longitudinal section of a tentacle of Aleyoniwm digitatum. ec, ectoderm with ectodermic
nerve plexus ; mg, mesogloea ; en, endoderm.

4.—Transverse section through a portion of a mesentery of Aleyoniwm digitatum, showing
the large retractor muscle fibres borne on branched processes of the mesogloea, and the delicate
protractor muscles on the opposite face of the mesentery.

5.—Transverse section through one of the sulcar mesenterial filaments of Aleyoniwm digi-
tatum, showing the gland cells, gc, and the flagellate cells, fc.

6.—Transverse section through an asulcar filament of the same species, showing the open
groove lined by elongate ciliated ectoderm cells.

7, 7a, Tb, Te, ag’

vithelial cells from the endoderm of Alcyonium digitatum.
8.—Two nematocysts 0

Aleyonium digitatum. (1 and 2 original; the rest after Hickson.)

aria, but for taxonomic purposes it is of subordinate value. A
calcareous skeleton is present in all, with the exception of Proto-
caulon, Cornularia, some species of Clavularia, and Monoxenia,
and it is possible that spicules so minute as to have been over-
looked are present in these forms. The calcareous skeleton

THE ANTHOZOA 13

usually consists of spicules, which may be fusiform, club-shaped,
cross-shaped, or discoid; they are seldom smooth, but generally
covered with spines or warty projections. They are developed
within ectodermal cells, and are therefore entoplastic products.
Most commonly the spicule-forming cells pass out of the ectoderm
and are imbedded in the mesogloea, but Bourne (9) has shown
that in the genus Xenia the spicule-forming cells remain in the
ectoderm ; this is also the case in some members of the genus
Clavularia. In one Alcyonarian (Heliopora coerulea) the calcareous
skeleton is not spicular but lamellar, like that of Madreporarian
corals; it is formed by a special layer of cells called calicoblasts,
derived from the ectoderm.

An organic horny skeleton is frequently present, either in the
form of an external horny investment (Cornularia), or of an in-
ternal axis, as in Pennatula, Gorgonia, and others; or there may
be a half horny half calcareous axis, as in Isis; or there may
be an axis formed of calcareous spicules imbedded in horny sub-
stance, as in many Pseudaxonia.

The development of the Alcyonaria has been studied by Kowa-
levsky and Marion (69), E. B. Wilson (96), and von Koch (61).
The segmentation of the ovum is complete, and results in the
formation of a solid morula. Wilson has shown that in Renilla
the ovum divides at once into many, usually sixteen, blastomeres.
As neither von Koch nor Kowalevsky and Marion found earlier
stages of segmentation, this exceptional mode of division may
possibly be the rule amongst the Alcyonaria. After repeated sub-
division of the blastomeres of the sixteen cell stage, the solid
mass of cells is divided into two layers—an external ectoderm and
a central mass, the primitive endoderm. The coelenteron is formed
by the dissolution and absorption of the central cells of the endo-
dermic mass, the disintegrated cells being engulfed by and serving
as nourishment for the more peripheral cells which become the
definitive endoderm. There is no gastrula stage in Clavularia,
Gorgonia, or Renilla, though Haeckel has described a gastrula in
the case of Monoxenia. The embryo, at the time of the forma-
tion of the coelenteron, becomes pear-shaped, the ectoderm cells
become columnar and acquire cilia, and the larval stage known
as a planula is reached. The planula escapes from the cavity of
the parent zooid, in which the earlier stages of development have
proceeded, and swims freely in the water by means of its cilia.
There is, as yet, no communication between the coelenteron and
the exterior. After a free existence of shorter or longer dura-
tion, the embryo fixes itself by one end of its elongate body, and
a stomodaeum is formed at its opposite extremity by invagination
of the ectoderm. At the bottom of the invagination a perforation
places the coelenteron in communication with the exterior. The

14 THE ANTHOZOA

mesenteries are formed as eight radial folds of the endoderm,
which arise simultaneously at the oral end of the embryo at the
time of the formation of the stomodzal invagination. The tentacles
are formed as eight outgrowths surrounding the mouth, simple at
first, but soon acquiring lateral pinnules. The embryo is now a
zooid, and after a period of growth it gives off solenia, and from
these buds are produced, or in more differentiated colonies an
axis and other structures characteristic of particular groups are

Fic. V.

Developmental phases of Gorgonia Cavolinii, after G. von Koch. 1. A mature ovum. 2-4
ssive stages of segmentation. 5. Section through a mature and an immature ovum in
their follicles. en, endoderm ; mg, mesogloea, 6. Section of an embryo of the same stage as 4.
7. Section of a later stage showing the commencing disintegration of the central cells of the
endoderm, and the columnar ectoderm. 8, 9, and 10. Planulae in different stages of contrac-
tion. 11. A larva viewed from the oral surface to show the first traces of the mesenteries.
12. The same viewed from the side. 13. Longitudinal section through a planula of about the
same stage as 8, showing the coelenteron, coel, the endoderm, en, and the ectoderm, ec. 14,
A young zooid with simple tentacles. 15. Vertical section of a free larva with stomodwal
invagination. 16. Vertical section of an older fixed larva showing stomodaeum, st, opening
into the coelenteron. 17. A young zooid with pinnate tentacles.

developed in connection with it, The development of the meso-
gloea has been most carefully studied in Renilla by Wilson (96).
In an embryo of eight hours there is a delicate membrane lying
between the ectoderm and endoderm, on which the ectoderm cells
are planted, as on a basement membrane. This is the first sign
of the mesogloea, but the bulk of it is formed at a later stage by
deliquescence of the lower ends of the ectoderm cells and their
conversion into a gelatinoid substance. Spicules are formed in
rounded interstitial cells, which in the embryo occupy the deeper

ae

a a eee

THE ANTHOZOA 15

parts of the ectoderm, but in most Alcyonaria subsequently become
situated in the mesogloea. Fig. V. represents the principal de-
velopmental phases of Gorgonia Cavolinii, as figured by von Koch.

The sub-class Aleyonaria comprises many and highly diversified
forms, yet, as has been seen, the anatomy of the zooids is re-
markably constant throughout the group. The diversity of form
is chiefly due to the manner in which the zooids are aggre-
gated together to form colonies, and the mode of aggregation is
due, in the first place, to the mode of asexual reproduction by
budding. The form and nature of the skeleton and the mode of
aggregation of the zooids are largely interdependent, and must be
taken together as a basis of classification, the larger groups being
defined chiefly by the mode of aggregation, and their subdivisions
by the character of the skeleton. The difficulties of classification
are, however, considerable. The characters on which reliance is
placed are so inconstant, and shade so imperceptibly into one
another, that it is in many cases impossible to say where one group
ends and another begins.

Nearly all the Alcyonaria are colonial, but a few solitary forms
have been described, and these may conveniently be placed in a
separate grade under the name of
Protaleyonacea (Protaleyonaria, Hick-
son), the colonial forms forming a
second grade, Synalcyonacea.

GRADE A. PROTALCYONACEA.

The Protaleyonacea are solitary
Aleyonarian zooids, having the struc-
tural features common to the in-
dividual zooids of the sub-class. They
do not form colonies by gemmation.
The grade contains a single family,
the Haimeidae, which contains three
genera.

Family Haimeidae,M. Edw. Hai-
mea funebris, M. Edw. from the coast
of Algeria. H. hyalina, Kor. and
Daniellsen, from Norway. Hartea
elegans, P. Wright (Fig. VI.), from the
Trish coast. Monoxenia Darwinii,
Haeckel, from the Red Sea. ov

Hartea elegans, an exainple of the Protal-

It may be doubted whether all eyonacea. (After P. Wright.)
or any of the Protalcyonacea cited
above are adult forms; possibly they are the young forms of
colonies. The reproductive cells are neither figured nor described

16 THE ANTHOZOA

in Haimea and Hartea. Haeckel describes and figures the ovaries
of Monoxenia, but his account leaves much to be desired.

GRADE B. SYNALCYONACEA.

The Synaleyonacea are all colonial. The colony originates
from a mother zooid, which gives off hollow diverticula from its
base or from its lateral walls. From these diverticula buds are
formed, which grow into new zooids, and these again give off
diverticula. In this manner colonies of complex character are
formed.

It is characteristic of the Synaleyonacea that buds are never
formed directly from the mother zooid, nor yet from the daughter
zooids ; they are always formed on tubular outgrowths of the
zooids, which have variously been named stolons, nutritive canals,
endodermic canals, etc. The name stolon is the least cumbrous,
but it has been applied not only to the canals but also to structures
composed of many canals united together, and its connotation is so
vague as to be misleading in the extreme. Throughout this
chapter the canals, lined by endoderm, which are given off as
diverticula from the coelentera of the zooids comprising a colony,
will be described as solenia, from the Greek owAxjov, a little pipe
or conduit. The name stolon will be applied to the root-like
outgrowths by which many Synalcyonacea are fixed to stones,
corals, and other surfaces; and following Hickson, the name will
be extended to the membranous expansions which are formed by
the union of many flattened, root-like outgrowths.

It must be borne in mind that the cavities of Aleyonarian
zooids never communicate directly with one another, but always
by means of solenia; these may be long, much branched,
anastomosing passages, or they may be so much reduced that the
zooids seem at first sight to be in direct communication. Closer
inspection, however, will always demonstrate the intervention of
solenia.

The simplest form of budding, giving rise to the simplest
form of colony, is found in the genus Cornularia. In this genus
we find (on the authority of von Koch [54}) that the mother zooid
gives off from its base a simple, radiciform outgrowth or stolon,
which is composed of a single solenium. At a longer or shorter
distance from the mother zooid, a daughter zooid is formed as a
bud on the stolon. This gives off new stolons, and these branching
and anastomosing with one another may form a network, adhering
to stones, corals, Gorgonians, and other objects, from which zooids
arise at intervals.

A further differentiation is found in the genus Clavularia. The
colony resembles Cornularia in form and in habit of growth, but

THE ANTHOZOA 17

each stolon contains, not one, but several solenia, which branch
and anastomose with one another. In many Clavulariae the stolons
are flattened and band-like, and anastomose freely with one
another so as to form a close meshwork ; and this process of fusion
and anastomosis being carried still further, the stolons form a close
feltwork, which, like a membrane, adheres to the surface of
attachment. In all these forms the stolons and the solenia which
they contain are, with one exception, given off from the basal
region only of the zooid, and the zooids appear to, and do in fact,
stand upon the meshwork or feltwork of stolonic tubes.

A further differentiation is established when, as in Sarcodictyon,
the solenia are not confined to the base, but are also given off from
the lateral walls of the proximal extremity of the zooid. In such
a case, fusion of the walls of adjacent solenia gives rise to a
cushion-like thickening at the base of each zooid.

In Sympodium the zooids are frequently crowded together to
form dense tufts, and in such tufts (Pseudobushes of von Koch)
the cushion-like thickenings surrounding the bases of the zooids
become fused together so as to form a crust, in which numerous
solenia ramify. The proximal portions of the cavities of the
individual zooids extend through the thickness of the crust.

By further differentiation along the same lines, the colonial
forms characteristic of the Xeniidae and Alcyonidae are arrived at.
In the Xeniidae the zooids are crowded together to form bundles ;
the surface of attachment is relatively small, and the fused proximal
portions of the zooids assume the character
of a stout stem, from the flat summit of Lily
which the distal portions of the zooids
project.

In the Xeniidae the zooids are not
very intimately fused together in each
bundle. Each zooid and each solenium is
typically limited by three layers—endo-
derm, mesogloea, and ectoderm—passing
from within outwards. In Xenia the zooid
bundles are formed chiefly by fusion of
the ectoderm of adjacent zooids and their
solenia, the mesogloeal lamina of each
remaining distinct. In Heteroxenia the
mesogloea takes a share in the fusion. In
the Alcyonidae the fusion of the meso-
gloeal layers is complete. The colonies Fic. VII.

_ form lobose, generally bluntly branching — Clavularia celebensis, Hickson.
masses, from the whole surface of which
the distal moieties of the zooids, when fully expanded, project.
The fused mesogloea forms a thick mass, honeycombed by the

°

18 THE ANTHOZOA

solenia, containing spicules and spicule-forming cells, and into
this mass the proximal moieties of the zooid cavities extend.
This line of differentiation culminates in the Nephthyidae.

Starting again from the Cornulariidae, we get another line of
differentiation, culminating in the Pseudaxonia. As in the first
case a fusion of cushion-like thickenings at the bases of the zooids
results in the formation of a stout, crustaceous coenenchyme. But
the vertical growth of the colony, instead of being arrived at by
elongation of the individual zooids and their aggregation into
bundles, is effected by the upgrowth of the creeping coenenchy-
matous expansion, which deserts the surface of attachment and
expands in the water. In this condition one surface of the colony
represents the attached surface of an encrusting form and is sterile,
the other face bears the exsert distal moieties of the zooids. For
mechanical reasons the colony does not retain its flattened form,
but becomes rolled up like a paper spill; the sterile portion forms
the interior of a hollow cylinder, and the fertile portion is external.
By the excessive development of spicules on the internal (primi-
tively attached) surface, the colony becomes differentiated into a
softer cortical layer and a denser axial mass, both being penetrated
by numerous solenia. The axial mass, hollow at first, becomes
solidified in higher forms, and then it may either consist of closely
interlocked but distinct spicules, imbedded in a mesogloeal matrix
which is penetrated by solenia, as is the case in the Briareidae, or
the axis may consist of closely interlocking spicules, imbedded in
a mesogloeal matrix which is surrounded but not penetrated by
solenia, as in the Sclerogorgidae, or the spicules may be fused
together so as to form a dense calcareous axis which is not
penetrated by solenia, as in the Corallidae.

A third line of differentiation gives rise to the division
Axifera. In this case the vertical extension of the colony is
effected by the formation of a horny secretion between the
primitively crustaceous colony and the surface of attachment. The
horny secretion, growing rapidly in thickness by the superimposi-
tion of new layers, raises the colony up in the water, and
presently, by continual growth at the summit, the horny matter,
which at first was basal, comes to form an axis, supporting the
colony by which it is encrusted like a tree by its bark. The axis
may branch in various ways, and may become partly calcified, and
thus we get the various forms of the Dasygorgidae, Isidae,
Primnoidae, and Gorgonidae.

A fourth line of differentiation leads to the Pennatulidae.
The starting-point from the Cornularian ancestor is probably to be
found in the genera Telesto and Coelogorgia. In this case
vertical extension is attained by the extreme elongation of a
single zooid which, as it grows upwards, gives off solenia from

THE ANTHOZOA 19

all parts of its lateral walls, with the exception of a short region
immediately beneath the tentacles. These solenia ramify in a much
thickened mesogloeal layer which is further strengthened by the
development of calcareous spicules, and lateral buds, which appear
to be direct offshoots from the elongated mother zooid, are formed
from the solenia. Some of the daughter zooids may in turn become
elongated and give rise to lateral buds, and so an arborescent
colony is formed, as in Coelogorgia. In the Pennatulids the cavity
of the mother zooid early becomes divided by a longitudinal
partition into two halves, and an axis of peculiar wood-like texture
is formed in the partition. The greatly enlarged and elongated
body of the mother zooid serves as the stem of the colony. In the
lowest Pennatulacea the daughter zooids are irregularly distributed
over the stem, in the higher forms they become symmetrically dis-
posed with regard to the stem, and tend to form rows, the members
composing which are fused together to form leaflets or pinnae.

A fifth line of differentiation is found in the Helioporidae. In
these the solenia are not given off from the base, but ringwise at
about the middle of the length of the zooid, and immediately
beyond the zooid they anastomose so as to form a regular mesh-
work. From the nodes of the meshwork vertical solenial down-
growths are formed, and a dense calcareous lamellar skeleton is
formed from the ectoderm clothing the whole. Heliopora, the
single living representative of the family, is a peculiar and
aberrant member of the Alcyonaria, and will be described in detail
further on.

The Synalcyonacea, according to the lines of divergence which
have been sketched out above, may be divided into six orders
whose relations may be expressed as follows :—

1. Stolonifera, Hickson.

2, Aleyonacea, Verrill—pro parte.
3. Pseudaxonia, von Koch.

4, Axifera, von Koch.

5. Stelechotokea, Bourne.

6. Coenothecalia, Bourne.

We shall now proceed to review these several orders of the
Synaleyonacea.

OrveER 1. Stolonifera, Hickson.

Characters—Colonial Alcyonaria with a root-like or membranous stolon.
Zooids either entirely free from one another except at their bases, or con-

a

20 THE ANTHOZOA

nected by horizontal solenia or by lateral stolons or platforms contain-
ing solenia. Skeleton either horny or calcareous; when calcareous
spicular,

Famity 1, CornuLarmpar. The zooids are united only by their
bases, Genera—Cornularia, Lamarck. Without spicules. The stolons are
single solenia. The proximal parts of the zooids and stolons protected by
a horny sheath. Clavularia, Quoy and Gaim., spicular calcareous skeleton
present. Zooids free, borne on a membranous or retiform creeping stolon
which includes many anastomosing solenia. [Clavularia viridis, Quoy and

Fig, IX.
Skeleton of a young colony of Tubipora pur-
l, growing on a piece of dead coral. st,

i

ce, corallites; pp, platforms. (After

Hicks: mn.)

}

howing the 1
r Hickson.)

' (Atte

Gaimard, occurs in two varieties. The one variety has all the characters of
the genus, but the second variety, described and figured by Hickson (44 and
45), differs from all other members of the genus in that the zooids are
connected at varying heights above the basal stolons by tubular con-
necting stolons containing solenia, and consequently it bears a close
resemblance to Syringopora (comp. Fig. VIII. with Fig. X. 7). The
character in question, if of constant occurrence, would warrant the
placing of C. viridis in a new genus allied to the Syringoporidae and
Tubiporidae. As it is, the character must be regarded as accidental rather
than essential, but is of importance as indicating the affinities of the last-
named families with the Cornulariidae.] Sarcodictyon, Forbes, like Clavu-
laria, but the zooids are wholly retractile within cushion-like thickenings
of their bases. Sympodiwm, Ehrb., the crustaceous stolon is thickened

7
.
{
|
:
}

THE ANTHOZOA 21

locally, so that the proximal portions of the zooid cavities are sunk in a
coenenchyma, Faminy 2. Syrincoporipar. Genus—Syringopora, Gold-
fuss. This extinct genus resembles Clavularia viridis ; the cavities of the
zooids are divided by cup-shaped transverse partitions called tabulae (Fig. X.
7). Famity 3. TuprpormpaE. Genus—Tubipora, Linnaeus. The zooids

eee ; ~ i.

%
z

Fic. X.

1.—Diagram of the structure of a corallite of Tubipora purpurea, showing the tabulae in the
form of axial tubes. hp, horizontal platforms; t, solenia.

2.—A similar diagram, showing complicated tabulae.

3.—View of the inner surface of a corallite of T. purpurea, showing the numerous lacunae, h
in the walls of the corallite, and in the region of the node the larger perforations, H, through
which solenia pass into the platforms.
aa showing two tabulae broken across where one tabula (it) runs inside another

it).

5.—Diagram showing simple, flat, or cup-shaped tabulae.

6.—Portion of the edge of a growing tabula, showing how the corallum is formed by the
union of spicules.

7.—Portion of a colony of Syringopora ramulosa, showing the transverse connections between
the corallites which correspond to the solenia in the platforms of Tubipora; it, a tabula.
(After Hickson.)

are elongate, ranged side by side, and spring from a calcareous encrusting
stolon. The proximal part of each zooid is stiffened to form a firm
calcareous calyx, the corallite, into which the distal part can be retracted.
The cavity of each corallite is divided by transverse, calcareous partitions
of various form—tabulae. The individual zooids are united with one

22 THE ANTHOZOA

another by horizontal, calcareous lamellae or platforms, springing from
the levels of the tabulae and penetrated by branching solenia. New
zooids are formed by budding from the solenia of the platforms.
Famity 4. Favosiripar. The colony is basaltiform, composed of
numerous polygonal zooid tubes closely packed together. Tabulae
present and the walls of adjacent zooid tubes communicate by solenia.
Genera — Favosites, Lamarck ; Syringolites, Hinde; Stenopora, King.
Famity 5. Cotumnarmpar. This family of extinct corals, comprising

Fie. XI.

1.—Favosites gothlandica, a colony about one-half natural size from the Upper Silurian.
2.—A portion of the same colony magnified, showing the closely apposed corallites and the
perforations, solenia, placed at regular intervals on their walls, alternating with one another.
«3.—Portion of a longitudinal section of Favosites gothlandica, showing the tabulae, solenia,
and the minute lacunae in the walls of the corallites. Magnified.
All the figures original.

the genus Columnaria (Goldfuss), may provisionally be placed among the
Autothecalia, See Bourne (9).
The fossil forms of the Autothecalia were at one time placed along

with the Helioporidae and some Madreporarian corals in a group Tabulata. |

Hickson (42) has clearly demonstrated the relations of Tubipora to
Syringopora, Syringolites, and Bourne has shown that Favosites must be
ranked with these forms rather than with the Helioporidae. There is a
great resemblance between the extinct Syringopora and the living
Clavularia viridis, and Hickson may be held to have established that
Syringopora, Tubipora, and their allies have been derived from a Cornu-

:

———

THE ANTHOZOA 23

larian ancestor resembling (. viridis. The structure of Tubipora and
Favosites is shown in Figs. IX., X., and XI.

OrDER 2. Alcyonacea, Verrill (pro parte).

Characters—The colony consists of bunches of elongate, cylindrical
zooids which, in their proximal portions, are connected together by
numerous anastomosing solenia, and are compacted into a. fleshy mass,
the coenenchyma, by fusion of their own walls and those of the solenia.

Fic. XII.

1.—A sinall colony of Aleyoniwm palmatum, Pallas, with expanded zooids. (Original.)

2.—Vertical section through a small colony of Aleyonium digitatum, Linn., showing the
elongated zooid cavities. (Original.)

3.—A colony of Sarcophytwm pulmo, Esper, showing the pileus, P, bearing zooids, and the
barren stem, st. One-half natural size. (Original.)

4.—Diagrammatic vertical section through a portion of a colony of Sarcophytum pulmo,
showing the retracted autozooids, az, and the siphonozooids, sz, connected by a network of
solenia. (After Moseley).

The coenenchyma thus forms a stem, sometimes branched, from the
surface of which the free portions of the zooids project.

Famity 1. Xenipak, Gray (pro parte). The zooids are not retractile.
Spicules in the form of minute, feebly calcareous discs, often confined to
the ectoderm. The colony consists of a stout, fleshy, sterile stem, some-
times bearing short lobose branches, on the expanded upper surface of
which the free moieties of the zooids are borne, Genera—AXenia, Savigny.
Colony monomorphic. Heteroxenia, Kélliker. Colony dimorphic, bearing
autozooids and siphonozooids. Faminy 2, Aucyonipax, Verrill. The
colony a fleshy stock, sometimes simple and lobose, sometimes irregularly

21

24 THE ANTHOZOA

branching, the extreme basal portion of the stock generally devoid of
zooids and forming a stem. Zooids elongate, imbedded in coenenchyma
up to the stomodeal region, which is completely retractile within the
lower portion. Spicules mesogloeal, of various form, commonly fusiform,
and furnished with spines and warty projections. Genera—(a). Mono-
morphic forms. Aleyoniwm, Linnaeus ; Paralcyonium, M. Edw. ; Sarakka,
Danielssen. ((). Dimorphie forms. Sarcophyton, Lesson ; Lobophytum,
Marenzeller ; Anthomastus, Verrill ; Nannodendron, Danielssen, FAMILY
3. NEPHTHYIDAE. The zooids form upright colonies, consisting of a more

Fic. XIII.

1.—Clavularia coerulea, Ehrb, A Clavularian colony with a membranous stolon.

2.—Ammothea arborea, Forsk. A member of the sub-family Spongodinae.

3.—A group of zooids of the same, magnified.

4.—Lemnalia nitida, Verrill. A member of the sub-family Siphonogorginae.

5.—A terminal branchlet of the same, magnified.

6.—Heteroxenia elizabethae, KOM. A colony divided vertically to show the elongate cavities
of the autozooids, az, between the exsert portions of which are siphonozooids, sz.

or less sterile trunk, and variously ramified branches bearing terminal
zooids or clusters of zooids. The tentacular region of the zooid is not
retractile into the gastral region, but the tentacles, when at rest, are
simply folded over the oral disc. The wide canals which run longi-
tudinally in the stem and larger branches are continuations of the
cavities of the principal zooids of the clusters. There are two sub-
families. 1. Sponcoprnar. The partitions between the stem canals
contain few or no spicules. Genera—Nephthya, Savigny. The zooid
heads beset with long and large, but not projecting spicules, Spongodes,
Lesson. The zooid heads protected by projecting tufts of long spicules.

—————— —— ee ee

THE ANTHOZOA 25

Ammothea, Savigny. The zooid heads soft, containing few and small
or no spicules. Huwnepthya, Verrill; Voeringia, Danielssen ; Fulla,
Danielssen ; Parathrobius, Danielssen; Gersemia, Danielssen; (Ger-
semiopsts, Danielssen ; Drifa, Danielssen ; Duva, Kor, and Danielssen.
2. SrpHonocorarvar. ‘Abundant spicules present in the partition
walls of the stem canals, giving stiffness and consistency to the colony.
Genera— Siphonogorgia, Kélliker ; Paranephthya, Wright and Studer.
Scleronephthya, Wright and Studer; Chironephthya, Wright and Studer ;
Lemnalia, Gray.

OrpvrER 3. Pseudaxonia, G. von Koch.

Characters—Synalcyonacea forming upright branched colonies. The
zooid cavities short, the zooids imbedded in a coenenchyma containing
ramifying solenia and numerous spicules. The coenenchyma differentiated
into a cortical and a medullary portion, the latter containing spicules
different from those of the cortex, densely crowded together and sometimes
cemented together to form a supporting axis.

Famity 1. BriaREIDAE. The medullary substance consists of closely
packed but separate spicules. There are twosub-families. 1. BRIAREINAE.
The medullary mass is penetrated by solenia. Genera—Solenocaulon,
Gray ; Leucoella, Gray ; Semperina, Kolliker ; Suberia, Studer ; Anthothela,
Verrill ; Paragorgia, M. Edwards; Briarewm, Blainville. 2. Sponeio-
DERMINAE. The medullary mass is devoid of solenia. Genera—Spongio-
derma, Kolliker; Titanidewm, Agassiz ; Ilicigorgia, Ridley. Fammy 2.
ScteroGoRGIDAE. The medullary mass forms a distinct axis consisting of
closely packed elongate spicules with dense horny sheaths. The axis
does not contain solenia, but is surrounded by longitudinal canals, 7.e.
by large solenia which are connected with the zooid cavities by smaller
ramifying solenia. Genera—Subherogorgia, Gray ; Keroeides, Wright and
Studer. Faminy 3. Meriroprpar. The medullary mass forms a distinct
axis, which exhibits alternate calcareous and horny segments. The former
(internodes) consist of fused calcareous spicules surrounded by a trace of
horny substance ; the latter (nodes) consist of horny substance containing
few, separate, calcareous spicules. Genera—(a). The axis penetrated by
solenia, Melitodes, Verrill ; Mopsella, Gray. (8). The axis not penetrated
by solenia. Wrightella, Gray ; Parisis, Verrill. Famity 4. CoRALuIpAr.
The axis is a dense, calcareous mass formed by fusion of spicules. Genera
—Corallium, Lamarck ; Plewrocorallium, Gray.

Corallium rubrum, the precious red coral of commerce, is found in the
Mediterranean sea, chiefly on the coasts of Africa, but also in the neigh-
bourhood of Sardinia and Corsica, and at some places on the littoral of
Italy and Provence. It has, from time immemorial, been the object of an
extensive fishery, on account of the value of its hard, red, calcareous axis,
for the manufacture of jewellery and ornaments. The colonies are found
attached to rocks at depths varying from 15 to 120 fathoms. The fisher-
men use a special form of tangle to procure it. From its beauty and
importance as an article of commerce, the red coral has attracted the
attention of zoologists from an early period. De Lacaze Duthiers (70)
has written an exhaustive and beautifully illustrated memoir on this

26 THE ANTHOZOA

species which the reader should consult for details of the anatomy and
development.

Although von Koch, some years since, demonstrated the essential
difference between the Pseudaxonia and the Gorgonians or true Axifera,
many subsequent authors, although they have accepted von Koch’s con-
clusions, have persisted in bringing the two groups together in the order
Gorgonacea. It is evident, from what has been said above, that the
Pseudaxonia and the Axifera form two distinct lines of descent, diverging
from a common Cornularia-like ancestor, and therefore they must be
classed as two distinct branches of the order Synaleyonacea. The sole
reason for uniting the two branches in one order is that the higher forms
of the two show a remarkable superficial resemblance to one another, a
resemblance which is the more remarkable from the parallelism of forms
like Melitodes and Isis, both of which, though belonging to widely
separate families, have an axial skeleton composed of alternate horny and
calcareous segments. The resemblance, striking though it may be on
superficial examination, disappears on closer comparison.

But whilst there is ample justification for keeping the two groups
apart, it is not suggested that the line of descent attributed to the Pseud-
axonia is beyond criticism. Whilst it is quite possible, and may seem
probable, that Leucoella and Solenocaulon are on the direct line, of
descent of the higher forms of the Pseudaxonia, there is nothing that
can be urged against the view put forward by Klunzinger (49) that
the Briareidae are descended from forms like the Siphonogorginae, the
medullary mass being formed by excessive development of spicules in the
partitions separating the stem-canals. The majority of the Pseudaxonia
are monomorphic, but dimorphism occurs sporadically in the genera
Paragorgia and Corallium.

Orver 4. Axifera, von Koch.

Characters—Synalcyonacea, forming colonies consisting of a coenen-
chymatous rind investing a horny or calcified axis. The axis may be
horny, or composed of a calcified, horny substance, or may consist of
alternate segments of calcified and horny substance ; it never contains
solenia, and is never formed of fused spicules. The coenenchyme com-
pletely invests the axis, and contains solenia and calcareous spicules
imbedded in the mesogloea.

The Axifera (or Gorgonacea) have been the subject of an admirable
memoir by G. von Koch (61), to which the reader should refer for
morphological and embryological details. The characteristic feature of
the group is the axis, which is horny, or consists of a horny basis im-
pregnated with salts-of-lime. It is surrounded by a definite epithelium,
which is ectodermic, and is derived from the basal ectoderm of the
mother zooid of the colony. The mother zooid secretes at its base a
horny plate, which lies between the basal ectoderm and the surface of
attachment. This is the primordium of the axis. It rapidly increases
in thickness, and forms a short column, rounded at the upper end. This
column projects upwards into the coelenteron of the mother zooid,
carrying before it the three layers, ectoderm, mesogloea, and endoderm.

—s. oo oe

THE ANTHOZOA 27

It always lies eccentrically in the coelenteron, and becomes fused partly
with the body wall, partly with the neighbouring mesenteries. Before
the axis has reached the level of the stomodaeum, the surrounding parts
of the primitive coelenteron become differentiated, and take on the char-
acters of solenia, which, as growth proceeds, become more differentiated
and distinct. At a later stage the distal moiety of the zooid is separated
by a constriction from the moiety which surrounds the axis, and thus
comes to look like an appendage of the stem. The first daughter zooid
is formed as an outgrowth of a solenium on the side of the axis opposite

Fic XIV.

1.—A colony of Gorgonia Cavolini, von Koch. One-quarter natural size.

2.—Extremity of a branch of Gorgonia Cavolini, showing zooids in various stages of con-
traction. Magnified.

3.—Optical section through the mother zooid of a colony of Gorgonia Cavolini, showing the
formation of the axis, 4, as a secretion of the basal ectoderm.

4.—Optical section through an older stage with two zooids. A, axis.

All the figures after G. von Koch.

to the zooid already formed, and successive zooids are formed in the same
manner, alternately on either side of the axis. In the fully grown
colony the cortex or coenenchyme consists of a thickened mesogloea, in
which lie solenia, whose course is mainly longitudinal, i.e. parallel to
the axis. In the smaller branches of some forms eight solenia are present,
which probably represent the eight inter-mesenterial chambers of the
primary zooid. In the main stem the number is usually greater. The
solenia, both in stem and branches, anastomose freely with one another,

28 THE ANTHOZOA

From this description it is clear that the relation of the zooid cavities to
the axis is much more intimate in the Axifera than in the Pseudaxonia.

Famity 1. DasyGoreimpar. Colonies simple or branched. Axis
horny and calcified. Zooids large, placed far apart, non-retractile, infold-
ing their tentacles over the oral disc when at rest. Spicules smooth,
needle-like or fusiform. Genera — Dasygorgia, Verrill ; Chrysogorgia,
Duchassaing and Michelotti. Famiry 2. Istpar, The axis consists of
alternate horny and calcareous segments, the calcareous matter being
amorphous. There are three sub-families. 1. CERATOISIDINAE. Spicules
in the form of smooth needles. Genera—Bathygorgia, P. Wright ;
Ceratoisis, P. Wright ; Callisis, Verrill; Acanella, Gray; Isidella, Gray ;
Sclerisis, Studer. 2. Mopsrernar. Spicules in the form of dentate scales.
Genera— Mopsea, Lamouroux; Primnoisis, Wright and Studer; Acan-
thoisis, Wright and Studer. 3. Ismprnak. Zooids retractile in a thick
coenenchyme ;_ spicules stellate, warty. Genus — Isis, Linnaeus.
Famity 3. Prinorar. Axis horny, calcified. Zooids with a caly-
cine moiety stiffened by calcareous scales. Tentacular moiety retractile
within the calyx, the opening of which can be closed by an operculum
of eight scales. SuBp-Famity—CALLOzOSTRINAE. Genus— Callozostron,
P. Wright. Sus-FAmMmyY—CaALYPTROPHORINAE. Genus— Calyptrophora,
Gray. Susp-Famity— Prioinornar. Genera— Primnoa, Lamouroux ;
Stachyodes, Wright and Studer ; Calypterinus, Wright and Studer ; Stenella,
Gray ; Thouarella, Gray; Amphilaphis, Wright and Studer ; Plumarella,
Gray ; Primnoella, Gray. Famity 4. Muricerpar. Axis horny; zooids
divided into three regions—a proximal calycine, a median retractile, and
a tentacular non-retractile. Tentacles at rest infolded, provided at their
bases with an armour of stout spicules, forming a false operculum. There
are twenty-three genera of Muriceidae, the best known being Acanthogorgia,
Gray ; Paramuricea, Kolliker ; Villogorgia, Duch. and Mich.; Bebryce, de
Phillipi; Acis, Duch. and Mich.; Humuricea, Verrill. Faminy 5. PLEx-
AURIDAE. Axis horny or horny and calcified ; zooids partially or wholly
retractile, without opercula, Genera—Lunicea, Lamouroux ; Plexawra,
Lam. ; Plexaurella, Kolliker ; Psammogorgia, Verrill ; Eunicella, Verrill;
Platygorgia, Studer. Famrity 6. Gorcontpar. Colonies erect, branched,
usually in one plane. Zooids bilaterally or biradially disposed on stem
and branches ; retractile. Spicules small, fusiform. Genera—Gorgonia,
Linnaeus ; Eugorgia, Verrill; Platycaulos, Wright and Studer, Lophogorgia ;
M. Edwards ; Stenogorgia, Verrill ; Callistephanus, Wright and Studer;
Swiftia, Duch, and Mich.; Danielssenia, Grieg ; Xiphigorgia, M. Edw.;
Hymenogorgia, Valenciennes ; Phycogorgia, Val.

Orprr 5. Stelechotokea.

Under this name are (here for the first time) included all those Synal-
cyonacea in which a much elongated mother zooid forms the stem or axis
of the colony, the daughter zooids being borne as lateral buds upon the stem.
The colonies are erect, simple, or branched, or may be plumose. When
they are branched, secondary zooids, developed as buds from the stem or
mother zooid, form the axes of the branches, and tertiary zooids are
budded off on each side of them, The secondary and tertiary zooids, though

THE ANTHOZOA 29

they appear to be borne directly by the mother zooid, do not communicate
directly with the cavity of the latter, but secondarily by means of solenia,
which ramify in the greatly thickened mesogloea of the walls of the
mother zooid. The branch thus defined includes forms which have
hitherto been classified with the Cornulariidae, and are, in truth, not
easily separable from that family. But they exhibit, in their mode of
budding and in the disposition of the secondary zooids around a central
zooid, characters which mark them off distinctly from their nearest

_
ata

.

Sere
siptee

=o Sere
~t+-

~<

dak

“ety

“a

Fic. XV.

1.—Portion of a colony of Carijoa arborea, Wright and Studer. About one-third natural size.
2.—Portion of stem of Telesto arborea. Magnified, showing the zooids.

3.—Extremity of branch of Coelogorgia. Magnified, showing the zooids.

4.—Coelogorgia palmosa, M. Edw. Portion of a colony about one-third natural size.
5.—Spicules of Coelogorgia.

(1 and 2 after Wright and Studer ; 3 to 5 original.)

Cornularian allies, and they appear to lead on to the well-defined group
of the Pennatulacea.

Section 1. Asiphonacea. Characters—Colony erect, simple, or branch-
ing, consisting of an elongated, axial zooid with thickened walls containing
solenia, from which secondary zooids are formed, Skeleton in the form
of dentate dises or warty spindles ; a horny or calcified axis absent. The
cavity of the axial zooid is not divided by a partition.

Famity 1. Tevestmar. From a membranous or ramifying stolon
individual Clavularia-like zooids, the body walls of which contain solenia,
arise. Certain of these grow out to form long zooid tubes, or axial zooids,

30 THE ANTHOZOA

and from their walls lateral zooids are given off. Genera—Telesto,
Lamouroux. The colony is low and only slightly ramified. Spicules
in the form of broad dentate discs or ramified and irregular. Carijoa,
F. Miiller. The colonies form tall ramified masses. The axial zooids
large, lateral zooids minute. Spicules rod-like with few spines cemented
together by a horny substance. ([Telesto is usually placed among the
Cornulariidae, which it resembles in many respects, in the ramifying or
membranaceous stolon, and in the manner in which isolated zooids arise
from the stolon. But it differs from them in the manner of budding
from axial zooids. The same character removes it from the Stolonifera,
as defined above, though the presence of a stolon suggests its inclusion in
that group. It must in any case be regarded as a link between the
Stolonifera, especially the Cornulariidae, and the next family.] Famriy
2. CoELocorGiDAE. The colony arborescent, attached by stolon-like
processes. The stem formed by an axial zooid, with thickened coenen-
chymatous walls. Branches formed by axial zooids of the second order,
and branchlets by axial zooids of the third order, borne either on two
sides or in spirals by the main stem. Spicules straight or curved,
bearing lateral processes. Genus—Oboelogorgia, M. Edwards.

Section 2. Pennatulacea. Characters—The colony consists of more
or less numerous lateral zooids borne by a much elongated axial zooid.
The colony is free (except in Gondul), and the axial zooid forms a scapus
or stem, which is again subdivided into a proximal calamus or peduncle,
sunk into the sand or mud and destitute of zooids, and a distal rachis
which bears two kinds of zooids—autozooids and siphonozooids. Thus
the colonies are always dimorphic. Early in development the cavity of
the axial zooid is divided into two by a longitudinal partition. The
majority of the Pennatulacea have an axis which is composed of a
calcified horny substance and is generally described as having a willowy
texture. When it is present it runs along the middle of the septum
dividing the cavity of the axial zooid, and two additional stem canals are
formed as cavities in the septal tissue on either side of the axis, making
four stem canals in all) The mesogloea of the stem is much thickened
and is penetrated by numerous solenia which communicate on the one
hand with the stem canals, on the other hand with the coelentera of
the autozooids and siphonozooids borne on the rachis. The endodermic
musculature is largely developed, especially in the stem where it forms,
in the higher members of the group, an external longitudinal and an
inner circular layer.

The higher members of the Pennatulacea have a distinct bilateral
symmetry, due to the zooids being borne like the barbs of a feather on
two sides of the rachis only, leaving a sterile‘band on the two remaining
sides. Hence four surfaces may be distinguished, named hy Kolliker
the dorsal and ventral sterile surfaces, and the two lateral zooid-bearing
surfaces. The names dorsal and ventral are in themselves objectionable,
and Kolliker’s application of them was unfortunate, for Jungersen (48)
has shown that the so-called ventral side of the Pennatulid colony is, in
fact, the asulear, or as it is frequently called, the dorsal aspect of the
terminal zooid. It is evident that the arbitrary use of the terms dorsal

———

:

a ae

THE ANTHOZOA 31

and ventral leads to confusion, and to avoid ambiguity the following
terms will be applied to the several regions into which the rachis of the
bilaterally symmetrical Pennatulacea may be divided :—The face of the
rachis which is sterile and coincides with the asulcar aspect of the
terminal zooid, 2.e. with the ventral surface of Kdélliker, will be called
the prorachis. The opposite face, equivalent to Kélliker’s dorsal surface,
is the metarachis. The two remaining faces, the lateral surfaces of

Fic. XVI.

1.—Virgularia Bromleyi, K6ll., from the prorachidial aspect.

2.—Kophobelemnon Burgeri, Herklots ; metarachidial aspect.

3.—Stachyptilum Macleari, KOll. ; metarachidial aspect.

4.—Umbellula Carpenteri, KOll.; metarachidial aspect.

5.—Pennatulu phosphorea, Linn. ; metarachidial aspect.

6.—Section of the rachis of Pennatula phosphorea bearing a single pinna. a, axis; b, meta-
rachidial ; c, prorachidial ; dd, pararachidial stem canals ; sp, siphonozooids ; z, autozooids.

7.—Renilla reniformis, Pallas. (1 to 4 after Kolliker, 5 to 7 original.) In all the figures.
R, rachis ; P, peduncle ; sp, siphonozooids ; 2, zooids.
Kolliker, are the pararachides. Milnes Marshall (77) has shown that the
symmetry of the lateral, or as we may now call them, pararachidial zooids,
bears a definite relation to the symmetry of the colony. The asulcar
aspect of each zooid is turned towards the stem, and therefore may be
ealled axial, the sulcar aspect is turned away from the stem and is
therefore abaxial. When, as is the case in Pennatula and Pteroeides,
several elongated zooids are fused together side by side to form leaflets or
pinnae, these are always situate on the pararachides and are inserted
diagonally on those surfaces. Hence in each leaflet two surfaces may be

distinguished—an axial, turned towards the rachis, and an abaxial,

32 THE ANTHOZOA

turned away from it. There are also three edges in each pinna—a basal,
attached to the rachis ; a lower, destitute of zooids ; and an upper, more
or less convex, bearing zooids. The axis of the Pennatulacea, when
present, is entirely enclosed within the tissues and is surrounded by an
epithelium. There is not sufficient evidence to show from what layer
this epithelium is derived, but the evidence, as far as it goes, points to
its being of endodermic origin. The development of Renilla has been

Fic. XVII.

1.—A young colony of Pennatula phosphorea
seen from the right side. P, the calyx of the
mother zooid ; Z, the first siphonozooid ; pl, the
first lateral autozooid formed as a bud from P ;
p*, the third lateral autozooid.

2.—A somewhat older colony seen from the
asulear aspect. zl, 22, lateral siphonozooids
formed at the bases of pl, p2, the first and
second lateral autozooids ; , Successively
formed lateral autozooids.

3.—Diagrammatic section through the ter-
minal autozooid and siphonozooid of a young
colony of Pennatula phosphorea. S, sulcar inter-
mesenterial chamber; As, asulear chamber ; st,
stomodaeum of siphonozooid.

4.—A section of the same colony through
the autozooid, in 2. S, sulcar chamber of the
axial zooid ; As, asulear chamber ; the two are
separated by the transverse partition, in which
two lateral canals (stem canals)are being formed ;
p', py, lateral autozooids.

5.—A section somewhat lower down. The
axis X is being formed in the partition between
the two lateral chambers; Z, a siphonozooid-
(All the figures after Jungersen.)

thoroughly studied by E. B. Wilson (96), whose memoir should be
consulted by the reader; but Renilla has no axis, and Jungersen was
unable to obtain stages of Pennatula phosphorea young enough to throw
light upon the question. The growth of the peduncular septum in
Renilla has been fully described by Wilson, and the same mode of
development apparently holds good for Pennatula. It arises as a double
fold of endoderm containing a delicate lamina of mesogloea at the basal
end of a larva of forty hours. This fold grows rapidly upwards and
becomes continuous with the asulcar mesenteries at the point where
these unite, as they do in Renilla, with the asulco-lateral pair. Thus
the coelenteron of the mother zooid is early divided into two cavities by
a transverse partition which separates the asulcar portion of the coelenteron
from the sulcar portion containing the mesenteries The lower or
proximal portion of the mother zooid becomes, in course of growth,

THE ANTHOZOA 33

»

: enormously larger than the distal portion, and forms the peduncle and
rachis of the colony, its cavity being divided by the septum into a
prorachidial (asulcar or ventral of Kolliker) and a metarachidial (sulcar or
dorsal of K®élliker) chamber. The distal portion of the mother zooid
becomes at an early period nothing more than a relatively minute

_ appendage upon the upper part of the stem which has been developed
from it. At the base of the distal or calycine portion of the mother
zooid, a bud, formed on the asulcar side, forms the first or terminal
siphonozooid. The lateral zooids are formed as buds on either side of
the terminal zooid, and as each is developed a siphonozooid is formed at
its base. The pinnae are formed by the development of secondary buds
at the bases of the primary pararachidial autozooids. In the course of
growth the proximal portions of the rows of autozooids so formed become

_ fused together, the distal ends remaining free and forming small calices,
strengthened by a crown of eight points formed by spicules, and the
tentacular portions of the zooids are retractile within the calices.

The development of the Pennatulid colony and the formation of the
pedunecular septum will best be understood by a study of Fig. XVII.
The existing families of the Pennatulaceae appear to have diverged from
an ancestral form resembling Protocaulon molle. The lines of divergence
may be briefly indicated as follows :—From an original form in which
simple sessile autozooids, each with a siphonozooid at its base, were
borne on either side of an axial zooid, differentiated into peduncle and
rachis. (1) The autozooids have become more numerous, have encroached
on the whole surface of the rachis, and the siphonozooids, multiplying in
number, have filled up the spaces between the autozooids. Such a
condition is found in the Veretillidae, in which a bilateral symmetry is
replaced by a radial symmetry. (2) The autozooids, whilst increasing in
number, are confined to two opposite aspects of the rachis, and there
form, at first indistinct, afterwards distinct rows. The siphonozooids
also increase in number, and lying between the bases of the autozooids,

occupy the remainder of the pararachidial surfaces. From this condition,

realised in the Funiculinidae, differentiation proceeds in two directions.

(a) The autozooids are confined to the upper part of the rachis, and

are finally grouped in an umbel at its summit, the remainder of the

rachis bearing siphonozooids only on the pararachides, e.g. the Umbell-
ulidae. (8) The autozooids are disposed in oblique rows on the
pararachides, and their proximal portions are fused so as to form leaf-like
appendages of the rachis or pinnules. In the family Virgularidae the
autozooids are short and the pinnules are small and inconspicuous, in the
Pennatulidae the autozooids are much elongated and form conspicuous
pinnules. The family Géndulidae is derived from the Pennatulidae by
suppression of the peduncle, the colony, consisting of rachis and pinnules,
being fixed by the proximal end of the rachis. The family Renillidae
appears to have branched off from the Umbellulid stem ; the peduncle is
short, the rachis is much expanded and forms a kidney-shaped expansion,
bearing on its upper surface numerous irregularly distributed autozooids,
amongst which are situated groups of siphonozooids. The following
classification of the Pennatulacea is founded on Kéolliker’s work, but is

—

|

34 THE ANTHOZOA

modified to exhibit the relations sketched out above, and to harmonise
with the grouping of the other branches of the Aleyonaria :—

Sus-Srecrion A. Rachis without pinnules, autozooids sessile, disposed
on both sides of the rachis in single series or in indistinct rows.

Famity 1. Prorocau.ipak. Autozooids sessile, without calices, disposed
alternately on each side of the rachis in a single row. Spicules absent.
Genus—Protocaulon, Kolliker. Faminty 2. Proroprinipar. Autozooids
sessile, with calices, disposed alternately on each side of the rachis in
a single row. A single siphonozooid at the base of each autozooid.
Spicules present. Genera—Protoptilum, Kolliker ; Lygomorpha, Koren
and Danielssen ; Microptilum, Koll. ; Leptoptilum, Koll. ; Trichoptilum,
Koll. ; Scleroptilum, Koll. Famtty 3. KopHoBeLeMNoNIDAE. Rachis
longer than peduncle, cylindrical, bearing on the pararachides retractile
autozooids in indistinct rows. Siphonozooids numerous. Spicules present.
Genera—Kophobelemnon, Absjérnsen ; Sclerobelemnon, Koll. ; Bathyptilum,
Koll. Famity 4. UmpBeniutmar. Rachis short, bearing autozooids at
its distal end only, where they are frequently grouped into an umbel.
Siphonozooids scattered over the pararachides. Genus—Umbellula, Lam.

Sus-Section B. Rachis without pinnules. Autozooids sessile, borne
on the pararachides in distinct rows.

Famity 5. ANTHOPTILIDAR. The autozooids without calices. Genus
—Anthoptilum, K6ll. Faminy 6. Funtcurinipar. The autozooids have
calices. SuB-Famtty—FvUNICULININAE, with prorachidial siphonozooids.
Genera—Funiculina, Lam. ; Halipteris, Koll. Sup-Fammy—Stacuy-
PTILIHAE, Without prorachidial siphonozooids, Genus—Stachyptilum, Koll.

Sus-Secrion C. Rachis with pinnules formed by fused rows of
autozooids borne on the pararachides.

Famity 7. VIRGULARIDAE. Pinnules small. Sus-Famtty—Vir-
GULARINAE. Pinnules without a calcareous plate. Genera—Virgularia,
Lam. ; Scytalium, Herklots; Pavonaria, Koll. Sus-Famttby—Sry.atv-
LINAE. Pinnules with a calcareous plate. Genera—sStylatula, Verrill ;
Dubenia, Kor.and Dans. ; Acanthoptilum, Koll. Famtny 8. PENNATULIDAE.
Pinnules large. SuB-FaAMILY—PENNATULINAR, Siphonozooids on prorachis,
metarachis, and pararachides, but not on pinnules. Genera— Pennatula,
Lam.; Leioptilum, Verrill; Ptilosarcus, Gray ; Halisceptrum, Herklots.
Sus-FamiLy—Preroripipak. Siphonozooids on the pinnules. Genera—
Pteroeides, Herklots ; Godefroyia, Koll. ; Sarcophyllum, Koll. Famity 9.
GénDULIDAE. Peduncle absent; colony attached by proximal end of
rachis. Genus—(Géndul, Kor. and Dan.

Sus-Secrion D. Autozooids sessile, disposed over the whole surface
of the rachis, which therefore has no pro-, meta-, and pararachides, and
the symmetry of the colony is radial.

Famity 10. VeRETILLIDAR. SuB-FAMILy—CAVERNULARINAE. Spicules
elongate. | Genera—Cavernularia, Valenciennes ; Stylobelemnon, Koll.
Sus-Faminy—Lirvarmar. Spicules short. Genera—Lituaria, Val. ;
Veretillum, Cuvier ; Policella, Gray ; Clavella, Gray.

Sus-Srcrion E. The rachis forms a broad reniform expansion bearing
autozooids and siphonozooids on its surface. Axis absent.

Famity 11. RenIvumpar. Genus—Renilla, Lam.

:
.

THE ANTHOZOA 35

OrprErR 6. Coenothecalia.

Characters—Synaleyonacea with a calcareous skeleton composed of
lamellae of calcite forming a dense corallum resembling that of the

<0 2
1p. “Py woe
S, Si iSee
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Fic. XVIII.

1.—Surface view of a portion of a fully grown colony of Heliopora coerulea, Pall., showing
two calices with their pseudosepta ; the openings of the coenenchymal tubules, the superficial
echinulations, and the shallow canals between them in which the superficial network of solenia
lies in the living condition.

2.—A single zooid with the adjacent soft tissues of Heliopora coerulea, as seen after removal
of the skeleton by decalcification; semidiagrammatic. Z1, the distal retractile moiety of the
zooid, bearing eight pinnate tentacles ; Z2, the proximal calicular moiety of the same; ec, the
continuous sheet of ectoderm which clothes the surface of the colony; sp, the superficial
network of solenia lying directly beneath the ectoderm ; ct, coenenchymal tubules.

3.—Diagram illustrating the mode of growth and architecture of a colony of Heliopora. 71,
calyx of mother zooid ; 7”, 7%, etc., calices of daughter zooids successively formed amongst the
coenenchymal tubules ; ¢t, tabulae.

4.—Surface view of a tangential section through the surface of a colony of Heliolites porosus,
Goldfuss, showing three calices, each with twelve pseudosepta imbedded in a coenenchyme con-
sisting of numerous vertical coenenchymal tubules (solenia) of approximately hexagonal shape.

56.—Diagram illustrating the essential structure of the corallum in Heliopora and Heliolites.
Ct, coenenchymal tubules, the walls of each of which are composed of twelve separate laminae,
which take a share in the composition of the walls of six adjacent tubules. In the centre of the
figure a calicular cavity is indicated formed by the arrest, complete or partial, of a group of
nineteen coenenchymal tubules numbered 1-x1x. The outlines of the arrested tubules are
indicated by dotted lines.

imperforate Madreporaria, and developed from a specialised layer of ecto-
derm cells (calicoblasts). The corallum exhibits a number of larger
calices, provided with a variable number of radial pseudosepta, sunk in a
coenenchyme composed of numerous closely set vertical tubules, with
calcareous walls, which are disposed vertically to the surface of the

36 THE ANTHOZOA

corallum., Both calices and coenenchymal tubules are closed below by
transverse calcareous partitions or tabulae. The walls of the calices and
coenenchymal tubules are not separate and independent, but the calcareous
lamellae forming the walls of one tubule enter into the composition of
the walls of adjacent tubules, and the calyx walls and the pseudosepta are
formed by the walls of adjacent coenenchymal tubules. The colony consists
of zooids and solenia. The zooids exhibit a proximal moiety imbedded in the
calyx and a distal moiety which can be invaginated within the calicine
portion. Solenia are given off radially from the level where these two
regions pass into one another, and anastomose with one another to form a
more or less regular superficial network, which covers the surface of the
corallum. From the nodes of the network blind solenial downgrowths pro-
ject vertically into the coenenchyme, each occupying a coenenchymal tubule.

The Coenothecalia are represented by a single living genus Heliopora,
but the group was more largely represented in Palaeozoic times. Helio-
lites from the Silurian and Devonian is closely allied to Heliopora. The
presence of septiform radial lamellae in the calycles was long regarded as
a reason for placing Heliopora and Heliolites among the Zoantharia, but
Moseley (80) demonstrated the typical Alcyonarian structure of the
zooids of Heliopora, and subsequent investigations have shown that this
genus, with others which have a similar structure of corallum, must be
placed in a separate branch of the Alcyonaria. For details of the
anatomy of Heliopora the reader is referred to Moseley’s memoir, and to
Bourne (9).

Fig. XVIII. 2 shows the relations of the soft parts of the Helioporid
colony, and 5 shows how the walls of each coenenchymal tubule are
formed of twelve pieces common to that and the six adjacent tubules, the
calyx being formed by the arrest in growth of a group of seven central
tubules and the partial arrest of twelve peripheral tubules, the walls
of which give rise to the pseudosepta. The most remarkable features in
Heliopora, in addition to the laminar calcareous corallum, are the limita-
tion of the solenial outgrowths to the middle region of the zooid, and the
formation of vertical tubular down-growths from the solenial meshwork,
forming the so-called coenenchymal tubules. These were originally con-
sidered to be extremely degenerate siphonozooids, but they have no traces
of zooidal structure, and must rather be considered to be a specialised part
of the solenial system, associated with the peculiar form of the corallum.

Famity 1. Hetiopormar. Colonies forming broad, upright, lobed,
or digitate masses flattened from side to side, of a blue colour. Calices
with (usually) fifteen pseudosepta. The coenenchymal tubules do not
branch, but new tubules are intercalated between those previously
existing. Genus—Heliopora, Pallas. From tropical seas in shallow
water. Famity 2. Hexriorirmar. Colonies forming spheroidal masses,
rarely lobate. Calices with twelve pseudosepta. Coenenchymal tubules
more or less regularly hexagonal. Coenenchymal tubes branch dicho-
tomously. Genera—Heliolites, Dana. From the Lower and Upper Silurian,
and the Devonian. Plasmopora, M. Edw. and Haime. Silurian. Propora,
M. Edw. and Haime. Upper Silurian. Lyellia, Edw. and Haime. Upper
Silurian, Famiiy 3. Taecmar. Colonies forming laminar expansions.

THE ANTHOZOA 37

Calices with few, not more than nine, irregular pseudosepta. Coenenchymal

tubules small, numerous, polygonal. Genus—Thecia, M. Edw. and Haime.
From the Wenlock limestone. Fammy 4. CHarretmar. Corallum
massive, consisting of long, prismatic, closely contiguous corallites, with
common walls. No coenenchymal tubules. Genus—Chaetetes, Fischer.
From the Carboniferous. The family Monticuliporidae may provisionally
be placed here. For a full account of the fossil so-called tabulate
corals the reader should consult Nicholson’s works (83 and 84).

ZOANTHARIA—SECOND SuB-CLASS OF THE ANTHOZOA.

The Zoantharian zooid is distinguished from the Aleyonarian
zooid by the following characters :—

The tentacles are usually simple, more rarely compound or
foliaceous, either, only six or more than eight in number, and
never provided with lateral pinnules. As a rule each tentacle,
which is always hollow, is placed over an intermesenterial space.
The mesenteries vary very much in number, and in the disposition
of their longitudinal retractor muscles, but these never have the
arrangement characteristic of the Aleyonaria. Each mesentery is
provided with a mesenterial filament, commonly of a trefoil shape
in section, the median lobe richly provided with gland cells and
nematocysts, the two lateral lobes without these structures, but
richly ciliated. The median lobe is derived from the ectoderm,
the lateral lobes from the endoderm. There are commonly two
ciliated grooves in the stomodaeum, named respectively the sulcus
and sulculus; when one only is present it is named the sulcus.
The musculature is highly developed, especially on the mesenteries,
and the histological differentiation of the tissues is greater than in
the Alcyonaria. A skeleton may be absent or present; when
present it is calcareous or horny, but is never in the form of
spicules, as in the Alcyonaria, and is always developed on the
surface of a special layer of ectoderm cells, which never wander
into the mesogloea.

The Zoantharia may be simple or colonial ; among colonial
forms dimorphism is of uncommon occurrence.

It has been shown that in the sub-class Aleyonaria the anatomy
of the zooids, the individual members of which the colonies are
composed, is remarkably constant, and therefore the modes of
budding, and the architecture of the colonies resulting from those
different modes were selected as the primary characters of taxo-
nomic value. It has been possible to show, with greater or less
certainty, that the highly differentiated and complex members of
the higher groups may be derived from a common Cornularia-like
ancestor, and the existence of a number of intermediate forms has
made it possible, in the case of nearly every group, to trace the
probable lines of divergence from the parent stock. In the

38 THE ANTHOZOA

Zoantharia the case is very different. The zooids present great
diversities of anatomical structure, even whilst their external
features show strong superficial resemblance to one another. We
have to deal with a heterogeneous instead of a homogeneous
assemblage of organisms; and in spite of the labours of many
excellent investigators, we are still unprovided with a clue which
shall enable us to trace out the lines of descent of the principal
groups into which the sub-class must be divided. The difficulties
of classification are consequently great, and the arrangement here
adopted must be regarded as wholly provisional, though pains
have been taken to make it as fully as possible representative of
the actual state of our knowledge.

The type form of the Zoantharia is the ordinary sea-anemone,
of which Actinia equina, Linn. (= A. mesembryanthemum, Ellis and
Sol.), the common red anemone of our English coasts, is an excellent
example.

In a common Actinia the zooid is solitary and does not produce
colonies by asexual generation. The animal has the form of a
hollow cylinder, one end of which, the base, is fixed to a rock or
to some other surface of attachment; at the opposite end is the
mouth, surrounded by tentacles, which are arranged in several
circles. The following regions are easily distinguished :—The
peristome, or space between the mouth and the bases of the
tentacles, the column or body wall, and the basal dise. The
mouth is situated in the centre of the peristome. It is elongate
and slit-like, and surrounded by somewhat tumid lips. In the
living animal the middle portion of the slit is commonly kept
closed by apposition of the lips, the two ends being open. The
tentacles are situated on the periphery and margin of the peri-
stome; they are simple, digitiform outgrowths of the peristome,
retractile, hollow, their cavities communicating below with the
intermesenterial spaces of the coelenteron. Each has a small
aperture at its extremity. They are numerous; as many as 192
in adult specimens, subequal in size, arranged in four cycles of 6, 6,
12, 24, 48, 96. They bear a definite relation to the number of
mesenteries (see Fig. XIX. 1). The margin of the peristome is
studded with several, usually twenty-four, coloured vesicles, which
are batteries of nematocysts.

The mouth opens into a tolerably long stomodaeum which,
like the mouth itself, is flattened from side to side. At each end
of the stomodaeum is a longitudinal groove, lined by specialised
ectoderm cells bearing long cilia. One of these grooves is termed
the sulcus, the other the sulculus, but they do not differ in size or
structure, nor is there any means of determining how the names
shall be applied to the two grooves in any individual specimen.
The mesenteries are numerous, corresponding in number to the

me) ANTHOZOA

tentacles. They are arranged in couples,! the members of each
couple being recognisable by the arrangement of their longitudinal
retractor muscles. These are attached to plaited folds of the
mesogloea and form the so-called muscle banners. They are so
disposed that the muscle banners of each mesenterial couple are
vis & vis, with the exception of two mesenterial couples situated

A:

Fie. XIX.

1.—Diagrammatic longitudinal section through an Actinian, Actinauge Richardi, to show the
general anatomy of the zooid. bw, body wall; st, stomodaeum; s, sulcus; p, peristome; mm,
mesenteries ; mf, mesenterial filament. (After Haddon.)

2.—A mesentery of Tealia crassicornis. t, tentacles; g, gonads; 7, Rétteken’s or circular
muscle; si, internal; and se, external stomata; m/f, mesenterial filament; Um, longitudinal
retractor muscle ; pbm, parieto-basilar muscle. (After O. and R. Hertwig.)

3.—Transverse section between two couples of primary mesenteries of Adamsia Rondoletii.
1, 2, 3, 4, and 5, primary, secondary, tertiary, quaternary, and quinary mesenteries. Jm, muscle
banners ; g, gonads. (After O. and R. Hertwig.)

4.—Transverse section through the stomodzal region of Adamsia diaphana. s, sulcus; sl,
sulculus ; dd, the two couples of directive mesenteries, (After O. and R. Hertwig.)

5.—Section through mesenterial filament of Actinia equina. enl, enido-glandular lobe ; cil,
ciliated lobes. The animal had been fed with powdered carmine, the particles of which have
been ingested by the cells lying between the enido-glandular and ciliated lobes, and are repre-
sented by the black masses. (Original.)

at the two ends of the long axis of the stomodaeum. In these,
which are called the directive mesenterial couples, the muscle
banners are turned away from one another.

Mesenteries are complete or incomplete. A complete mesentery
is attached by the upper part of its inner margin to the stomodaeum,
an incomplete mesentery is not. The free edge of each mesentery

1 It is convenient when speaking of the adult arrangement of the mesenteries to
use the word “couple,” when of their developmental sequence to use the word “pair.”
22

4o THE ANTHOZOA

is thickened to form a mesenterial filament ; in complete mesenteries
the filament commences at the stomodaeum, and ends at a short
distance from the insertion of the mesentery on the basal disc ; in
incomplete mesenteries the filament commences some little way —
below the insertion of the mesentery on the peristome, and ends
below in a similar manner. In the upper and lower parts of their
courses the mesenterial filaments are straight, but their middle
portions are thrown into a number of coils, the mesentery itself
being plaited in a corresponding manner. The structure and
histology of a filament differs in different parts of its course. In
the upper part of its length the filament is trefoil-shaped in section
and has the structure shown in Fig. XIX. 5. The central lobe is
the cnido-glandular tract (Nesseldriisenstreif of German authors),
the lateral lobes are the ciliated tracts (Flimmerstreifen). In the
middle of the filament the cnido-glandular lobe disappears, the two
ciliated tracts remaining ; and in the lower portion of the filament
the ciliated tracts disappear, the median enido-glandular lobe re-
appearing and forming the whole of the filament. Acontia are
filamentous offsets from the lower edge of the mesentery, having
the same general histological structure as mesenterial filaments.
They are characteristic of the family Sagartidae.

The gonads are borne on the mesenteries, forming band-like
thickenings on that part of each mesentery which lies internal to the
longitudinal retractor muscles and below the level of the stomodaeum.
Actinia equina is dioecious, as are many other Actinians, but some
members of the group appear to be monoecious.

The radial chambers into which the coelenteron is divided by
the mesenteries communicate with one another, not only by way
of the axial space into which they all open, but also by perforations
in the mesenteries themselves ; these are mesenterial stomata. In
Actinia the stomata are found in the uppermost inner angles of
the complete mesenteries, close beneath the mouth, and are
probably the result of incomplete union of the mesentery with
the stomodaeum. They are known as internal stomata.

In some other Actiniae, e.g. Tealia crassicornis and Actinoloba
dianthus, external stomata are present. These are circular openings
situated in the upper third of each mesentery, nearer to the body
wall than to the peristome, but separated by a space from both.
Those genera which have external stomata also possess a strong
circular muscle band which runs right round the body just beneath
and outside of the outermost circlet of tentacles. This muscle
band, consisting of an axis of mesogloea thrown into folds along
which muscle fibres are arranged, projects into the coelenteron,
and is attached to the body wall by a thin sheet of tissue. It is
known as Rétteken’s muscle.

In Actinia the coelenteron communicates with the exterior by_

THE ANTHOZOA 41

the mouth, and by the pores at the tips of the tentacles. In the
family Sagartidae there are in addition perforations in the lower
third of the body wall called cinclides through which the acontia
are protruded. In S. parasitica each cinclis is placed on the summit
of one of the warty tubercles scattered over that region of the
body. The histology of the Actiniae has been studied with great
care by O. and R. Hertwig (40), to whose work the reader should
refer for details. The general features of the histology have
already been given on p. 9. The general anatomical features of
an Actinian zooid may be studied in Fig. XIX. 1. 2 shows the
structure of a mesentery and the arrangement of its musculature.
3 and 4 show the order and relations of the mesenteries.

The mesenteries are the most important organs of the
Zoantharian zooid, and it is of great importance that their arrange-
ment and order of succession should be thoroughly understood,
since they afford the only characters which have hitherto been
found to be of definite taxonomic value. The arrangement of the
mesenteries in a typical Actinian is shown in Fig. XIX. 4. As
has already been stated, they are arranged in couples, the muscle
banners of each couple are turned towards one another, except in
the two couples of directive mesenteries (dd) whose muscle banners
face outwards. The following points must be noted over and
above the situation of the longitudinal muscles and the position
of the directive mesenteries :—

(a) The mesenteries are arranged in cycles: six couples in the
first cycle, six couples in the second, twelve couples in the third,
twenty-four in the fourth, and so on. Mesenteries of the same
cycle are of the same size and (with the exceptions mentioned
hereafter) were formed at the same time. The mesenteries first
formed, the primaries, are as a rule the largest; the secondaries
are next in size; the tertiaries smaller than the secondaries, and
so forth. The two couples of directive mesenteries belong to the
first cycle.

(b) Any two mesenteries forming a couple belong to the same
cycle, and are therefore of the same size. The two mesenteries
forming a couple are separated by a narrow space, an entocoele ; the
two mesenteries of adjacent couples are separated by a wider space,
an exocoele,

(c) With the exception of the directives the longitudinal
muscles of the mesenteries are always entocoelic, the transverse
muscles exocoelic.

(d) New couples of mesenteries always take their origin in the
exocoeles, never in the entocoeles.

It is common to find six couples of primary mesenteries in the
Zoantharia. So commonly does this number occur that at one
time the Zoantharia were named the Hexactiniae, in opposition to

42 THE ANTHOZOA

the Alcyonarians, called the Octactiniae. It is now known that
the number six is not nearly so constant as was formerly supposed,
and that where it does occur, the mesenteries of the first cycle are
not developed simultaneously nor in the couples which are eventually
established. In fact, the six-rayed symmetry which was supposed
to be so characteristic of the Zoantharia is not a primary but a
secondary feature. The development of the mesenteries in a six-
rayed Actinian may be said to proceed in two stages. Firstly, the
six couples of primary mesenteries are formed, not simultaneously, as
are the eight mesenteries of Alcyonarians, but irregularly, one after

tl lil
Fic. XX ’

1.—Diagram showing the developmental sequence of the mesenteries in Actinia equina,
Sagartia bellis, and Bunodes gemmaceus.

2.—Shows the sequence of mesenterial development in Rhodactis, Haleampa, and Manicina.

83.—Shows the sequence of mesenterial development in Aiptasia diaphana.

In all the figures the numerals 1, 11, 111, ete., denote the order in which the mesenteries make
their appearance. The eight mesenteries first formed, the so-called ‘‘ Edwardsian ” mesenteries,
are drawn in thick lines, those formed subsequently in thin lines. s, sulcus; sl, sulculus.

the other. This first cycle being once established, the mesenterial
couples of each succeeding cycle are formed synchronously, in a
regular manner, in the exocoeles of the cycles previously existing.

The first cycle of six couples is formed differently in different
genera. In Actinia equina, Sagartia bellis, and Bunodes gemmaceus,
the order of succession is as follows :—

At the period when the stomodaeum is established, and the
mouth has taken onan elongate shape two mesenteries are formed,
marked 1, I, in the diagram (Fig. XX. 1). They divide the
coelenteron into a larger sulcular and a smaller sulear chamber.
It will be seen that these mesenteries originate in the neighbour-

THE ANTHOZOA 43

hood of one of the stomodzal grooves, the sulcus, and are placed
right and left of it. The second pair of mesenteries (II, 11) arises
in the larger sulcular chamber, right and left of the sulcular
groove. It appears to become the sulcular directive couple of the
adult. The third pair of mesenteries (III, 111) arises in the smaller
(sulear) of the two original chambers, right and left of the sulcus,
and forms the sulcar directive couple of the adult. A fourth
mesenterial pair (IV, IV) is then formed, one mesentery in each
interspace between the first and second mesenterial pairs. There
is now a stage with eight mesenteries which is for a short time
persistent. The number of mesenteries corresponds with the con-
dition permanent in the Alcyonaria, but the arrangement of the
muscle banners is quite different. The sulcular (11, 11), suleulo-
lateral (Iv, IV), and sulco-lateral (1, 1) mesenteries have the muscle
banners on their sulcar faces ; the sulcar mesenteries (III, 111) have
the muscle banners on their sulcular faces. In the number and
arrangement of the muscles this stage exactly resembles the per-
manent condition in the genus Edwardsia (cf. Fig. XXI. 2).
The six-rayed symmetry is completed by the formation of the
mesenteries (V, V) in the lateral chambers, and (VI, v1) in the
suleo-lateral chambers, and their muscle banners are so disposed
that they form couples respectively with Iv, Iv, and I, I.

In the genera Lhodactis, Manicina (a Madreporarian coral), and
Halcampa, there is an Edwardsia stage of eight mesenteries, but it
is arrived at somewhat differently. The mesenteries second in
order of formation form with the fifth the sulculo-lateral couples of
the adult ; the mesenteries fourth in order of formation form the
sulcular directives of the adult (see Fig. XX. 2).

A third and peculiar mode of arriving at the six-rayed con-
dition is found in Aiptasia diaphana, which will be best understood
by reference to Fig. XX. 3. There is a stage with eight mesen-
teries, but the muscle banners on I, I, are turned in the direction
opposite to what occurs in Edwardsia.

The tentacles, being placed each above an intermesenterial
chamber, conform in the order of their appearance and in relative
size to the succession of the mesenteries. When the six mesen-
terial couples are established, six tentacles, viz. those placed over
the entocoeles, become larger and longer than the six remaining
exocoelic tentacles ; at a later stage their sizes are equalised.

It will readily be understood from this account, that the
Actinian embryo is at first bilaterally symmetrical. A divisional
plane passing through the sulcus and sulculus divides the body
into two equal and symmetrical halves, and this symmetry is pre-
served till the Edwardsia stage with eight mesenteries is reached.
With the development of the fifth and sixth pairs of mesenteries,
a radial arrangement is superimposed on the primitive bilateral

44 THE ANTHOZOA

symmetry, and thenceforward the radial predominates over the
bilateral type, but a trace of the latter always remains in the
laterally compressed stomodaeum and the two couples of directive
mesenteries. This combination of bilateral and radial symmetry
has been called by Boveri (10) a diradial symmetry.

In the genus Edwardsia, on the other hand, the symmetry is
permanently bilateral.

The genus Edwardsia, of which six British species are recognised,
comprises small Actinians which are rounded at the aboral extremity
and live buried in the sand. The body is divisible into three
regions—an upper capitulum, a median scapus, and a lower physa.
The capitulum and physa are retractile within the scapus, which
is usually invested by a friable cuticle. Though there are only
eight mesenteries and therefore eight intermesenterial chambers,
the tentacles exceed eight in number, sixteen to thirty-two are
generally present. A sulcus and a sulculus are both present,
and the arrangement of the muscle banners in the mesenteries has
been referred to (see Fig. XXI. 1 and 2). The development
of Edwardsia is not known, but Boveri observed in a larva in
which all the eight mesenteries were present that only two of
them, namely, those two corresponding to the mesenteries first
developed in Actinia, Bunodes, ete., bore filaments. Thus it
seems probable that they were the first developed in Edwardsia,
and that the succession of mesenteries is the same in this genus
as in the other forms, but that in Edwardsia the development
stops short at the number eight, whilst the bilateral symmetry is
still perfect ; in other forms it proceeds further, and a biradial
hexameral symmetry is produced,

Seeing that most Actinians (Aiptasia is the exception) pass
through an Edwardsia stage, and the development of Edwardsia,
as far as we know it, points to the same sequence of mesenteries
as in Actinia, it is reasonable to conclude that the latter are derived
from an Edwardsia form. This conclusion is strengthened by the
study of the genus Haleampa, a small anemone which, like
Edwardsia, lives buried in the sand, and is divisible into capitulum,
scapus, and physa (Fig. XXI. 3). From twelve to twenty ten-
tacles are present (usually twelve only), and the physa is perforated
by about twenty-four apertures at its apex. In Haleampa chrys-
anthellum there are in the adult six couples of perfect mesenteries,
arranged on the biradial type, and in addition six couples of very
small imperfect mesenteries in the exocoeles. Fig. XXI. 4 is
a section through the stomodeal region, Of the twelve complete
mesenteries six only bear gonads, viz. those which in order of
development are I, 1; Ul, 1; m1, Ut, Below the level of the stomo-
daeum the asulear directives Iv, IV, are provided with filaments
and muscle banners, but the mesenteries V, V, and VI, VI, become

THE ANTHOZOA 45

much reduced, have no filaments and no muscle banners (Vig.
XXI. 5). Thus we find that whilst twelve primary mesenteries
are present, four of these, namely, those which are absent in
Edwardsia, lag behind the others in size and importance.

We are justified, therefore, in regarding the Edwardsiw as
the nearest living representatives of the ancestor of the six-rayed
Actinians.

Fio. XXI.

1.—Edwardsia claparedii, Panc. (After A. Andres.)

2.—Transverse section through the stomodieal region of Hdwardsia, showing the eight mesen-
teries, and the arrangement of the muscle banners. s, sulcus; sl, suleulus.

8.—Haleampa endromitata, Andr. (After A. Andres.)

4.—Transverse section through the stomodieal region of Halcampa, showing twelve couples of
complete primary mesenteries and six couples of minute incomplete mesenteries in the exocoeles.
dm, directive mesenteries.

5.—Transverse section of the same species below the region of the stomodaeum, showing six
fertile mesenteries—1, 1; 11, 11; U1, 11; the sterile sulcular directives rv, tv, bearing filaments,
and the reduced mesenteries, v, v, and vi, v1, of the first cycle,

To the group of six-rayed Actinians we must now add the
large assemblage of forms, both single and colonial, which have
hitherto been classed apart as the Madreporaria or stony corals.
Researches made by various authors in recent years have shown
that the anatomy of a Madreporarian coral, leaving the skeleton
out of the question, is in all essential par ticulars identical with
that of such a form as Actinia equina. H. V. Wilson has further
shown (98) that in the coral Manicina areolata the sequence of the
development of the first six pairs of mesenteries is identical with
that of Rhodactis and Haleampa. Such being the case, it is no

46 THE ANTHOZOA

longer possible to keep the two groups apart in a scheme of
natural classification. They must be considered as belonging to
an order Actiniidea, and as belonging to the same line of descent
from a common Edwardsia-like ancestor. The structure of the
corals will be detailed further on. Besides the biradial six-rayed
Actinians there are forms which, in external characters, bear the
closest resemblance to the ordinary sea-anemones. The resem-
blance extends to their histological characters, yet they differ
considerably in the number and arrangement of their mesenteries.
There is the family of Tealiidae, containing sea-anemones undis-
tinguishable from others in external appearance. Tealia crassicornis
and 7’. tuberculata are common on the British coasts. In these the
tentacles and mesenteries are arranged not in multiples of six but
of five. In T. crassicornis there are ten couples of complete mesen-
teries of equal size, two couples of which are directives. Between
these are ten couples of smaller mesenteries, and again in the
exocoeles between the first and second cycles twenty couples of still
smaller mesenteries (see Fig. XXII. 1).

It seems difficult to connect this arrangement with the six-
rayed type, but the following ingenious suggestion is given by
Boveri :—The complete mesenteries numbered 1 correspond to the
six couples of the first cycle in Actinia. Those numbered 1%, the four
couples which are added to the other six to make up the apparent
first cycle of ten, belong in reality to the second cycle, but are
precociously developed and intruded amongst the first cycle. The
two couples of mesenteries numbered 2 are the remaining members
of the second cycle, and to them are joined the eight couples of
mesenteries numbered 2%, precocious members of the real third
eycle, which, when added to the two couples 2%, make up the ten
couples of the apparent second cycle. And so on for the remaining
cycles.

Boveri's suggestion is not only very ingenious, but is sup-
ported by a peculiar sequence of mesenterial development observed
in an undetermined larva which he suspected to be that of a
Tealia. The reader is referred to his memoir (10) for details.
Accepting his suggestion, we may provisionally consider the
Tealiidae as an offshoot of the six-rayed Actinians.

Polyopis striata has been described by R. Hertwig. It is a
small Actinian from the Challenger Collection, with thirty-six ten-
tacles reduced to stomidia, and is described as having eighteen
couples of mesenteries—six couples complete, of which two couples
are directives, and in each of the sulco-lateral and sulculo-lateral
chambers three couples of incomplete mesenteries, the middle couple
being the longest (Fig. XXII. 2). According to this deserip-
tion we may, with Boveri, derive Polyopis from the normal
biradial type by suppression of the mesenteries in the lateral

THE ANTHOZOA : 47

exocoeles. But Hertwig’s description is inconsistent with his
figures, in which twenty couples of mesenteries are shown, of which
eight couples are complete, and the position of Polyopis must be
considered doubtful for the present.

Sicyonis crassa has sixty-four mesenterial couples—sixteen com-

Fic. XXII.

1.—Diagrammatic transverse section through the stomodzal region of Tealia erassicornis.
1, 1, primary mesenteries ; 1¢, 12, precociously developed mesenteries of the second cycle ; 2, 2,
“ae gg mesenteries of the second cycle ; 24, 24, precociously developed mesenteries of the third
cycle.

2.—A similar section of Polyopis striata. 1,1, mesenterial couples of the first cycle; 2, 2,
mesenterial couples of the second cycle; 3, 3, mesenterial couples of the third cycle; x, x, the
dotted lines represent mesenterial couples figured by Hertwig, but stated in his description to be
absent. Ifthey were present they would complete the second cycle. <All the mesenteries are said
by Hertwig to reach the stomodaeum, but his figure represents the primaries only as complete.
Hence the inner ends of the secondaries and tertiaries have been represented in dotted lines.

3.—A similar section through Sicyonis crassa. Numerals asini1. There are really sixty-four
mesenteries in Sicyonis, but to avoid crowding the figure the number has been halved.

4.—A similar section through Scytophorus striatus. Numerals as in Fig. XXI.; 2, 2, additional
pair of asulco-lateral mesenteries.

5.—Gonactinia prolifera. Numerals as in Fig. XXI.; y, y, two additional mesenterial couples
in the sulculo-lateral chambers.

6.—Oractis diomedeae. Numerals, etc., as in 53; z, 2, additional mesenterial couples in the
transverse chambers.

plete, sixteen incomplete forming the second cycle, and thirty-two
incomplete forming the third cycle. Only the mesenteries of the
third cycle bear gonads (Fig. XXII. 3). Here, Boveri suggests,
the mesenterial couples numbered 1 are the true primaries, to which
the two couples numbered 1%, belonging really to the second cycle,
are added, making an apparent primary cycle of eight couples. The
apparent second cycle of eight couples is made up of the four

48 THE ANTHOZOA

remaining members of the real second cycle 2, to which are
added the four couples 2%, and so forth. The suggestion is in-
genious ; it can hardly be said to be proved, but may be provision-
ally accepted, and the Sicyonidae may be considered as offshoots
of the six-rayed Actinians. The reader will not fail to notice the
resemblance between Tealia, Polyopis, and Sicyonis. They are
clearly more nearly related to one another than the following, and
are offshoots from the fully formed biradial type :—

The genus Peachia has no sulculus, but a large and modified
sulcus with a conspicuous protuberant lip, the conchula. It has
ten couples of mesenteries—six couples are complete, two couples
being directives. They correspond in number and muscular
arrangement to the definitive primary cycle of Actinia, and are
doubtless homologous with them. The four remaining couples
are incomplete, have no filament, and do not bear gonads, but are
very muscular. One couple is found in each sulco-lateral and lateral
chamber, but there are none in the suleulo-lateral chambers.
Peachia, then, is a six-rayed Actinian with two cycles of mesen-
teries, but the sulculo-lateral couples of the second cycle are sup-
pressed.

The Monauleae of Hertwig are represented by the single
species, Scytophorus striatus. It has only one stomodzal groove
(the sulcus), fourteen tentacles, and seven couples of mesenteries
(Fig. XXII. 4).

This may easily be explained by reference to a larval Hal-
‘ campa. The mesenteries are numbered in the order of their
succession in Halcampa, and to the six couples of the primary cycle
two mesenteries are added niarked 2, z, whose muscle banners are
so disposed that they seem to form couples with the ascular
directives. ;

Gonactinia prolifera, a remarkable form found on the coasts of
Norway and recorded from Falmouth, has sixteen tentacles, a
sulcus and sulculus, and sixteen mesenteries (Fig. XXII. 5).
Of these eight are macromesenteries, are complete, and in the
arrangement of their muscles agree with the Edwardsia type.
The eight others are incomplete micromesenteries ; there is a couple
in each sulculo-lateral chamber, their muscle banners vis d vis ; one
micromesentery in each transverse and sulco-lateral chamber, their
muscle banners so disposed that they face the sulco-lateral and
sulculo-lateral macromesenteries and seem to form couples with
them. Only the four lateral macromesenteries bear gonads, and
in immature forms these are the only four which bear filaments.
In this case the derivation from an Edwardsia form is obvious,
and it may also be observed that if the upper members of the two
pairs of mesenteries marked y, y in Fig. XXII. 5 are taken away,
the arrangement and number of mesenteries resembles Scytophorus.

Oractis diomedeae has been described by M‘Murrich (76). It
has a sulcus but no sulculus; eight complete mesenteries are
present, having an Edwardsia arrangement, and all bear gonads
and mesenterial filaments. In addition there are twelve micro-
mesenteries, whose arrangement recalls that observed in Gonactinia,
but there is an additional couple in each of the transverse chambers
(see Fig. XXII. 6).

From the persistence of the Edwardsian mesenteries as
macromesenteries in Gonactinia and Oractis, and from the easy
transition from Gonactinia to Scytophorus, it may be concluded
that these forms have descended from an Edwardsia-like ancestor,
diverging somewhat low down from the line of descent which led
to the Hexactinian type.

All the Zoantharia hitherto considered agree in their funda-
mental histological characters, and in spite of the exceptions
enumerated, it may be stated of them that, after the first cycle of
twelve couples of mesenteries is established, new mesenterial couples
are formed in the exocoeles between the couples already existing.

The remaining groups of the Zoantharia offer greater diffi-
culties. They differ from the Actinian type both in histological
characters and in the disposition and sequence of their mesen-
teries. There are three groups to be considered—the Zoanthidea,
_ the Cerianthidea, and the Antipathidea.
| The Zoanthidea are mostly colonial, more rarely solitary
_ Zoantharia, without a skeleton, but encrusted externally by a coat
of sandy and other adventitious particles. The colonial forms
are united by basal stolons, which, like those of the Alcyonaria,
|

j THE ANTHOZOA 49
|
:
:
}
.
|
:

ee SE ————————ae

contain numerous solenia. The stolons may fuse to form a
membranous expansion, which again may be thickened*to form a
coenenchyme, in which the proximal moieties of the zooids are
imbedded. The external characters of the zooids are Actinia-
like. There are two circles of tentacles—an inner larger and
a smaller outer circle. The large and small tentacles alter-
nate with one another, and those of the one cycle are placed over
the exocoeles, those of the other over the entocoeles, so that there
are as many tentacles as mesenteries. The mesogloea differs
from that of all other Zoantharia in being permeated by canals
_ which are filled with cells of ectodermic origin. There is a sulcus,
but nosulculus. The mesenteries of the Zoanthidea are bilaterally
disposed in a characteristic manner.
There are two kinds of mesenteries—complete macromesen-
_ teries bearing gonads and filaments, and incomplete micromesen-
_ teries devoid of gonads and filaments. There are two couples of
directives with muscle banners turned away from one another.
The sulear directives are macromesenteries, the asulear directives
micromesenteries. Between these, on either side, lie a variable

50 THE ANTHOZOA

number of mesenterial couples, each couple consisting of a macro-
mesentery and a micromesentery, their muscle banners vis & vis.
In the youngest observed stages of Zoanthidea there are six macro-
mesenteries and six micromesenteries, whose disposition is shown
in Fig. XXIII. 3. They are numbered according to the prob-
able order of their development. (M‘Murrich’s (75) account is
followed in preference to that of van Beneden.) It is obvious that
the sequence is the same as that observed in Hexactinian larvae,

Fia. XXIII.

1.—Polythoa, sp. ? showing expanded zooids.

2.—Zoanthus, sp.? growing on a piece of sponge showing retracted zooids springing from
a membranaceous stolon.

8.—Diagram showing the microtypal arrangement of mesenteries in a young Zoanthid.

4.— Diagram showing the macrotypal arrangement. Numerals in 8 and 4 as in Fig.
XXI. In both microtype and macrotype all the mesenteries succeeding the first twelve are
developed in the sulco-lateral exocoeles, shaded in the diagrams. SD, sulcar directive
macromesenteries ; Asd, asulcar directive micromesenteries.

the difference being that the fourth, fifth, and sixth pairs, instead
of completing the cycle of twelve equal and complete mesenteries,
remain incomplete and are micromesenteries. There is no doubt
that the micromesenteries 4, 4, are homologous with the sulcular
directives of Edwardsia or Actinia, but their arrested develop-
ment as well as the absence of a sulculus suggests that the
Zoanthidea have branched off from a parent form common to the
Edwardsiidea and themselves, and are not descended from an
Edwardsia form, as are the groups hitherto considered. Be this
as it may, the subsequent development is peculiar. New mesen-

THE ANTHOZOA 51

teries are formed only in the sulco-lateral exocoeles. They are
formed in couples, each couple comprising a macromesentery and a
micromesentery, in such wise that the former is always nearest
the sulcar directives. The resulting arrangement is shown in Fig.
XXIV. It will be observed that five of the original six pairs of
mesenteries are pushed up towards the asulcar surface and there
form an asulcar group, characterised by the fact that in the lateral
members of the group the macromesenteries are nearest to the
asulcar directives. Some members of the Zoanthidea show a slight
modification of this arrangement, in that the mesenteries 6, 6,
forming couples with 1, 1, are macromesenteries. Such a modified

MICROTYPE MACROTYPE

Fic. XXIV.

Diagram of the final arrangement of
the mesenteries in the Zoantheae. The
left of the figure shows the microtypal,
the right the macrotypal arrangement.
Numerals as in Fig. XXIII. 3 and 4.
The five mesenterial pairs, 1, 1; 2,254, 4;
5, 5; 6, 6, occupy the asulcar aspect of the
zooid, and it is seen that in this region the
macromesentery of each couple is furthest
from the sulear directives. In the re-
maining sulcar region the macromesentery
of each couple is nearest the sulear direc-
tives.

arrangement is known as the macrotype, the normal arrangement
being called the microtype. The difference is made use of for
purposes of classification.

The Cerianthidea form a limited group, comprising the genera
Cerianthus, Bathyanthus, and Saccanthus. Cerianthus is a solitary
Zoantharian, living imbedded in the sand. Its basal extremity
is rounded, and provided with a terminal pore. The column is
elongated, cylindrical, smooth, protected by a non-adherent case
formed of a felt-work of nematocysts containing grains of sand
and other bodies. The peristome is large, provided with two
circlets of tentacles—marginal and labial (Fig. XXV. 1). There
is a single ciliated groove in the stomodaeum, which is apparently
not the sulcus but the suleulus. The mesenteries are numerous,
and all but the very short pair on the side furthest from the
ciliated groove are complete. The musculature of the mesenteries

52 THE ANTHOZOA

is weak, the longitudinal muscles being less developed than the
transverse, and there are no muscle banners. Carlgren (14) has
shown that the longitudinal muscles are always found on the same
face in each mesentery, namely, on the face turned away from the
ciliated groove. In Edwardsia the opposite is the case, and it
is concluded that the ciliated groove of Cerianthus does not

Fic. XXV,

1.—Cerianthus solitarius, Rapp.

2.—Transverse section through the stomodval region of Cerianthus, showing the sulculus, s,
and the arrangement of the mesenteries. (After O. and R. Hertwig.)

8.—Portion of a mesentery of Cerianthus membranaceus, showing the transverse muscles,
tm, the filament f. The Acontia-like threads, th, borne by the upper edge of the mesentery,
and g, the gonads. (After O. and R. Hertwig.)

4.—Section through the peristome of Cerianthus membranaceus, showing the longitudinal
ectodermic muscles, M; ec, ectoderm; mg, mesogloea; en, endoderm. (After O. and R,
Hertwig.)

5.—Oral aspect of a young Arachnactis brachiolata, the larva of a Cerianthus, with seven
tentacles. (After E. van Beneden.)

6.—Transverse section through the stomodeal region of an older larva. The numerals
indicate the order of development of the mesenteries. (After Boveri, slightly altered.)

correspond with that of Edwardsia, but is the sulculus, the sulcus
being absent.

The pelagic larva shown from the oral surface in Fig. XXYV.
5 is known as Arachnactis brachiolata. It is the young form of
an undetermined species of Cerianthus. Fig. XXYV. 6 is a trans-
verse section through the stomodeal region of an older Jarva. It
has nine tentacles—one small, median, and, according to Carlgren’s
orientation, ascular ; six large and lateral; two of unequal size,
but smaller than the lateral tentacles, occupy the sulcar region.
The section shows that these correspond to as many intermesen-

THE ANTHOZOA 53

terial spaces, and that, in addition, there is a median intermesen-
terial space on the sulcar side as yet unprovided with a tentacle.
The intermesenterial spaces are formed by ten mesenteries, whose
developmental sequence is expressed by the numbers 1, 1; 2, 2;
3, 3; 4,4; 5,5. Thus the larval Cerianthus passes through a stage
with eight mesenteries, and these are developed in the same
sequence as the first eight mesenteries of Haleampa and Rhodactis.
But in the absence of muscle banners it can hardly be called
an Edwardsia stage. The further course of development differs
from anything else that has been described. New mesenteries are
always developed in the sulcar chamber between the previously
existing sulear mesenteries. Thus 5, 5, are developed between
4, 4; 6, 6, will be developed between 5, 5, and so on. It
results that Cerianthus is strictly bilaterally symmetrical, and
that the members of a mesenterial pair are not contiguous, but
are to be found on opposite sides of the stomodaeum. As the
sequence of the first four pairs of mesenteries is identical with
that of Haleampa, etc., it has been held by Boveri and M‘Murrich
that the Cerianthidae are derived from an Edwardsian stock. But
the presence of longitudinal parietal ectodermic muscles must be
held to separate the Cerianthidae from the Edwardsia stock, and,
as in the case of the Zoantheae, they must be regarded as having
diverged from a common ancestor of all the Zoantharia.

The Antipathidea form a well-defined group, whose relation-
ships are very obscure. The type form, <Antipathes dichotoma,
forms arborescent colonies, consisting of numerous zooids arranged
in a single series along one surface of a branched horny axis.
The axis is enclosed by the soft tissues, and is surrounded by a
special epithelium, which in all probability is of ectodermic origin.
Only the number and arrangement of the mesenteries will be con-
sidered in this place, further details being postponed. In the Anti-
patharian zooid the peristome forms a prominent oral cone, on the
summit of which the mouth is placed. It is surrounded by six
tentacles, usually simple and non-retractile, but branched and
retractile in the family Dendrobrachiidae. The stomodaeum is
strongly compressed, and the zooids are so arranged on the axis
that the long axis of the stomodaeum is at right angles to the axis
of the colony. An ill-defined sulcus and a sulculus are present,
and the tentacles corresponding to the sulear and sulcular inter-
mesenterial chambers are longer than the rest. In most of the
genera there are ten mesenteries, which do not bear muscle
banners. The genus Leiopathes is an exception, having twelve
mesenteries. Where ten mesenteries are present, they have the
arrangement shown in Fig. XXVI. 2.

The sulcar and asulcar mesenterial pairs are short; the sulco-
lateral and sulculo-lateral pairs are somewhat longer, but the

54 THE ANTHOZOA

lateral mesenteries which correspond with the long axis of the
colony are very long, and are the only mesenteries which bear
gonads. They are conveniently distinguished as the reproductive
mesenteries. The development of the Antipathidea is unknown,
and it is therefore impossible to say what is the sequence of the
mesenteries ; but it seems probable, from a comparative study
of the existing genera, that the sequence conforms to the
Edwardsio-Actinian type. The tentacles are placed over the sulcar

Fic. XXVI.

1.—Portion of a colony of Antipathes dichotoma.

2,.—Transverse section through the oral cone of Antipathella subpinnata. ss, sulcus sl,
sulculus ; g, gonads.

8.—Transverse section through the upper part of the oral cone of Antipathella minor. The
numerals indicate the probable order of succession of the mesenteries.

4.—A section somewhat lower down from the same specimen, Only three pairs of mesen-
teries are present.

5.—Section through the oral cone of Leiopathes glaberrima. Six pairs of mesenteries are
present, their probable order of succession being indicated by the numerals.

and suleular chambers, and over the four chambers adjacent to the
reproductive mesenteries. In Antipathella minor ten mesenteries
are present in the oral cone, but lower down four of them disappear,
leaving six mesenteries only, which, as Fig. XX VI. 3 and 4 show,
are the sulcar and sulcular pairs and the reproductive mesenteries.
Assuming that the more persistent mesenteries are the oldest,
and that the great reproductive mesenteries correspond in order of
appearance, as they do in position, to the mesenteries 1, 1, in the
Actinian larva, we may number the two remaining pairs 2, 2,

———

THE ANTHOZOA 55

3, 3, and we get a form with six mesenteries whose sequence
corresponds to the sequence of the first six mesenteries in Actinia
equina. But we can go no further. If the mesenteries marked
4, 4, in 3 were found to be developed before those marked 5, 5,
we should get an eight-rayed stage similar in all respects to the
Edwardsia stage in Actinia, except for the absence of muscle
banners.

Leiopathes glaberrima has twelve mesenteries in the oral cone.
Below the level of the stomodaeum only six are present. Study
of serial sections shows that the mesenteries die out in the following
order :—Firstly, those marked 6, 6, in Fig. XX VI. 5; secondly,
those marked 5, 5; thirdly, those marked 4, 4. It will be observed
that the additional pair of mesenteries is the first to disappear,
and that the pair which is presumably fourth in order of develop-
ment outstays the pair which was presumably developed fifth.
In the absence of further evidence it may be conjectured that the
first four pairs of mesenteries are formed in the Antipatharia in
the same sequence as in the case of Actinia, and that therefore
an Edwardsia stage of development may be assumed. It would
follow that the normal number of ten, characteristic of the
Antipatharia, is arrived at by the development of a single mesentery
in each sulco-lateral chamber; and where twelve mesenteries are
present, as in Leiopathes, an additional mesentery is formed on
each side between the sulco-lateral and reproductive mesenteries,
the arrangement of the last two pairs differing from that in
Actinia equina.

It may be concluded that the existing Zoantharia are derived
from a bilateral ancestral form which was provided with no more
than eight mesenteries. In this form there was probably no sulcus
and no sulculus, and muscle banners were absent. It was, therefore,
antecedent to the Edwardsia form, and probably enough was the
common ancestor of the Alcyonaria and Zoantharia. From this
parent form the Cerianthidea, the Zoanthidea, the Antipathidea, and
the Edwardsiidea diverged. From the Edwardsiidea may be derived
all the other recent Zoantharia. The Oractidae, Gonactinidae, and
Monaulidae appear to have diverged early from the Edwardsian
stem, which was continued into the Actinian series which, from its
disguised bilateral symmetry, may be called the Cryptoparamera.
This gave rise to two main branches: (1) Forms with a stony
skeleton, the Scleractineae, equivalent to the Madreporaria of
previous authors, and (2) the Malacactineae, equivalent to the
Actiniaria of previous authors. From the Malacactineae the
aberrant families of the Polyopidae, Sicyonidae, and Tealiidae were
derived. These relationships are expressed in the following
table :—

23

56 THE ANTHOZOA

Pro-Edwardsiae.

Zoanthidea. Antipathidea.
Cerianthidea.
Edwardsiidea.
Gonactinidae:
Oractidae’
Monaulidae:

Cryptoparamera.

Scleractiniae. Malatactiniae.

Sicyonidae. Polyopidae.

Tealiidae.

Whether or no the pro-Edwardsiae were developed from a
cruciform, i.e. a four-rayed ancestor, is a matter of conjecture.
The Rugosa, a heterogeneous group of Palaeozoic corals, are some-
times known as the Tetracoralla because of the characteristic
quadripartite symmetry which they exhibit. In such a form as
Stauria there are four principal septa, placed at right angles to
one another, and several secondary septa arranged in four systems,
those in each system inclining towards a primary septum. <A
different arrangement of the secondary septa obtains in such forms
as Streptelasma, but the quadripartite symmetry is again con-
spicuous. It is tempting to suppose that the four principal septa
stood between four primary mesenteries, which were homologous
with the two pairs first developed in recent Zoantharia. This
would indicate a quadripartite ancestor for the Zoantharia, possibly
for all the Anthozoa. But in the present state of our knowledge
such inferences must be received with caution. The most that can
be said, is that microscopic examination of palaeozoic corals shows
that their skeletons are built up .on the same plan as those of
recent corals, and that it may legitimately be inferred that the
correspondence in structure of the hard parts is evidence of a
correspondence in the structure of the soft tissues which gave rise
to them. The work of Pratz (104), von Koch (102), Quelch (86),
and Ogilvie (103) has resulted in the breaking up of the old group
of the Rugosa, many members of which are now included amongst
families to which recent Scleractineae belong.

The Zoantharia may be classified as follows :—

:
1
4
'

THE ANTHOZOA 57

GRADE I.—PARAMERA.

The primitive bilateral symmetry of the zooid is retained, or at most
is partially obscured by the secondary development of mesenteries in a
limited number of the primary intermesenterial chambers.

OrpeER 1. Cerianthidea.

Solitary Zoantharia paramera without a skeleton. The mesenteries
are numerous, arranged symmetrically in pairs, each member of a pair on
opposite sides of the stomodaeum, The mesenteries devoid of muscle
banners. A sulculus present but no sulcus. Musculature chiefly in the
form of longitudinal ectodermal muscles supported by processes of the
mesogloea of the column.

FaMILy CERIANTHIDAE, Genera—Cerianthus, Dell. Chiaje; Bathy-
anthus, Andres ; Saccanthus, M. Edw.

OrperR 2. Antipathidea.

Colonial Zoantharia paramera with a spinose, horny, usually branch-
ing axial skeleton on which the zooids are seated. Six tentacles, of which
two corresponding to the ends of the long axis of the stomodaeum are
usually larger than the others. Six primary mesenteries always present ;
in most forms four others are developed, one in each sulco-lateral and
sulculo-lateral chamber, making ten. The two mesenteries at right angles
to the long axis of the stomodaeum are greatly developed, and alone bear
gonads. Muscle banners absent.

Famity 1. ANTIPATHIDAE, The individual zooids have six simple
non-retractile tentacles, which may be radiately arranged or in two rows
of three each. Axis spinose and with a central canal. Ten mesenteries
are present. Sus-Fammiy—CirRHIPATHINAE. ‘The zooids are radiately
arranged on all sides of the axis. Genus—Cvtrrhipathes, Blainville. Sus-
Famity—ANTIPATHINAE, The zooids are borne in linear series on one
side of the axis. The transverse axis of the zooid tends to be elongated
in the direction of the long axis of the stem and branches. Genera—
Antipathes, Pallas; Stichopathes, Brook ; Antipathella, Brook ; Aphanipathes,
Brook ; Tylopathes, Brook ; Pteropathes, Brook; Parantipathes, Brook.
Sus-FamMity—ScHIzopaTHINAE. Zooids much elongated in the trans-
verse axis. On either side the two chambers adjacent to the reproductive
mesenteries are separated by a partition from the rest of the zooid, which
thus appears to be divided into three parts—two reproductive and one
gastral. Each division bears two tentacles. Genera—ASchizopathes, Brook ;
Bathypathes, Brook ; Taxipathes, Brook ; Cladopathes, Brook. The last-
named genus has only six mesenteries.

Note.—The Schizopathinae have been described by Brook as dimorphic,
but there is no division of labour accompanied by structural differentia-
tion amongst the zooids, and therefore there is no dimorphism. The
zooids are all alike ; each zooid is greatly modified in connection with the
greatly developed gonadial mesenteries, but there is no division into

58 THE ANTHOZOA

sterile and fertile, gastrozooids and gonozooids. It is easy to trace the
steps which have led to the specialised Schizopathinae. Antipathes is a
nearly radial form, the reproductive mesenteries but little longer than the
others, and the zooid is scarcely elongated in the transverse axis. In
Parantipathes the reproductive mesenteries are very long, the zooid is
much elongated in the transverse axis, and the two pairs of tentacles
belonging to the paragonadial chambers are shifted away from the
oral cone. The formation of incomplete septa dividing the para-
gonadial chambers from the remainder completes the Schizopathine
condition.

Famity 2. LeEIopatHIDAE. Twelve mesenteries are present in the oral
cone. Genus—Leiopathes, Gray. Famity 3. DENDROBRACHIIDAE. Axis
formed by several longitudinal lamellae arranged round a central rod ;
no central canal. Tentacles retractile, pinnate. Genus—Dendrobrachia,
Brook.

OrvER 3. Zoanthidea.

Zoantharia paramera, mostly colonial, rarely solitary. Without a
skeleton, but often encrusted by sand. A sulcus is present, but no
suleulus. Mesenteries numerous, of two kinds, fertile macromesenteries
and sterile micromesenteries. The sulcar directives are macromesenteries ;
the asulcar directives are micromesenteries. In the remaining mesenteries
each macromesentery forms a couple with a micromesentery (one couple
excepted in Macrotypa), their well-developed retractor muscles being
visa vis. After the first twelve mesenteries are established, new mesen-
teries are formed only in the sulco-lateral chambers. Mesogloea permeated
by ectodermic canals.

Famity 1. Zoanrumar. Division 1. Microtypa. The sixth primary
mesenteries are micromesenteries. Genera—Zoanthus, Cuvier ; Mam-
milifera, Lesueur ; Corticifera, Lesueur. Division 2. Macrotypa. The
sixth primary mesenteries are macromesenteries. Genera—Epizoanthus,
Verrill ; Palythoa, Lam.

Famity 2. SpHENOPIDAE. Solitary Zoantheae with rounded aboral
extremity. Genus—Sphenopus, Steenstrup.

Orver 4. Edwardsiidea.

Free solitary Zoantharia paramera with eight mesenteries and sixteen
to thirty-two tentacles. Body divided into capitulum, scapus, and physa.
Without a skeleton. Sulcus and sulculus present. Retractor muscles of
mesenteries well developed, placed on the asulcar aspect of the sulcar
directives, on the sulear aspect of the remaining mesenteries.

Genus—Edwardsia, Quatrefages.

Orper 5. Proactiniae.

Zoantharia paramera in which a variable number of mesenteries is
added to the eight Edwardsian mesenteries. The bilateral symmetry of
the Edwardsia form is retained. No skeleton,

= =_— .—_ —s

THE ANTHOZOA 59

Famity 1. Gonacrinipar. Sulcus and suleulus present. Eight
Edwardsian macromesenteries and eight micromesenteries. The sulcar
and sulcular macromesenteries are sterile, the four remaining macro-
mesenteries are fertile, and form couples with four micromesenteries. Of
the four remaining micromesenteries there is a couple in each sulculo-lateral
chamber. Genus—Gonactinia, Sars ; Gonactinia prolifera reproduces itself
asexually by strobilisation, Famimy 2. Oractipar. No sulculus.
Mesenteries as in Gonactinia, with an additional couple of micromesenteries
in the transverse chambers. Genus—Oractis, M‘Murrich. Famiy 3.
Monaviipar. Sulculus absent. Fourteen tentacles and fourteen complete
mesenteries arranged as in Gonactinia, but the sulculo-laterals are absent.
Genus—Scytophorus, Hertwig.

GRADE II—CRYPTOPARAMERA.

Zoantharia in which the primary bilateral symmetry is obscured by
radial development of the second and succeeding cycles of mesenteries.

OrperR 6. Actiniidea.

Colonial or solitary Zoantharia cryptoparamera, with or without a
skeleton, Sulcus and sulculus both present (with rare exceptions).
Mesenteries arranged in cycles. Lach cycle consisting usually of twelve
couples of equal size. Typically a couple of new mesenteries is formed
in each exocoele formed by previously existing cycles. The muscle
banners of the sulcar and sulcular directive mesenteries are turned away
from one another ; in all other couples they are vis @ vis. Tentacles equal
in number to the mesenteries, one over each endocoele and exocoele,

Sus-Orper 1. Matacacriniar. Solitary Actiniidea or very rarely
forming colonies. Without a skeleton.

Group A. HExXAcTINIAE.

Famity 1. Inyanturpar. Free Malacactiniae, not adhering by a basal
disc. Aboral end of body rounded. Susp-Famrnby—HaAtcamprnak.
Tentacles twelve. Mesenteries twenty-four—six couples complete, six
couples incomplete. Genus—Halcampa, Gosse. Sup-Faminy—ILyan-
THINAE. Genus—ZIlyanthus, Forbes. Sup-Faminy—Peracuiinar. Ten-
tacles twelve. Mesenteries twenty; six primary couples complete, fertile ;
four secondary couples, the sulculo-lateral couples being absent. A single
conchula present. Genus—Peachia, Gosse.

Famity 2. ActiIntipDAE. Malacactiniae with an adherent basal disc.
Tentacles simple, uniform, arranged in cycles on periphery of peristome,
one tentacle over each exocoele and endocoele. Sus-FAamtLy—ANTHEINAL.
Marginal tubercles present. No circular muscle. No acontia. Genera—
Actinia, Browne ; Anemonia, Risso; Comactis, M. Edw. Sus-Famrby—
SAGARTINAE. Circular muscle present. Acontia present. Primary
mesenteries alone complete, and are sterile. Division A. Circular muscle
endodermal. Genus—Actinoloba, Blainville. Division B. Circular muscle

60 THE ANTHOZOA

mesogloeal. Genera—~Sagartia, Gosse ; Calliactis, Verrill ; Cereus, Oken ;
Phellia, Gosse ; Chondractinia, Liitken ; Hormathia, Gosse ; Chitonactis,
Fischer ; Actinauge, Verrill ; Adamsia, Forbes; Aiptasia, Gosse. Sus-
Famity—Bvunopinag. Circular muscle present. No acontia. The column
covered with tubercles. Genera—Bunodes, Gosse ; Aulactinia, Verrill ;
Cladactis, Panceri. Sup-Faminy—Paracrinrnan. Circular muscle
mesogloeal. Many perfect mesenteries, Genera—Paractis, Andres ;

5
Paractinta, Andres; Paranthus, Andres. Sus-Fammby—ANTHEOMOR-

Fic. XXVII.

1.—Adamsia Rondeletii, D. Ch. (=Sagartia parasitica).
2, 2a, 2b, Bunodes rigidus, Andres. 8.—Octophellia timida, Andres.
4.—Corynactis viridis, Allman.

PHINAE. No circular muscle. Complete mesenteries numerous. All
the mesenteries fertile. _Genus—Antheomorphe, Hertwig. Famity 3.
CORALLIMORPHIDAR. Tentacles arranged in a double corona, one corona
marginal and principal, the other intermediate and accessory. Mesenteries
slightly differentiated, all fertile. No circular muscle, Sus-Fammy—
CORALLIMORPHINAE. Genus—Corallimorphus, Moseley. Subp-FamMILy—
CoRYNACTINAE. Genera—Corynactis, Allmann; Capnea, Forbes. (In
Corynactis viridis the bases of the zooids are confluent, so that they
adhere to form a colony.) Sus-Famity—Discosomrnar. Genus—
Discosoma, Leuck. Famity 4, Liponemipar. Marginal tentacles trans-

THE ANTHOZOA 61

formed by retrograde formation into short tubes or stomidia. Genera—
Polystomidium, Hertwig ; Polysiphonia, Hertwig. Faminry 5. AMPHIAN-
THIDAE. Malacactineae embracing by their bases stems of Gorgonidae ;
with shortened sagittal and elongated transverse axis, circular muscle
mesogloeal. Primary septa alone complete, but sterile. Genera—
Stephanactis, Hertwig; Amphianthus, Hertwig; Gephyra, von Koch.
(Possibly the genus Savaglia with twenty-four tentacles and twenty-four
mesenteries must be placed here. It was formerly classed among the
Antipatheae.) Famity 6. Denpractipar. Some or all of the tentacles
ramified or foliaceous. Susp-Faminy—Ruopacrinag, Genera—Rhodactis,
M. Edw. ; Taractea, Andres. Sus-Famity—PHYMANTHINAE. Genera—
Phymanthus, M. Edw. ; Triactis, Klunz. Sup-Famirny—PHyYLLActTINAg,
Genus—Phyllactis, M. Edw. Sups-Famiry—CramBactinagr. Genus—
Crambactis, Haeckel. Sus-FAmMILy—CrYPTODENDRINAE. Genus—Crypto-
dendron, Klunz. Famity 7. THALASSIANTHIDAE. The disc is covered
with peculiar appendages, which are not tentacles, and are termed fronds.
Each frond is villose, pinnate, or tubercular. Sup-Fammy—THALASSIAN-
THINAE. Genera—Thalassianthus, Leuck ; Actineria, Blainv. ; Megalactis,
Ehrb.; Actinodendron, Ehrb. Sus-FAMILyY—SarcoPHIANTHINAE. Genus—
Sarcophianthus, Lesson.

Group B.

Malacactineae in which precocious development of the secondary and
succeeding cycles of mesenteries obscures the hexameral arrangement.

Famity 1. TEALmDAE. Genus—Tealia, Gosse. Faminy 2. Potyo-
PIDAE. Genus—Polyopis, Hertwig. Famity 3. Sicyontpar. Genus—
Sicyonis, Hertwig.

For the characters of these three families, see p. 46.

The classification of the Malacactineae given above must be
considered provisional. As far as possible the lines laid down by
Hertwig (41) have been followed, as his classification is based on
anatomical characters. But the anatomy of many forms is still
undescribed, and where anatomical characters are wanting the
arrangement of Andres (1) has been followed.

SuB-ORDER 2. SCLERACTINIAE (= MADREPORARIA). Actinideae
provided with a calcareous skeleton secreted by cells called calico-
blasts, which actually are or represent the basal ectoderm.

The anatomy of the soft parts of any Scleractinian resembles,
in essential points, that of an Actinia. There are complete and
incomplete mesenteries arranged in cycles, the sequence of numbers
being usually 12, 12, 24, 48, etc., as in Hexactiniae. Usually two
couples of directive mesenteries are present, but in a few forms
(Mussa, Lophohelia, and Euphyllia) there are no directives. For
a detailed account of the anatomy of such corals as have been
studied, the reader is referred to the works of von Koch (51, 57,

62 THE ANTHOZOA 4

58, 59, 63); von Heider (38) ; Fowler (23-26); Bourne (6 and 7) ;
and Ogilvie (103).

The relations of the zooid to the skeleton may be studied in
Fig. XXVIII. which represents a diagrammatic longitudinal section
through a Turbinolid coral. A quadrant is cut out on the left
side to further display the anatomy. In the skeleton of a typical
solitary coral—the common Devonshire cup-coral, Caryophyllia
Smithii, is a good example—the following parts are to be dis-

Fic. XXVIII.

Diagram illustrating the relation of the soft tissues to the corallum in a solitary aporose
coral. St, stomodaenm ; Sul, sulcus ; M, mesenteries ; Th, theca; S, septa; Col, columella; Ep,
epitheca ; P, edge-zone.
tinguished :—(1) The basal plate, between the zooid and the
surface of attachment. (2) The septa, radial calcareous laminae
reaching from the periphery to near or quite to the centre of the
ealycle. (3) The theca or wall, which, in many corals, is not an
independent structure, but is formed by the conjoined peripheral
ends of the septa. (4) The columella, a structure which occupies
the axis of the corallite, and may be solid or trabeculate. If it
arises from the base, it is termed essential; if formed by the
union of trabeculae from the septa, it is termed unessential. (5)
The costae, longitudinal ribs or rows of spines on the outer surface
of the theca. True costae always correspond to the septa, and
are in fact the peripheral ends of the latter. (6) Zpitheca, an
offset of the basal plate which surrounds the base of the theca in
a ring-like manner. (7) Pali, laminae which extend upwards from

a

THE ANTHOZOA 63

the bottom of the calycle and project between the inner edges of
certain septa and the columella. In addition to these parts, other
structures are found in the skeletons of certain corals. Dissepi-
ments are oblique calcareous partitions stretching from septum to
septum, and closing the interseptal loculi below (see Fig. XX XI.
2). The whole system of dissepiments in any given calyx is often
called endotheca. Synapticula are calcareous bars uniting adjacent
septa (Fig. XXXI. 3). Tabulae are stout horizontal partitions
traversing the whole space within the calycle.

Though the skeleton or corallum of the Scleractiniae appears
to lie within the zooid, it is morphologically external to it, as is
best shown by its developmental history, which has been studied
by G. von Koch in Astroides calicularis (55) and in Caryophyllia

Fic. XXIX.

Radial section of the larva of Astroides calicularis, which has fixed itself on a piece of cork.
ec, ectoderm ; en, endoderm; mg, mesogloea; mm, mesenteries; S, septum; B, basal plate.
formed of ellipsoids of carbonate of lime secreted by the basal ectoderm ; ep, epitheca. (After
G. von Koch.)

cyathus (105), and by H. V. Wilson in Manicina areolata (98).
The larvae of Astroides are at first ciliated and free-swimming,
and do not acquire a corallum until they fix themselves. The
first trace of the corallum appears as a ring-shaped plate of cal-
careous tissue situated between the basal ectoderm and the surface
of attachment. It is composed of calcium carbonate in the form
of numerous spheroidal masses of concentric structure, each mass
built up of numerous rhombic crystals. Von Koch states definitely
that the calcareous nodules are formed as a secretion product of
the ectoderm, and he gives figures which fully bear out his assertion
(Fig. XXIX.) Wilson, as far as he has traced the development of
the corallum in Manicina, confirms von Koch’s statement. Von
Heider, however, holds that the calcareous crystals are formed
within ectodermic cells, as are the spicules of Aleyonaria, but his
proofs are not satisfactory... The further development of the
corallum is effected by the completion and increase in size of the

1 Since this was written, Dr. Maria M. Ogilvie has expressed herself strongly in
favour of von Heider’s opinion. The subject requires reinvestigation, but it must be
said that Ogilvie’s evidence is not strong enough to overthrow the positive embryo-
logical observations of von Koch and H. V. Wilson. (The writer has since shown

that von Koch’s views are correct and that no true spicules, formed within cells,
occur in the Scleractiniae.—Quart. Jour. Micr. Sci. vol. xli.)

64 THE ANTHOZOA

basal plate, and the formation of the septa. The first traces
of the septa are radially disposed folds of endoderm, on the
basal disc, one fold in each endocoele and exocoele. As twelve
mesenteries are present, twelve septa are formed simultaneously.
Beneath each fold the ectoderm becomes detached from the surface
of the basal plate, and is folded inwards conformably with the
endoderm, so that ridges composed of all three layers project
into the coelenteron. Between the limbs of the ectodermic folds
calcareous nodules are formed, and these fuse together to form
the septa. The septa soon fuse with the basal plate, and each
primary septum becomes forked at its peripheral end, so that,
when viewed from above, it has the shape of a Y. At a later
stage the septa form relatively high but thin radial plates, over
each of which the three layers—ectoderm, mesogloea, endoderm—
are folded. They increase in size, their peripheral ends branch,
and eventually the branches of adjacent septa unite with one
another to form a porous theca. At the same time their central
ends unite and form a trabecular columella. Whilst the septa are
being formed, and are becoming united to form a theca, a secretion
of carbonate of lime from the wall of the young zooid, at the
point where basal dise passes into body wall, gives rise to a thin
lamina which is continuous with the basal plate. This is the
epitheca ; at first it is separate from the theca, but at a subsequent
period is united to it by processes. Of the twelve septa first
formed six, viz. the exocoelic septa, grow faster than the others,
and thus there appear to be two cycles of alternately larger and
smaller septa, six in each cycle. From the foregoing account, it
is evident that the corallum is formed from the basal ectoderm,
and that it is, as it were, pushed up from below into the cavity of the
zooid, each part of the corallum carrying before it the three layers
—ectoderm, mesogloea, and endoderm. Further, it is evident that
the theca in Astroides is not an independent structure, but is
formed by the coalescence of the peripheral ends of the septa. In
Caryophyllia, however, the theca is formed independently of the
septa. The development explains a feature present in many
Scleractiniae. The soft tissues of the zooid extend outside the
theca, and invest it to a greater or less extent. This extrathecal
extension of the soft tissues is shown in Fig. XXVIII. P. A
section through this region shows that the extrathecal soft tissues
enclose a cavity which is a part of the coelenteron, and, like the
latter, is divided into chambers by partitions, which are the
peripheral parts of the mesenteries. The extrathecal soft tissues
will be called the edge-zone. The extent of the edge-zone and its
relations to the intracalicular part of the zooid will easily be
understood after a study of Fig. XXVIII., and a transverse section
through the upper part of a zooid is shown in Fig. XXXI. 1,

;
|
|

THE ANTHOZOA 65

from which it will be seen that the theca appears to cut the
mesenteries in two. It will also be noticed that, in an aporose
coral such as is shown in Fig. XXX. 2 and 4, the only com-
munication between the cavities in the edge-zone and the remainder
of the intermesenterial spaces is by way of the lip of the calicle,

en .
: ry gg 3 t .

\ oe At Be ae ‘ 7 ,

om | R. 6.

Fie. XXX.

1.—Astroides calicularis. Schematic longitudinal section through a zooid and a bud, show-
ing the relations of the soft tissues to the corallum. In this, and in figures 2 and 4, the
thick black line represents the soft tissues, the corallum is gray. The sections are much
simplified, the mesenteries, etc., being omitted. S, stomodaeum; T, tentacles; C, coenosare ;
Col, columella.

2.—A similar section through a single zooid and bud of Stylophora digitata. On the left
of the figure the coenosarc is seen to be supported on echinulations of the coenenchyme.

3.—A diagram illustrating the process of asexual reproduction by unequal division.

4.—Schematic longitudinal section through three coralities of Lophohelia prolifera. In the
upper part of the figure the larger zooid is seen to be in connection with the smaller zooid
formed from it by division both internally and externally by way of the edge-zone. The lowest
zooid has lost all organic connection with the other members. P, edge-zone ; other letters as in 1.

5.—A section through a dividing calicle of Mussa, showing the union of two septa in
the plane of division and the origin of new septa at right angles to them.

6.—Side view of the upper part of the specimen shown in 5. (4 original, the rest after
G. von Koch.)

but in the perforate coral the theca is permeated by numerous
anastomosing canals lined by endoderm, which place the cavities
of the edge-zone in communication with the central coelenteron.

According as these canals are absent or present, the Sclerac-
tiniae are classified as Aporosa or Perforata, and the anatomical
character in question is sufficiently definite to afford a basis of
classification. There are, however, some corals which cannot be
placed in either of these groups.

66 THE ANTHOZOA

There are both solitary and colonial Scleractiniae, and both
solitary and colonial forms occur in the two groups Aporosa and
Perforata. The colonial forms are produced by asexual reproduc-
tion either by gemmation or division, the resulting individuals
remaining in connection with one another. Several of the solitary
Scleractiniae reproduce themselves asexually by discontinuous
budding or division. Blastotrochus nutriz, a member of the family
Flabellidae, produces lateral buds on the theca, which after a
time drop off, and a new bud may be formed from the scar
of the old one. Some species of Flabellum reproduce them-
selves asexually by transverse fission. Lhodopsommia parallela
and &. socialis, perforate corals, bear marginal and lateral buds
which may detach themselves. In the genus Fungia, the discoid
free adult forms are asexually produced from an attached parent
stock termed the trophozooid, and the adult individuals may
multiply themselves by transverse fission.

In the formation of colonies by asexual reproduction, the
distinction between gemmation and division must be borne in
mind. In the former case the young zooid, with its corallum,
arises wholly outside of the cavity of the calyx of the parent
zooid, and the component parts of the young corallum, theca,
septa, columella, etc., are formed anew in every individual pro-
duced. In division a constriction divides a zooid into two or
more equal or unequal parts, and the component parts of the two
(or more) coralla so produced are severally derived from the
corresponding parts of the dividing corallum.

Gemmation in the colonial Aporosa and Perforata always
proceeds from the soft tissues which clothe the outside of the
theca, i.e. from the edge-zone or its derivatives. In the case of an
aporose coral a bud is formed on the edge-zone, and develops into a
new zooid with its corallum. The cavity of the latter does not
communicate directly with the cavity of the parent, but organic
connection between parent and offspring is effected by means of
the edge-zone. As growth proceeds, and parent and bud become
separated further from one another, the sheet of soft tissues
connecting the two loses the characters shown in Fig. XXXI.
1, A, the peripheral continuations of the mesenteries are no
longer present, and there is found instead a sheet of tissue resting
upon projecting spines of the corallum, between which run canals
lined by endoderm, the last-named serving as the means of com-
munication between zooid and zooid (see Fig. XXXI. 1, B).
Such a sheet of soft tissue, devoid of the peripheral continuations
of the mesenteries, and bridging over the spaces between the
zooids, may be called the coenosarc. The layer of calicoblasts
on the lower surface of the coenosare gives rise to a secondary
deposit of carbonate of lime, which more or less fills up the spaces

,

THE ANTHOZOA 67

between individual corallites, and is distinguished as coenenchyme.
The individual corallites may be wholly immersed in coenenchyme,
in which case the whole of the soft tissues connecting the zooids

have the character of coenosarc; or, as in Galaxea, Fig. XXXIII.

5, the corallites may be only partially immersed in coenenchyme,

‘in which case the soft tissues on the outside of the projecting

Fie. XXXI.

1.—Diagrammatic transverse section through two quarters of a zooid of Amphihelia ramea.
A, through the theca in the region of the tentacles, showing the peripheral ends of the mesen-
teries in the cavity of the perisarc. B, below the stomodaeum, showing the external canals
between the body wall and corallum. Ectoderm blocked black and white, corallum shaded.
(After G. H. Fowler.)

(0 an section through a corallite of Puphyllia, showing the dissepiments, DS.
riginal.

Bo iairagnimatis representation of the relations of septa, SS; mesenteries, MM; costae,
CC; and body wall, P, in Stephanophyllia formosissima, ina small cube cut out of the Base of
the zooid; RT, radial trabeculae; SN, synapticula. Ectoderm blocked black and white;
corallum dotted. (After Fowler.)

4.—Part of a section through a corallite of Euphyllia, showing the formation of the theca,
Th, from the peripheral ends of the septa; SS, dissepiments. (Original.)

distal moieties of the corallites have the characters of edge-zone,
whilst the spaces between the corallites are covered with coenosare,
the latter shading imperceptibly into the former. For a full
description of these relations the reader is referred to Fowler’s
Memoirs (22-26).

Budding takes place in an analogous manner in perforate corals,
but the relations between edge-zone and coelenteron, referred to

68 THE ANTHOZOA

above, induce modifications in the process. The canal system
which permeates the porous theca becomes much extended, and, as
it extends, calcareous tissue is deposited between the network of
canals, so that the theca appears to be enormously thickened.
But the mesenteries do not share in this extension, and so the
edge-zone proper—that is to say, the soft tissue which is external to
the calyx, and is supported on prolongations of the mesenteries—

Fic. XXXII.

1.—Section through a branchlet of Madrepora, sp.? showing an axial zooid with septa, the
surrounding coenenchyme, and two buds, B, b’.

2.—Diagram of a longitudinal section of Madrepora durvillei, showing the perforations
in the stomodaeum leading into canals hollowed out in the mesenteries. M, mesentery; S,
septum; Th, theca; Ps, perisarc.

8.—Diagram of the various forms and conditions of the mesenteries in a zooid of Madrepora
durvillei. The mesenteries numbered 1, 1; 2, 2; 3, 3, and bear no filament and are simple; the
remainder are modified, and bear filaments below the level of the stomodaeum.,

4.—Diagram of a transverse section of a zooid of the same species. Ps, perisare.

5.—Transverse section of a modified mesentery of M. dwrvillei, passing through two arms
of the stomodzal canal. The thickened endoderm of the modified mesentery is clearly seen.

(1 original ; the rest after Fowler.)

becomes limited to the neighbourhood of the mouth of the calyx.
The rest of the coral is clothed with a coenosare in which no traces
of the mesenteries are discoverable. From this coenosare buds
arise which grow into zooids whose cavities are permanently con-
nected with the cavities of the other zooids composing the colony
by means of the system of canals just spoken of, as well as by
the canals of the coenosare (see Fig. XXX. 1, and Fig. XXXII.
1, 4). It is clear that in the perforate corals the spongy tissue

THE ANTHOZOA 69

in which the calicles lie is in its origin a thecal structure,
and that it is impossible to say where the theca of one corallite
ends and that of another begins. In aporose corals, on the other
hand, the theca is a well-defined structure, and the calcareous
tissue in which the corallites are imbedded is a secondary deposit
of entirely different origin.

In the formation of colonies by division a distinction must be
made between equal and unequal division, though the two processes
merge into one another. The process of equal division is well
illustrated by Mussa (Fig. XXX. 5, 6). The zooid, previously
subcircular in section, becomes elongated in the direction of the
long axis of the mouth, and at the same time the tentacles, mesen-
teries, and septa increase in number. A constriction, at right
angles to the long axis of the mouth, involves first the mouth,
then the peristome, and finally the calyx itself, so that the zooid
and its corallite, previously single, becomes divided into two. The
part played by the septa and theca will be best understood by a
study of Fig. XXX. 5. After division the two corallites grow
upwards ; at first their zooids are united by a bridge of soft tissue
or edge-zone, but as they grow further and further apart this con-
tinuity is broken, each corallite is clothed externally to a greater
or less extent by its proper edge-zone, and, as the interseptal loculi
become closed below by dissepiments, all organic connection
between the two zooids is eventually lost, though the corallites
remain attached to one another. There are, however, forms
not far removed from Mussa in which the corallites are closely
apposed after division, the continuity of the edge-zone is not
broken, and growth leads to the formation of a coenosare which,
as in the case of colonies produced by gemmation, gives rise to a
coenenchyme filling up the spaces between the corallites. The
complex Meandrine corals are produced by incomplete division
which involves the mouth, and to some extent the peristome, but
does not extend to the calyx. Repetition of this incomplete
division gives rise to long Mzandrine channels, each containing
numerous zooid mouths.

Unequal division may be studied in Lophohelia prolifera and
allied forms, and the process is illustrated in Fig. XXX. 3, 4.
Instead of the whole calyx undergoing division, a small portion of
it is constricted off to form a young zooid which, in its earliest
stage, looks like a bud on the margin of the calyx. Reference to
3 shows, however, that the process of unequal division differs
from that of gemmation in that, in the former, the theca, septa,
and columella of the young zooid are directly formed from corre-
sponding structures in the parent. As growth proceeds, the smaller
or daughter calyx becomes more and more separate from the
larger or parent calyx, and eventually it looks like a lateral bud

70 THE ANTHOZOA

borne by the latter, the cavities of the two being still in free com-
munication below. As a rule, this communication is eventually.
cut off by a secondary deposit of calcareous tissue, and then the
two zooids are united only by their confluent edge-zones. But as
growth proceeds this union also is broken, and the zooids in the
older parts of the colony are isolated, and have no organic connec-
tion with one another (see Fig. XXX. 4).

The classification here adopted is based upon Martin Duncan’s
revision of the Madreporaria (79), with the modifications intro-
duced by Quelch (86). It cannot be pretended that it is a natural
or a satisfactory classification, yet it is the best which can be
offered in the present state of our knowledge. Other systems
have been proposed, but they have not stood the test of criticism,
and have been ephemeral. Milne-Edwards and Haime divided
the Scleractineae into five sections—Aporosa, Perforata, Rugosa,
Tabulata, and Tubulosa. The two last named have long since
been broken up and their families distributed, some among the
Alcyonaria, others among the Aporosa. The Rugosa, also termed
the Tetracoralla, held their ground for a long time; but it has
been shown that the structure of the skeleton of the rugose corals
does not differ from that of recent corals, and the tetrameral
symmetry, which so many of them exhibit, is to be considered of
less importance, since it has been shown that a hexameral symmetry
is by no means characteristic of recent corals. Moreover, the
tetrameral symmetry is an inconstant feature in Rugosa. The
discovery of Moseleya latistellata, «a reef coral from Wednesday
Island, Torres Straits, leaves no doubt as to the close relationship
of the Astraeidae to the Cyathophyllidae. *Moseleya is a compound
coral with polygonal calicles, a thin epitheca, a rudimentary theca,
and the cavity of the calicle is filled up nearly to the margin by
tabulae separated by an abundant dissepimental endotheca. The
septa in adult calicles are numerous and give no indication of
a hexameral arrangement, but in young calicles a tetrameral
symmetry is distinctly visible, owing to the cruciate arrangement
of four larger septa. Moseleya shows decided affinities on the
one hand to a typical Astraeid, such as Prionastraea ; on the other
hand toa Cyathophyllid, such as Cyathophyllum regium, and it cannot
be doubted that the Cyathophyllidae and the forms allied to them
can no longer be classified apart as Rugosa, but must be placed
along with or close to the Astraeidae.

There is some doubt as to the distinctness of the sections
Aporosa and Perforata of M. Edwards and Haime. The anatomical
features on which the division is based have been referred to above,
but there are corals ranked among the Aporosa in which the theca
is perforated by a few canals, and amongst the Perforata there is
every grade between trabeculate and spongiose theca and septa

THE ANTHOZOA 71

and a comparatively compact structure, the septa being aporose
and the theca and coenenchyme traversed by a sparse canal system.
The distinctness of the section Fungacea may also be called into
question. The characteristic of the group is the presence of
synapticula, which are transverse calcareous bars uniting adjacent
septa. But such transverse bars are to be found in many corals
not included among the Fungacea, e.g. in Stephanophyllia formosissima,
Mich., and in some other Eupsammidae. Fungia, the type of the
Fungacea, is regarded by some authors as a perforate coral; but
it must not be forgotten that in its young state it is aporose,
and has all the characters of a typical Turbinolid, synapticula
being developed only as
the lip of the calyx ex-
pands to form the char-
acteristic fungiform disc.
This indicates a close re-
lationship between the
Fungidae and the Tur-
binolidae. On the other
hand, the Plesioporitidae,
now included amongst
the Fungacea, are per-
forate corals, and if the
divisions Aporosa and
Perforata are of any
value, they are clearly
out of place. The fol-
lowing classification, n4{itiaphuium hemgoum, Goldtuss, from the Devonian
then, is to be regarded Palaeontologie).

as provisional and likely

to be supplanted at no distant date by an entirely new arrange-
ment. The sub-section Scleractiniae is very rich in genera and
species; Duncan enumerates 343 genera, without taking account
of the Rugosa. In this place only the more important and familiar
genera will be cited, and the reader in search of further details
is referred to, Duncan (19), Quelch (86), Moseley (82), and to the
British Museum Catalogues of Madreporaria by Brook (12) and
Bernard (13).

[Since this article was written and in proof the work of Dr.
Maria Ogilvie has been published. As a result of an extensive
study of the microscopic characters of recent and extinct corals
she divides the Scleractineae into two sections—Zaphrentoidea or
Haplophracta and Cyathophylloidea or Pollaplophracta. The first
section is divided into the sub-sections Coenenchymata (families
Poritidae, Madreporidae, Pocilloporidae, Oculinidae) and Murocorallia
(families Zaphrentidae, Turbinolidae, Amphiastraeidae, Stylinidae).

24

Fig. XXXII.

72 THE ANTHOZOA

The second section is divided into the sub-sections Septocorallia
(families Cyathophyllidae, Astraeidae, Fungidae) and Spinocorallia
(family Hupsammidae). Whilst recognising the value and sug-
gestiveness of Miss Ogilvie’s work, her classification cannot be
adopted here, for it is open to serious criticism. The grounds for
removing the Eupsammidae from the other Perforata seem to
be scarcely sufficient. The sub-section Coenenchymata appears
artificial. The Murocorallia are defined as corals which have
a well-built theca, whose fibrous elements are set in a direction at
right angles to those of the septa. In this group are included the
Turbinolidae, and it \is more than doubtful whether it can be
predicated of all members of this group that they have a theca
separate from the septa. Von Koch has recently shown (102)
that the theca is an independent structure in the larval Caryophyllia,
but as growth proceeds the distinction between the two becomes
lost, and a section through an adult Caryophyllia shows that the
septa are thickened and in contact at their peripheral ends, thus
forming, in the upper moiety of the calyx, at any rate, a so-called
pseudotheca, such as would characterise the group Septocorallia.
For a discussion of the question as to the relations between theca
and septa the reader should refer to the excellent memoir of von
Koch (102).]
Section 1. Aporosa.

Simple or colonial Scleractineae with solid theca and septa not
perforated by canals; the theca may be epithecate.
In colonial forms the zooids may be separate
from one another, or, if in organic continuity,
their cavities communicate only by means of
superficial canals in the coenosare. Famity Il.
ZAPHRENTIDAE. Solitary palaeozoic Scleractineae
with an epithecal wall. Septa well developed,
arranged pinnately with regard to four principal
septa, the main- and counter-septa. Tabulae
present. Vesicular endotheca absent or scanty. No
columella. Genera — Zaphrentis, Rafinesque and
Clifford; Amplexus, M. Edw. and H.; Omphyma,
Raf. and Clifford; Streptelasma, Hall (Figs.
XXXIV. and XXXV.), etc. Famiry 2. TuRBINO-
LIDAE. Solitary Scleractineae, or forming colonies
by gemmation from the bases of the parent zooids

Fic. XXXIV. or from a stolon-like expansion from the base of
Streptelasma cornicutum, the parent zooid. Septa radial not pinnate. In-
Hall, from thelowerSilurian terseptal loculi open to the base, 7.e. without tabulae
Size (trem zittel). Nat. oy dissepiments. Sup-Famity 1. FLABELLINAE.

The wall is epithecate. Genera — Flabellum,
Lesson ; Duncania, Pourtales; Schizocyathus, Pourtales; Rhizotrochus,
M. Edw. and H.; Plewrocyathus, Moseley ; Desmophyllwm, Ehrenb. ;

THE ANTHOZOA 73

Blastotrochus, M. Edw. and H. ; Placocyathus, M. Edw. The existence
of an epithecate wall, with which is correlated the absence of a perisare
is sufficient to separate the Flabellinae from other Turbinolidae, and
the same feature brings them into relationship with the Zaphrentidae.
Further researches may lead to the inclusion of several forms now classed
as Turbinolinae amongst the Flabellinae. Flabellwm variabile and
Placotrochus laevis reproduce themselves asexually by a process of strobil-
isation, and Blastotrochus nutrix gives rise to lateral deciduous buds
(see Semper, 91). Sus-Faminy 2. TURBINOLINAE. Group 1. SIMPLICES.
The zooids solitary. Genera—Smilotrochus, M. Edw. and H.; Turbinolia,
M. Edw. and H. ; Trochocyathus, M. Edw. and H.; Caryophyllia, Lamarck ;
Stephanotrochus, Moseley. Group 2. GrEMMANTES. Colonies are formed
by gemmation from the bases of the parent zooids. Genera—Coenocyathus,
M. Edw. (Recent and Tertiary) ; Gemmulatrochus, Duncan. Group 3.
ReptanTes. Buds are formed from a stolon-like expansion of the base

eae Cog

Fic. XXXV.
Schematic representation of the calyx
Ms of a Zaphrentid seen from below. c, main

1 septum; g, counter-septum; ff, trans-
t verse septa; cq, chief quadrant; gy,

counter quadrant. The numbers indicate
4; + the order in which the septa are formed.

In the chief quadrants the secondary
10 septa radiate from the chief septum, the
9 most recently formed lying nearest to the

transverse septa, the oldest nearest to the
§ chief septum. In the counter quadrants
the secondary septa radiate from the
‘ transverse septa, and the most recently
G q. Ny formed are nearest to the counter septum.

of the parent zooid. Genera—Polycyathus, Duncan; Agelecyathus,
Duncan. Famity 3. OcuLinmwar. Aporosa, forming irregular branching
colonies. Asexual multiplication by mural budding. The walls of the
corallites increase in thickness exogenously, the thickening (coenenchyme)
being due to the activity of the calicoblastic layer of the edge-zone. Genera
—WNeohelia, Moseley ; Lophohelia, M. Edw. and H. ; Oculina, M. Edw. and
H. ; Stylophora, M. Edw. and H. ; Madracis, M. Edw. and H. Famity 4.
PociLLoporIpAk. Colonial Aporosa with tabulae. Two larger septa,
axial and abaxial, are present, and traces of ten smaller septa. Genera—
Pocillopora, Lamarck ; Seriatopora, Lamarck. For an account of these
two genera see Moseley (81) and Fowler (25). In Seriatopora subulata
there are twelve mesenteries, of which those corresponding to 1, 1; 2,
2; 3,3; 4,4 in Rhodactis and Manicina (see above, p. 43) are longer
than the others, but only 1, 1 bear filaments. Faminy 5. ASTRAEIDAE.
Simple or colonial Aporosa with dissepimental or vesicular endotheca ;
with or without tabulae. A solid intercalicular coenenchyme rarely
developed. An epitheca surrounds the base of massive and Mieandroid

74 THE ANTHOZOA

forms, but only surrounds individual corallites in simple or branching
forms. Sus-Famity 1. ASTRAEINAE. <A. Simplices. Genera—Trocho-
smilia, M. Edw. and H.; Placosmilia, M. Edw. and H., ete. B. Reptantes.
Genera—Cylicia, M. Edw. and H.; Astrangia, M. Edw. and H, C.,
Gemmantes. Genera—Cladocora, M. Edw. and H.; Goniocora, M.

Edw. and H. (Trias, Lias, and Oolite), ete. D. Caespitosae. Genera
Eusmilia, M. Edw. and H.; Mussa, Oken. FE. Confluentes. Genera

Fic. XXXVI.

1.—Vertical section through the corallum of Caryophyllia Smithii, showing the theca,
septa, pali, columella.

2.—View of an individual of the same species from above.

I ‘ patagonich , a specimen viewed from the side.

} rhe same f 0

.—Enlarged v wn calicle, with surrounding calicles, from a branchlet of
Madrepora. The perforate character of the theca and coenenchyme is well seen.

6.—View of a portion of a colony of Galaxea lapei t, showing corallites projecting
i in abund pe l i

—Euphyllia, M. Edw. and H. ; Diploria, M. Edw. and H. ; Maniectna,
Ehrb. ; Meandrina, Lam. ; Coeloria, M. Edw. and H. ; Hydnophora, M.
Edw. and H. F. Agglomeratae fissiparantes. Genera—VFavia, Oken ;
Goniastrea, M. Edw. and H. G. Agglomeratae gemmantes. Genera—
Heliastrea, M. Edw. and H.; Echinopora, Dana; Galazea, Oken ;
Isastrea, M. Edw. and H. (Trias, Cretaceous, Miocene); Merulina, Ehrb.
For a fuller account of the Astraeinae see Duncan (19). Ogilvie (84a) has
recently broken up the Astracinae, separating the Eusmilinae, M. Edw.
and H., from them and placing the Trochosmiliacea, M. Edw. and H.,

—-=- —

‘THE ANTHOZOA 75

among the Turbinolidae ; Euphyllia and Rhipidogyra and their allies
form a new family, the Amphiastraeidae ; Galaxea is placed.in Klunzinger’s
family, the Stylinidae. See her paper, pp. 159-167. Sus-Famity 2.
CYATHOPHYLLINAE. Solitary and colonial Astraeidae, never Mzandroid.
Tabulae and vesicular endotheca present. Genera
—Moseleya, Quelch ; Cyathophyllum, Goldfuss
(Devonian, Carboniferous, and Permian). Sus-
Faminy 3. Sraurtnar. The septa show a
marked tetrameral arrangement. No columella.
Genus—Stauria, M. Edw. (Upper Silurian).
Sus-Famity 4. CysTIPHYLLIDAE. Septa rudi-
mentary ; calicles filled with vesicular endotheca.
Genera—Cystiphyllum, Lonsdale (Silurian and
Devonian) ; Michelinia, de Kon. (Carboniferous).
In the sub-family Goniophyllinae the calyx is
provided with a movable calcareous operculum.
Genera—Goniophyllum, M. Edw. and H. (Silur-
ian) ; the operculum formed of four paired pieces,
attached to the four sides of the lip of the calyx Fic, XXXVII.

and reaching with their pointed ends to the — Cualecola sandalina, Lam.,
centre. Rhizophyllum, Lindstrom (Silurian) ; Xoo" {ve (trom Bitte. .
the operculum simple, semicircular, with a

median ridge on its inner face, and numerous striae parallel to it.
Calceola, Lam.; the operculum thick with a stout median septum
and numerous feebly developed secondary septa.

Following Quelch the Cystiphyllidae are here placed with the
Astraeidae. Ogilvie, whilst remarking on their affinities with the Astraeidae,
places the Cystiphyllidae in the same group as the Eupsammidae under
the name Spinocorallia, loc. cit. pp. 324, 325.

SECTION 2. FUNGACEA.

Solitary or colonial Scleractiniae. Septa united by synapticula, which
cross the interseptal loculi and perforate the mesenteries,

Famity 1. PLEsIOFUNGIDAE. Colonial or simple Fungacea. Septa
generally solid and imperforate ; united by synapticula. Genera—~Sider-
astrea, Blainv.; Thamnastrea, Lesauvage ; Lophoseris, M. Edw. and H. ;
Agaricia, Lamarck. Faminy 2. Funempar. Simple or colonial Fungacea ;
usually depressed or discoid. Theca more or less synapticulate. Group 1.
Solitary Fungidae. Genera—Fungia, Dana; Diafungia, Duncan; Micra-
bacia, M. Edw. and H. The young form of Fungia is fixed, and either
solitary or colonial, resembling in all its characters a turbinolid, such as
Caryophyllia. The fixed form developed from the ovum is called a tropho-
zooid. The free discoid adult, or anthocyathus is formed by the expansion
of the upper part of the calicle of the trophozooid. When this has
acquired a dise shape, and its septa are united by synapticula, it is detached
from the pedicle (anthocaulus) formed by the rest of the trophozooid, and
is set free as an adult Fungia. Three or four anthocyathi may be formed
in succession from one trophozooid. For details the reader should refer

76 THE ANTHOZOA -

to Stutchbury (93), Semper (91), and Bourne (8). Group 2. Colonial
Fungidae. Genera—Halomitra, Dana; Cryptabacia, M. Edw. and H.;
Herpolitha, Eschholtz. Famitry 3. Cyciosermar. Simple or colonial
Fungacea, in which the wall is not perforated. _Genera—Trochoseris, M,
Edw. and H.; Cyeloseris, M. Edw. and H.; Bathyactis, Moseley ;
Psammoseris, M. Edw. and H. ; Podoseris, Duncan ; Cyathoseris, M. Edw.
and H. (Cretaceous and Eocene) ; Mycedium, Oken ; Leptoseris, M. Edw.
and H.; Stephanaria, Verrill. Famiry 4. ANapactapar, Genus—
Anabacia, VOrb. Famity 5. Piestoporitmar. Septa trabeculate and
perforate. Genera—Leptophyllia, Reuss. (Jurassic and Cretaceous) ; Cyclo-
lites, Lamk. (Jurassic and Cretaceous) ; Meandroseris, Rousseau (Recent).
This classification of the Fungacea can hardly be considered satis-
factory, and requires revision after an extended study of the anatomy
and development of different forms. The characteristic of the group is
the presence of synapticula, but this would lead to the inclusion of the
genus Stephanophyllia, Mich., which has been shown by Fowler (26) to
possess true synapticula, The Fungacea, as above classified, are connected
with the Aporosa, on the one hand, through the Plesiofungidae, and
with the Perforata, on the other hand, through the Plesioporitidae. But
it should not be forgotten that the young Fungia is a typical Aporose
coral, and it is probable that the Fungacea will have to be broken up
into two groups, which will belong respectively to the Aporosa and the
Perforata, the presence of synapticula being a character of insufficient
importance to justify the formation of a section Fungacea.

Secrion 3. PERFORATA.

Scleractiniae with a corallum composed chiefly or wholly of porous
coenenchyma. The coelentera of the zooids composing a colony com-
municate by means of coenenchymal canals.

Famity 1. EvpsaAMMipar. Simple or colonial Perforata; septa in
several cycles ; the principal cycles imperforate. Genera—sStephanophyllia,
Michelin ; Leptopenus, Moseley ; Balanophyllia, 8. Wood ; Eupsammia,
M. Edw. and H.; Heteropsammia, M. Edw. and H. ; Dendrophyllia,
M. Edw. and H. ; Astroides, Blainv. ; Rhodopsammia, Verrill. Fami.y 2.
Mapreporipag£. Colonial Perforata with abundant coenenchyma, scarcely
distinct from walls of corallites. Septa often porous and reduced.
Genera— Madrepora, Linn. ; Turbinaria, Oken; Astraeopora, Blainv. ;
Montipora, Quoy and G.; Anacropora, Ridley. The genus Madrepora
is exceedingly rich in species. For an account of the Madreporidae, see
3rook (12). Famity 3. Porrrmpar. Colonial Perforata with trabeculate
septa. Genera—Porites, M. Edw. and H.; Synarea, Verrill ; Goniopora,
Quoy and G.; Rhodarwa, M. Edw, and H.; Alveopora, Quoy and Gaim.,
ete.

LITERATURE OF THE ANTHOZOA,

1. Andres, A. Fauna u. Flora des Golfes von Neapel, ix. 1884. (Actinien.)
2. Beneden, E. van. Arch. de Biol. x. 1890, p. 485. (Larval Zoantheae. )
3. Jbid. Bull. de l’Acad, Roy. de Belg. (3), xxi. 1891, p. 179. (Arachnactis.)

_
SOHONHD OE

= — _ 1 —
D> Ox i oo i)

se
on

19.

20.

21.

22.
23.

24,
25.
26.
27.
28.
29.
30.
31.
32.
33.
34,
35.
36.
37.
38.
39.

40,

41.

LITERATURE OF THE ANTHOZOA 77

. Blainville. Manuel d’Actinologie. Paris, 1834.

Blochmann and Hilger. Morph. Jahrb. xiii. 1888, p. 385. (Gonactinia.)

. Bourne, G. C. Quart. Jour. Micr. Sci. xxvii. 1887, p. 359. (Fungia.)

Ibid. 'Q. J. M. S. xxviii. 1888, p. 21. (Mussa and Euphyllia.)
Ibid. Trans. Roy. Dubl. Soc. v. 1893, p. 205. (Develpt. of Fungia.)

- Ibid. Phil. Trans. clxxxvi. 1895, p. 455. (Heliopora and Xenia.)
. Boveri, Th. Zeit. Wiss. Zool. xlix. 1890, p. 461. (Develpt. and Phylogeny

of Zoantharia. )

. Brook, G. Challenger Reports, Zool. xxxii. 1889. (Antipatharia.)
. Ibid. Catalogue of Madreporarian Corals in Brit, Museum, vol. i. 1893.

(Madrepora. )

. Bernard, H. M. Cat. Madrep. Corals, Brit. Mus. ii. 1896. (Turbinaria

Astraeopora. )
Carlgren, O. Ofversigt af. K. Vet. Akad. Férhandlingar, 1891-93. (Ed-
wardsia and Ceriantheae.)

- Dana, J. D. United States Exploring Expedition, Zoophytes. Phila-

delphia, 1846.

. Ibid. Corals and Coral Islands. New York, 1872. 2nd Ed. Lond. 1885.
. Dixon, G. F. and Y. Sci. Proc. Roy. Dub. Soe. vi. 1889, p. 310.
. Danielssen, D. C. Report of Norwegian, N. Atlantic Exped. Zool. xix.

1890. (Actinidae.)

Duncan, P. M. Jour, Linn. Soc. xviii. 1885, p. 1. (Classification of
Madreporaria. )

Ehrenberg, C. G. Die Korallthiere des rothen Meeres. Abh. d. k. Akad.
Berlin, 1832.

Ellis, J. The Natural History of many curious and uncommon Zoophytes.
Lond. 1786.

Erdmann, A. Jenaische Zeitsch. xix. 1886, p. 430. (Zoantheae.)

Fowler, G. H. (The Anatomy of the Madreporaria, i.) Quart. Jour. Micr.
Sci. xxv. 1885, p. 577.

Ibid. Q. J. M.S. xxvii. 1887, ‘p. 1.

Ibid. Q.J. M.S. xxviii. 1888, p. 1.

Ibid. Q. J. M.S. xxviii. 1888, p. 413.

Ibid. Q. J. M.S. xxx. 1890, p. 405.

Genth. Z. Wiss. Zool. xvii. 1867, p. 429. (Solenocaulon.)

Gosse, P. H, Actinologia britannica. Lond. 1860.

Haacke,W. Jenaische Zeitschrift, xiii. 1879, p. 269. (Blastology of Corals. )

Hiickel, E. Arabische Korallen. Berlin, 1875.

Haddon, A. C. Sci. Proc. Roy. Dublin Soe. y. 1886, p. 1. (Halcampa.)

Ibid. Sci. Trans. Roy. Dublin Soe. iv. 1888, p. 297. (Revision of Actiniae. )

Ibid. Sci. Proc. Roy. Dub. Soc. 1892, p. 127. (Larval Euphyliia.)

Haime, J. : Ann. Sci. Nat. (4), i. 1854, p. 341. (Cerianthus. )

Heider, A. von. Sitz. d. Kais Akad. Wien. ]xxv. 1877.

Ibid. Sitz. d. Kais. Akad. Wien. lxxix. 1879. (Cerianthus.)

Ibid. Zeit. Wiss. Zool. xliv. 1886, p. 152. (Astroides, Dendrophyllia. )

Herdman, W. A. Proc. Roy. Phys. Soc. Edinb. viii. 1885, p. 31. (Sar-
codictyon. )

Hertwig, O. and &. Die Actinien, Jena, 1879 ; also Jenaische Zeitschrift, xiii.
1879, p. 457.

Hertwig, R. Challenger Reports, Zool. vi. 1882 ; and xxvi. 1888. (Malak-
actiniae, Zoantheae.)

49,
50.

LITERATURE OF THE ANTHOZOA

. Hickson, S. J. Quart. Jour. Micr. Sci. xxiii. 1883, p. 556. (Tubipora.)

. Ibid. Phil. Trans, clxxiv. 1883, p. 693. (Sulcus of Alcyonarians. )

. Ibid. Proc. Roy. Soc. No. 243, 1886, p. 322.

. Ibid. Trans. Zool. Soc. Lond. xiii. 1894, p. 325. (Alcyonaria stolonifera.)
. Ibid. Quart. Jour. Micr. Sci. xxxvii. 1895, p. 343. (Aleyonium.)

. Johnston, G. A History of British Zoophytes, Edinb. 1838. 2nd Edition,

1847.

. Jungersen, H. F. E. Zeit. Wiss. Zool. xlvii. 1888, p. 626. (Develpt. of

Pennatula. )
Klunzinger, C. B. Die Korallthiere des Rothes Meeres. Berlin, 1877.
Koch, G. von. Anat. der Orgelkoralle. (Tubipora.) Jena, 1874.

50a. Ibid. Festschrift fiir Gegenbauer, 1896.
50b. Ibid. Mitth. Zool. Stat. Neapel. xii. 1897, p. 754.

. Ibid. Jenaische Zeitschr. xi. 1877, p. 375. (Stylophora.)

. Ibid. Morph. Jahrb. iv. 1878, p. 74. (Gephyra Dohrnii.)

. Ibid. Morph. Jahrb. v. 1880, p. 355. (Cerianthus, Zoanthus.)

. Ibid. Morph. Jahrb. vii. 1882, p. 467. (Telesto.)

. Ibid, Mitt. Zool. Stat. Neapel. iii. 1882, p. 281. (Develpt. of Astroides.)
. Ibid. Palaeontographica, xxix. 1883, p. 329. (Asexual Reproduction in

Recent and Fossil Corals. )

. Ibid. Morph. Jahrb. xii. p. 154, (Relations of hard to soft parts in Madre-

poraria. )

. Ibid. Morph. Jahrb. xiv. 1888, p. 330. (Flabellum.)

. Ibid. Morph. Jahrb. xv. 1889, p. 10. (Caryophyllia.)

. Ibid. Zool. Jahrb. v. 1891, p. 76. (Sympodium.)

. Ibid. Fauna und Flora des Golfes des Neapels, xv. 1887. (Die Gorgoniden.)
. Ibid. Festschrift der teknischen Hochschule zu Darmstadt, 1886. (Anti-

pathes. )

. Ibid. Kleinere Mittheilungen iiber Anthozoen, Morph. Jahrb. xv., xvi., xvii.

XViii.

. Kolliker, A. von. Icones histiologicae. Leipzic, 1863.

. Ibid. Die Pennatuliden, Abhand. d. Leuckenb. Naturf. Gesell. vii.

. Ibid. Challenger Reports, Zoology, i., Pennatulids, 1880.

. Koren and Danielssen. Nye Alcyonider, etc.° Bergen, 1883.

. Ibid. Norske Nordhavs-Expedition, Aleyonida, 1887.

. Kowalevsky and Marion. Ann. Mus. Hist. Nat. Marseille, i. 1888. (Develpt.

of Clavularia.)

. Lacaze-Duthiers, H. de. Hist. Nat. du Corail. Paris, 1864.
. Ibid. Arch. Zool. Expér. et gén. i. 1872 ; and ii. 1873. (Development.)
- Lamouroux. Exposition Méthodique des genres de l’ordre des Polypiers,

Paris, 1821.

. M‘Murrich, J. P. Johns Hopkins Univ. Cire. viii.!No. 70. (Edwardsia

stage in Hexactinians. )

. Ibid. Journ. Morph. iv. 1891, p. 131. (Cerianthus.)
- Ibid. Journ. Morph. iv. 1891, p. 308. (Succession of Mesenteries in *

Zoantharia.)

. Ibid. Journ. Morph. v. 1892, p. 125. (Phylogeny of Anthozoa.)
. Marshall, A. M. Trans. Roy. Soc. Edinb. xxxii. 1887, p. 140. (Pen-

natulacea.)

. Marshall, A. M., and Fowler, G. H. Trans. Roy. Soc. Edinb. xxiii. 1888,

p. 453.

ADDENDUM TO THE ANTHOZOA 79

79. Milne-Edwards, H., and Haime. Hist. Nat. des Coralliaires, Paris, 1857,
3 vols.

80. Moseley, H. N. Phil. Trans. clxvi. 1876, p. 91. (Heliopora and Sarco-
phytum.)

81. Tbid. Quart. Jour. Micr. Sci. xxii. 1882. (Seriatopora, Pocillopora.)

82. Ibid. Challenger Reports, Zool. ii. 1881. (Deep Sea Corals.)

83. Nicholson, H. A. Palaeozoic Tabulate Corals, Edinb. 1879.

84. Ibid. The Genus Monticulipora, Edinb. 1881.

84a. Ogilvie, M. M. Phil. Trans. elxxxvii. 1896, p. 83.

85. Ortmann, A. Zeit. Wiss. Zool. 1. 1890, p. 278. (Formation of Colonies in
Madreporaria. )

85a. Pratz, E. Palaeontographica, xxix. 1882. (Structure and Relationships of
Extinct Corals.)

86. Quelch, J. J. Challenger Reports, Zool. xvi. 1886. (Reef Corals.)

87. Quoy and Gaimard. Voyage de l’Astrolabe, 1834.

88. Ridley, S. O. Rep. Zool. Collect. H.M.S. Alert, Alcyonaria, p. 356.

89. Sars, M. Fauna littoralis Norvegiae, 1846, p. 28. (Arachnactis.)

90. Schneider and Rotteken. Ann. Mag. Nat. Hist. (4), vii. 1871, p. 437.
(Transl. )

91. Semper, C. Zeit. Wiss. Zool. xxii. 1872, p. 235. (Alternation of Generations
in Corals.)

92. Studer, Th. Monatsb. d. k. Preuss. Akad. Wiss. 1875, p. 668. (Soleno-
caulon.)

93. Stutchbury. Trans. Linn. Soc. 1830, p. 494. (Asexual Reproduction of
Fungia. )

94, Verrill. Amer. Jour. Arts and Sciences, xlv. 1868, p. 415; and numerous
papers in succeeding numbers.

95. Vogt, C. Arch. de Bidlogie, viii. 1888. (Cerianthus.)

96. Wilson, Z. B. Phil. Trans. clxxiv. 1883, p. 723. (Develpt. of Renilla.)

97. Ibid. Mitth. Zool. Stat. Neapel. v. 1884, p. 1. (Mesenterial Filaments of
Alcyonaria.)

98. Wilson, H. V. Journal of Morphology, ii. 1888, p. 191. (Develpt. of
Manicina.)

99. Wright, P. S. Proc. Roy. Phys. Soc. Edinb. ii. 1859, p. 91. (Peachia.)

100. Zbid. Quart. Jour. Micros. Sci. v. 1865, p. 213. (Hartea.)

101. Wright, P. S., and Studer, Th. Challenger Reports, Zoology, xxxi.
(Aleyonaria), 1889.

ADDENDUM.

Since this article was written, the author has studied the structure and
formation of the calcareous skeleton in a number of different genera of
Anthozoa with the view of deciding the question whether the skeleton of
the Scleractiniae is composed of entoplastic spicules as von Heider and
Ogilvie assert, or whether it is an ectoplastic product as described by von
Koch. The results of these investigations may be briefly summed up as
follows :—In all the Alcyonaria except Heliopora the calcareous skeleton
consists of spicules, a “‘spicule” being the entoplastic product of a single
cell or of a coenocyte. The spicule is covered by a sheath of organic
substance, and its axis is traversed by an organic thread or bundle of
threads from which other organic threads radiate outwards and are

80 ADDENDUM TO THE ANTHOZOA

attached to the spicule sheath. The inorganic constituents of the
spicule show a complex, fibro-crystalline structure, the component
crystalline fibres always being oriented in a definite manner with
regard to the organic threads. In Heliopora the skeleton is not spicular
but lamellar, resembling in structure that of the Scleractinian corals. It
is not formed of a number of fused spicules, but is secreted by a special
layer of cells derived from the ectoderm and called calicoblasts. The
calicoblasts are separated from the corallum by a fine membrane. At
intervals in the layer of calicoblasts and lying among them are peculiar
structures which will be called desmocytes. These are wedge-shaped
bodies, with their narrower ends attached to the mesogloea, their broader
ends attached to the corallum. They exhibit a faint but distinct
longitudinal striation, which is not due to the presence of needles of
carbonate of lime. The desmocytes are most abundant in the older parts
of the colony, and are absent or only represented by early stages ot
development in those parts where coral growth is most active. There
can be no doubt that the desmocytes of Heliopora are homologous with
the similar structures in Scleractinian corals, discovered by von Heider
and called by him calicoblasts. After examination of a large number of
Scleractiniae the present writer found that (1) the corallum is everywhere
clothed by a layer of cells either rounded, columnar, or fused together,
which form the true calicoblastic layer ; (2) that the calicoblastic layer is
separated from the corallum by a fine membrane ; (3) that desmocytes (von
Heider’s calicoblasts) occur at widely separated intervals in the calicoblastic
layer, except along the lines of insertion of the mesenteries, where they are
numerous and closely crowded together ; (4) that each desmocyte is the
product of a single cell’; (5) that the striations of the desmocytes are not
due to the presence of spicules of carbonate of lime as von Heider
supposed, since they give none of the optical effects of crystals ; (6) that
desmocytes do not occur in the regions of most active coral growth. The
conclusion arrived at is that the desmocytes, both in Heliopora and the
Scleractiniae, have no share in coral’ formation, but serve, as Fowler
suggested, to attach the soft tissues to the corallum. A study of the
costal spines of Madrepora rosacea showed that the carbonate of lime
secreted by the calicoblasts is deposited in the form of minute crystals on
the far side of the limiting membrane which separates the calicoblasts
from the corallum. These minute crystals are oriented conformably to
the crystalline structure of the previously existing corallum, and eventually
become merged into its structure. Thus von Koch’s view that the corallum
is secreted by the calicoblastic layer derived from the ectoderm is shown
to be correct (see Quart. Jour, Micro. Sct. vol. xli. 1899, p. 449).

INDEX

To names of Classes, Orders, Sub-Orders, and Genera ; to technical terms ; and to
names of Authors discussed in the text.

Acalephae, 2
Acanella, 28
Acanthogorgia, 28
Acanthoisis, 28
Acanthoptilum, 34
Acis, 28

-| Antipathes, 53, 57

Antipathidae, 57
Antipathidea, 53, 57
Antipathinae, 57
Aphanipathes, 57
Aporosa, 65, 72

Briareinae, 25
Briareum, 25
Brook, 57, 71
budding, 16, 67
Bunodes, 42, 60
Bunodinae, 60

acontia, 41 Arachnactis, 52
Actinauge, 60 Aristotle, 2 calamus, 30
Actineria, 61 asexual reproduction in| calcareous skeleton, 12

Actinia, 42, 59
Actinidae, 59

corals, 66
A siphonacea, 29

Calceola, 75
calicoblast, 66

Actiniidea, 46, 59
Actinodendron, 61
Actinoloba, 59
Adamsia, 60
Agaricia, 75
Agassiz, A., 4
Agelecyathus, 73
Aiptasia, 48, 60
Aleyonacea, 19, 23
Alcyonaria, 10
Aleyonidae, 17, 23
Alcyonium, 24 -
Aldrovandus, 2
Alveopora, 76
Ammothea, 25
Amphianthidae, 61
Amphianthus, 61
Amphilaphis, 28
Amplexus, 72
Anabacia, 76
Anabaciadae, 76
Anacropora, 76
Anemonia, 59
Antheinae, 59
Antheomorphe, 60
Antheomorphinae, 60
anthocaulus, 75
anthocyathus, 75
Anthomastus, 24
Anthoptilidae, 34
Anthoptilum, 34
Anthothela, 25
Anthozoa, 2
Antipathella, 54, 57

Astraeidae, 70, 73
Astraeinae, 74
Astraeopora, 76
Astrangia, 74
Astroides, 76

— development of, 63
Audouin, 4
Aulactinia, 60
autozooid, 11, 30
Azifera, 18, 19, 26

axis, of Pennatulids, 30

— development of, 32

Balanophyllia, 76
Barathrobius, 25
basal disc, 38

— plate, 62
Bathyactis, 76
Bathyanthus, 57
Bathygorgia, 28
Bathypathes, 57
Bathyptilum, 34
Bebryce, 28

Belon, 2

Beneden, P. J. van, 4
— E. van, 50, 52
Bernard, 71

bilateral symmetry, 43
biradial symmetry, 44
Blastotrochus, 66, 73
Boccone, 3

Bourne, 22, 62, 76
Boveri, 44, 46, 47
Briareidae, 18, 25

Calliactis, 60
Callisis, 28
Callistephanus, 28
Callozostrinae, 28
Callozostron, 28
Calypterinus, 28
Calyptrophora, 28
Calyptrophorinae, 28
canal system, 68
capitulum, 44
Capnea, 60
Carijoa, 30
Carlgren, 52

Caryophyllia, 62, 63, 72

Cavernularia, 34
Cavernularinae, 34
Cavolini, 4
Ceratoisidinae, 28
Ceratoisis, 28
Cereus, 60
Cerianthidea, 51, 57
Cerianthus, 51, 57
Chaetetes, 37
Chaetetidae, 37
Chironepthya, 25
Chitonactis, 60
Chondractinia, 60
Chrysogorgia, 28

cinclides, 41

Cirrhipathes, 57
Cirrhipathinae, 57
Cladactis, 60
Cladocora, 74
Cladopathes, 57

82

Clavella, 34
Clavularia, 20
cnidoblasts, 9
coelenteron, 5
Coelogorgia, 18, 30
Coelogorgidae, 30
Coeloria, 74
Coenenchymata, 71
coenenchyme, 67
Coenocyathus, 73
coenosarc, 66
Coenothecalia, 19, 35
columella, 62
column, in Zoantharia, 38
Columnaria, 22
Columnariidae, 22
Comactis, 59
conchula, 48
Corallidae, 18, 25
Corallimorphidae, 60
Corallimorphinae, 60
Corallimorphus, 60
Corallium, 25
Cornularia, 20
Cornulariidae, 20
Corticifera, 58
Corynactinae, 60
Corynactis, 60
costae, 62
Crambactinae, 61
Crambactis, 61
Cryptabacia, 76
Cryptodendrinae, 61
Cryptodendron, 61
Cryptoparamera, 59
Cuvier, 4
Cyathophyllidae, 70
Cyathophyllinae, 75
Cyathophylloidea, 71
Cyathophyllum, 70, 75
Cyathoseris, 76
cycles, of mesenteries, 42
Cyclolites, 76
Cycloseridae, 76
Cycloseris, 76
Cylicia, 74
Cystiphyllidae, 75
Cystiphyllum, 75

Dana, 4

Danielssenia, 28

Dasygorgia, 28

Dasygorgidae, 18, 28

Dendractidae, 61

Dendrobrachia, 58

Dendrobrachiidae, 53, 58

Dendrophyllia, 76

Desmophyllum, 72

Desor, 4

development, of Alcyonaria,
13

Diafungia, 75
dimorphism, 11
Diploria, 74
Discosoma, 60
Discosominae, 60
Dissepiments, 63
division, in Scleractinia, 66
dorsum, 7
Drifa, 25
Dubenia, 34
Duncan, 70, 71
Duncania, 72
Duva, 25

Echinopora, 74
ectoderm, 5
edge-zone, 64
Edwardsia, 44, 58
Edwardsiidea, 58
Ehrenberg, 4
Ellis, 4

endoderm, 5
endotheca, 63
entocoele, 41
epitheca, 62
epithelio-muscular cells, 10
Epizoanthus, 58
equal division, 69
Esper, 4
Lugorgia, 28
Eumuricea, 28
Eunepthya, 25
Eunicea, 28
Eunicella, 28
Euphyllia, 74
Eupsammia, 76
Eupsammidae, 71, 76
Eusmilia, 74
exocoele, 41

Favia, 74
Favosites, 22
‘avositidae, 22
Flabellinae, 72
Flabellum, 72, 78
Fowler, 62
Fulla, 25
Fungacea, 71, 75
Fungia, 66, 71, 75
‘uniculina, 34
Funiculinidae, 33, 34

Galaxea, 67, 74
ganglion-cells, 10
gemmation, 66, 69
Gemmulatrochus, 73
Gephyra, 61
Gersemia, 25
Gersemiopsis, 25
Gesner, 2
gland-cells, 10

INDEX TO THE ANTHOZOA

Godefroyia, 34
Gonactinia, 48, 59
Gonactinidae, 59
gonads, 40
Goéndul, 34
Gindulidae, 33, 34
Goniastrea, 74
Goniocora, 74
Goniophyllinae, 75
Goniophyllum, 75
Goniopora, 76
Gorgonia, 28

— development of, 14
Gorgonidae, 18, 28

Haddon, 7

Haime, 4, 70
Haimea, 15
Haimeidae, 15
Halcampa, 48, 44, 59
Halcampinae, 59
Halipteris, 34
Halisceptrum, 34
Halomitra, 76
Haplophracta, 71
Hartea, 15

Heider, A. von, 62
Heliastreea, 74
Heliolites, 36
Heliolitidae, 36
Heliopora, 36
Helioporidae, 19, 36
Herpetolitha, 76
Hertwig, O., 4
Hertwig, R., 4
Heteropsammia, 76
Heteroxenia, 17, 23
Hexactinia, 10
Hexactiniae, 59
Hickson, 22
Hydnophora, 74
Hymenogorgia, 28

Ilicigorgia, 25
Ilyanthidae, 59
Ilyanthinae, 59
Iiyanthus, 59
Imperato, 3
Isastrea, 74
Tsidae, 18, 28
Tsidella, 28
Tsidinae, 28
Tsis, 28

Johnston, J., 2
Jungersen, 30

Keroeides, 25
Klunzinger, 26

Koch, G. von, 4, 26, 61
Kolliker, A. von, 5

INDEX TO THE ANTHOZOA 83

Kophobelemnon, 34 Microtypa, 58 Peyssonel, 3
Kophobelemnonidae, 34 microtype, 51 Phellia, 60
Kowalevsky, 4 Milne-Edwards, 4, 70 Phycogorgia, 28
Monauleae, 48 Phyllactinae, 61
Lacaze-Duthiers, H. de, 4, | Monaulidae, 59 Phyllactis, 61
Monoxenia, 15 Phymanthidae, 61
Lamarck, 4 Monticuliporidae, 37 Phymanthus, 61
Lamouroux, 4 Montipora, 76 physa, 44
Leiopathes, 53, 55, 58 Mopsea, 28 pinnae, 31
Leiopathidae, 58 Mopseinae, 28 Placocyathus, 73
Leioptilum, 34 Mopsella, 25 Placosmilia, 74
Lemnalia, 25 Moseley, 4, 36, 71 Placotrochus, 73
Leptopenus, 76 Moseleya, 70, 75 Plasmopora, 36
Leptophyllia, 76 Muriceidae, 28 Platycaulos, 28
Leptoptilum, 34 Murocorallia, 71 Platygorgia, 28
Leptoseris, 76 muscle-banners, 11, 39 Plesiofungidae, 75
Leucoella, 25 muscular layer, 9 Plesioporitidae, 71, 76
Liponemidae, 61 Mussa, 69, 74 Pleurocorallium, 25
Lituaria, 34 Mycedium, 76 Pleurocyathus, 72
Lituarinae, 34 Plexaura, 28
Lobel, 2 Nannodendron, 24 Plexaurella, 28
Lobophytum, 24 nematocysts, 9 Plexauridae, 28
Lophogorgia, 28 Neohelia, 73 Pliny, 2
Lophohelia, 69, 73 nephridia, 7 Plumarella, 28
Lophoseris, 75 Nepthya, 24 Pocillopora, 73
Lyellia, 36 Nepthyidae, 18, 24 Pocilloporidae, 73
Lygomorpha, 34 nervous layer, 9 Podoseris, 76
Policella, 34
M‘Murrich, 49, 50 Octactiniae, 10 Pollaplophracta, 71
macromesenteries, 48, 49 Oculina, 73 Polycyathus, 73
Macrotypa, 58 Oculinidae, 73 Polyopidae, 61
macrotype, 51 Ogilvie, Miss, 56, 62, 71, | Polyopis, 46, 61
Madracis, 73 74, 75 polyp, 4
Madrepora, 76 Omphyma, 72 Polysiphonia, 61
Madreporaria, 45 Oractidae, 59 Polystomidium, 61
Madreporidae, 76 Oractis, 49, 59 Porites, 76
Meandrina, 74 Ovid, 2 Poritidae, 76
Mceandroseris, 76 Pratz, 56
| Malacactiniae, 55, 59 Pali, 62 Primnoa, 28
| Mammilifera, 58 Palythoa, 58 Primnoella, 28
Manicina, 43, 45, 63, 74 | Paractinia, 60 Primnoidae, 18, 28
Marsilli, 3 Paractininae, 60 Primnoinae, 28
Megalactis, 61 Paractis, 60 Primnoisis, 28
Melitodes, 25 Paragorgia, 25 Prionastrea, 70
: Melitodidae, 25 Paraleyonium, 24 Proactiniae, 58
Merulina, 74 Paramera, 57 Propora, 36
mesenterial filaments, 9, 37, | Paramuricea, 28 prorachis, 31
Paranepthya, 25 Protalcyonacea, 15
mesenteries, 8 Paranthus, 60 Protocaulidae, 34
— in Alcyonaria, 11 Parantipathes, 57 Protocaulon, 33, 34
— in Antipathidea, 54 Pararachides, 31 Protoptilidae, 34
— in Cerianthidea, 53 Parisis, 25 Protoptilum, 34
— in Zoantharia, 37-39, | Pavonaria, 34 Psammogorgia, 28
41 Peachia, 48, 59 Psammoseris, 76
— in Zoanthidea, 51 Peachiinae, 59 Pseudaxonia, 18, 19, 25
mesogloea, 6, 10 Pennatula, 34 Pteroeides, 34
metarachis, 31 Pennatulacea, 30 Pteroeididae, 34
Michelinia, 75 Pennatulidae, 18, 33, 34 | Pteropathes, 57
Micrabacia, 75 Pennatulinae, 34 Ptilosarcus, 34
micromesenteries, 48, 49 Perforata, 65, 76
Microptilum, 34 peristome, 38 Quelch, 56, 70, 71, 75

—

84 INDEX TO THE ANTHOZOA

Réaumur, 3
relationships of Zoantharia,
55, 56
Renilla, 13, 14, 34
Renillidae, 33, 34
respiratory system, 7
Rhizophyllum, 75
Rhizotrochus, 72
Rhodactinae, 61
Rhodactis, 43, 61
Rhodarea, 76
Rhodopsammia, 66, 76
Rondelet, 2
Rétteken’s muscle, 40
Rugosa, 56

Saccanthus, 57
Sagartia, 42, 60
Sagartinae, 59
Sarakka, 24
Sarcodictyon, 17, 20
Sarcophianthidae, 61
Sarcophianthus, 61
Sarcophyllum, 34
Sarcophyton, 24
Sars, 4

Savaglia, 61
Savigny, 4

scapus, 30, 44
Schizocyathus, 72
Schizopathes, 57
Schizopathinae, 57
Scleractiniae, 55, 61
Sclerisis, 28
Sclerobelemnon, 34
Sclerogorgia, 25
Sclerogorgidae, 18, 25
Scleronepthya, 25
Scleroptilum, 34
Scytalium, 34
Scytophorus, 48, 59
Semper, 76
Semperina, 25
sense-cells, 9

septa, 8, 62
Septocorallia, 72
Seriatopora, 73
Shaw, 3

Sicyonidae, 61
Sicyonis, 47, 61
Siderastrea, 75
Siebold, C. von, 4
siphonoglyphe, 7
Siphonogorgia, 25
Siphonogorginae, 25
siphonozooids, 11, 30
skeleton, 13, 37

Sinilotrochus, 73
solenia, 14, 16
Solenocaulon, 25
Sphenopidae, 58
Sphenopus, 58
Spongioderma, 25
Spongioderminae, 25
Spongodes, 24
Spongodinae, 24
Stachyodes, 28
Stachyptilidae, 34
Stachyptilum, 34
Stauria, 56, 75
Staurinae, 75
Stelechotokea, 19, 28
Stenella, 28
Stenogorgia, 28
Stenopora, 22
Stephanactis, 61
Stephanaria, 76
Stephanophyllia, 71, 76
Stephanotrochus, 73
Stichopathes, 57
Stolonifera, 19
stomodaeum, 7, 38
Streptelasma, 56, 72
Stutchbury, 76
Stylatula, 34
Stylobelemnon, 34
Stylophora, 73
Suberia, 25
Suberogorgia, 25
suleulus, 7, 37
suleus, 7, 11, 37
Swiftia, 28
Sympodium, 17, 20
Synalcyonacea, 15
synapticula, 63
Synarea, 76
Syringolites, 22
Syringopora, 21
Syringoporidae, 21

Tabernaemontanus, 3
tabulae, 63
Taractea, 61
Taxipathes, 57
Tealia, 46, 61
Tealiidae, 61
Telestidae, 29
Telesto, 18, 30
tentacles, 5, 37
Tetracoralla, 56
Thalassianthidae, 61
Thalassianthinae, 61
Thalassianthus, 61
Thamnastrea, 75

Thecidae, 36
Theophrastus, 2
Thouarella, 28
Titanideum, 25
Tournefort, 3
Trembley, 3
Triactis, 61
Trichoptilum, 34
Trochocyathus, 73
Trochoseris, 76
Trochosmilia; 74
trophozooid, 66, 75
Tubipora, 21
Tubiporidae, 21
Turbinaria, 76
Turbinolia, 73
Turbinolidae, 71, 72
Turbinolinae, 73
Tylopathes, 57

Umbellula, 34
Umbellulidae, 33, 34
unequal division, 69

Vaughan-Thompson, 4
ventrum, 7
Veretillidae, 33, 34
Veretillum, 34
Villogorgia, 28
Virgularia, 34 —
Virgularidae, 33, 34
Virgularinae, 34
Voeringia, 25

Wilson, E. B., 4
Wilson, H. V., 63,
Wotton, 2
Wrightella, 25

Xenia, 17, 23
Neniidae, 17, 23
NXiphigorgia, 28

Zaphrentidae, 71, 72
Zaphrentis, 72
Zaphrentoidea, 71
Zoantharia, 37
Zoanthidae, 58
Zoanthidea, 49, 58
Zoanthus, 58
zoochlorellae, 10
zooid, 5

zoophytes, 2
zooxanthellae, 10

CHAPTER VII.

THE CTENOPHORA.!

CLASS CTENOPHORA.
Sus-Cuass 1. TENTACULATA.

Order 1. Cydippidea.
» 2. Lobata.
», 9 Cestoidea.
» 4. Platyctenea.

Sus-Ciass 2. Nupa.
Order 5. Beroidea.

UNDER the name Ctenophora is comprised a small assemblage of
organisms, pelagic in habit, characterised by a well-marked biradial
symmetry, the possession of rows of swimming plates formed of
modified cilia, and a transparent gelatinoid body. The majority
of authors classify the Ctenophora as an aberrant group of the
Coelentera, the architecture of the body being compared with
that of a Hydromedusa ; on the other hand, several authors have
claimed affinities between the Ctenophora and Turbellarian worms.
It will be most convenient to describe the structure and develop-
ment of a typical form of the group, and to discuss its phylogeny
afterwards.

Though the Ctenophora are universally distributed and are
especially abundant in warm seas, they were not recognised until
1671, and then they were observed, not in warm or temperate
seas, but in the neighbourhood of Spitzbergen by a ship’s surgeon
named Friedrich Martens. Nearly a century later, in 1756, they
were again discovered at Jamaica by Patrick Brown, and two
species were included in the tenth edition of the Systema Naturae
under the names Volvox beroé and Volvox bicaudatus. Since the
beginning of the present century Ctenophora have been found
and studied in all quarters of the globe. They attracted the

1 By G. C.. Bourne, M.A.

2 THE CTENOPHORA

attention of the earlier zoological circumnavigators, Peron, Lesueur,
Quoy, Gaimard, and Chamisso ; and in 1829 Eschscholtz assigned
to them the systematic position near the Medusae, which they
have retained ever since. After Eschscholtz the Ctenophora were
studied by many observers, particularly by Leuckhart, Kélliker,
Gegenbauer, Fol, L. Agassiz, and Allman, and lately they have been
more closely studied by Kowalevsky, A. Agassiz, Metschnikoff,
and especially by Chun, whose monograph, forming the first
volume of the Fauna and Flora of the Gulf of Naples, is the
standard treatise on the subject.

The fundamental structure of the Ctenophora may con-
veniently be studied in two species, which may be procured in
abundance off the English coasts in the spring, summer, and
autumn months, Plewrobrachia pileus, Fabr. (=P. rhododactyla,
Agassiz), and Hormiphora plumosa, Agassiz.

The body is ovoid, and in Hormiphora it tapers somewhat
towards one end, on which is placed a wide aperture compressed
from side to side ; this is the mouth. At the opposite end of the
body is a shallow depression containing a sense organ of char-
acteristic structure. The line connecting mouth and sense organ
is the chief axis of the body; the extremity, at which the mouth
is placed, is distinguished as the oral pole, the opposite extremity
as the aboral or sensory pole.

The surface of the body is beset with eight meridional rows
of modified ectoderm, bearing very long cilia, fused together and
so disposed as to form a series of swimming plates called combs
or ctenes. The meridional rows are termed ribs or costae,
and they divide the body into octants. In both Hormiphora
and Plewrobrachia they begin at some little distance from the
aboral pole, in Hormiphora they extend downwards over about
two-thirds of the body, in Plewrobrachia pileus they reach down-
wards nearly to the mouth. On either side of the body, in
an interspace between two costae, is a pouch leading into a
considerable cavity hollowed out in the gelatinous body. From
each pouch projects a tentacle, a long solid filament furnished with
numerous accessory filaments.

The mass of the body is composed of a gelatinous substance,
so transparent that the main features of the internal anatomy
may be studied without dissection. The mouth leads into a
tolerably spacious sac which, like the mouth itself, is compressed
from side to side. This sac, usually called the stomach, is developed
as a secondary invagination of the epiblast, and is therefore a
stomodaeum. It extends upwards for some two-thirds of the way
towards the aboral pole, and there opens by a small orifice into a
second sac, the infundibulum, which is also compressed from side to
side, but in a plane at right angles to the first. Following Claus’s

i a ae

THE CTENOPHORA 3

terminology (9), the plane in which the stomodaeum is compressed
will be called the sagittal, that in which the infundibulum is com-
pressed the transverse plane. As the tentacles lie at either end of
the transverse plane, the latter is sometimes called the tentacular
plane.

As the whole plan of the Ctenophoran body is dominated by
these two planes lying at right angles to one another, it will be
convenient to refer the position of other organs tothem. Accord-

Fic. I.— All the figures are of Plewrobrachia pileus.

1.—The animal has been cut in half vertically rather to one side of the transverse plane
st, stomodaeum ; i, infundibulum ; ic, infundibular canal ; sfc, stomodzeal canals ; tre, transverse
a on which are seen the cut ends of the secondary canals; th, tentacle base; tsh, tentacle
sheath.

2.—The animal has been similarly cut in half in the sagittal plane. a, sub-sensory am-
pullae ; mc, meridional canals ; ssc, sub-sagittal and, str, sub-transverse gastrovascular canals.

8.—View of the gastrovascular system in an animal cut across just above the level of the
infundibulum. Lettering as before.

4.—View of the aboral aspect of Plewrobrachia showing the central otolith mass, the polar
fields, Pf; the four ampullae and two excretory openings, the eight ciliated furrows, the
costae and the fringed tentacles ; css, sub-sagittal and, ctr, sub-transverse costae.

5.—Diagram illustrating the symmetry of a cydippiform Ctenophore. SS, sagittal axis; TT,
transverse axis ; ssa, sub-sagitital radii; tra, sub-transverse radii.

ingly, organs which are adjacent to the sagittal plane will be
called sub-sagittal, those which are adjacent to the transverse plane
will be called sub-transverse.

The infundibulum is lined by endoderm, and is the true

25

4 THE CTENOPHORA

enteron, though the process of digestion is, for the most part,
carried on in the stomodaeum, which is provided in its upper
portion with a pair of longitudinal thickenings, the stomodzal
folds, serving to increase its surface. The products of digestion
pass into the infundibulum, and are thence distributed to all parts
of the body by canals which, taken collectively, constitute the
gastrovascular system. The gastrovascular canals, like the infundi-
bulum, are lined with endoderm.

We may conveniently distinguish two sets of canals—vertical
and horizontal. The vertical canals consist of a pair running
mouthwards, and a single axial vessel passing towards the aboral
pole. The former are blind diverticula running down, one on each
flattened side of the stomodaeum, and ending in the neighbour-
hood of the mouth (Fig. I. 1, 2, ste). The aboral vessel runs
straight towards the sense organ, bifurcates at a short distance
below it, and each branch again divides to form a pair of small
sacs or ampullae which lie immediately below the ectoderm, and
underneath the aboral sense organ. Each of the ampullae lies
in one of the angles formed by the intersection of the sagittal and
transverse planes. Two of them are closed sacs, but two, lying
diagonally opposite to one another, open to the surface by small
pores in the neighbourhood of the polar fields. It is a rule, with-
out exception, in the Ctenophora that, if the animal is viewed from
the sagittal aspect, the ampulla farthest from the spectator on the
left, and the one nearest to him on the right, open by these so-called
excretory pores (Fig. I. 4, and Fig. II. 1, exp).

The horizontal gastrovascular canals serve to place the infundi-
bulum in connection with the bases of the tentacles, and with the
eight meridional canals which run immediately beneath the costae.
A single pair of wide vessels, lying in the transverse plane, starts
from the infundibulum at the level of its opening into the stomo-
daeum. Each transverse vessel, after a short course, bifurcates at
a wide angle, and its branches again divide, forming on either
side of the body four canals, two of which are sub-sagittal and two
sub-transverse (Fig. I. 3; 5). Each canal passes direct to a costa,
and beneath it is produced orally and aborally into a long diver-
ticulum which lies immediately below the costa and ends blindly,
forming the sub-costal meridional canal. The gonads are developed
on the walls of these sub-costal canals.

The space between the stomodaeum, gastrovascular system,
and body walls is occupied by a gelatinoid substance, in which are
imbedded numerous muscle fibres, whose structure and arrange-
ment will be described further on.

The sensory organ at the aboral pole consists of a shallow de-
pression of the ectoderm, lined by a modified and probably sensory
epithelium. Within many of the epithelial cells are formed cal-

—— Oe

THE CTENOPHORA 5

careous sphaeroids (otoliths); and, according to Samassa (21),
when the otoliths are fully formed, they are ejected, still sur-
rounded by the remnants of the cells in which they were formed,
and become aggregated together to form a mulberry-like mass.
The otolith mass is supported by four ‘ balancers,” delicate lamellae
of peculiar shape formed by fused cilia. The whole structure,
sensory pit and otolith mass, is covered over and _ protected
by a transparent dome formed by fused cilia (see Fig. II. 1, 2).
The four balancers lie in the angles of intersection of the sagittal and

Fie. IL.

1.—Surface view of the sense organ of Hormiphora plumosa. Pf, polar fields; a, ampullae ;
xp, excretory pores ; 7, groups of gland cells; cf, ciliated furrows. (After Chun.)
2.—The same seen from the side. ot, otolith mass; cu, cupule formed of fused cilia.

transverse planes; from the base of each of them two rows of ciliated
furrows run outwards to end in the uppermost comb of each costa.
The sensory pit is produced on either side, in the sagittal plane,
into an elongated band-like ciliated tract. These tracts are
known as the polar fields (Fig. I. 4, and Fig. II. 1, Pf), and it
was supposed that they served as olfactory organs, but Samassa
(21) states that they are nothing more than tracts of simple
ciliated epithelium, devoid of sensory cells, so their function re-
mains unknown. Samassa denies the existence of any nervous
structures beyond those already mentioned; but Hertwig (13),
whose observations have recently been confirmed by Bethe (5),
describes a sub-epithelial nerve plexus similar to that which occurs
in Medusae.

6 THE CTENOPHORA

In the majority of the Ctenophora locomotion is effected solely
through the action of the combs of the costae. Only in the much
modified family of the Cestidae is the ciliary action supplemented
by sinuous movements of the elongated, band-like body.

A costa is made up of a number of short transverse rows of

modified ectoderm cells, bearing exceedingly long cilia. The cilia
are fused together to form the swimming plate or comb. The
basis of each comb is a cushion composed of large columnar cells ;
these cells have broad bases and narrower ends, so that they con-
verge together (Fig. III. 5). According to Samassa, the ciliated
cells of one comb are in direct organic continuity with those of the
next succeeding comb by means of branched processes of the bases
of the cells, which processes traverse the intervening space, and admit
of stimuli being conducted from comb to comb (Fig. III. 4). The
cilia are borne on the narrower ends of the columnar cells, and are
fused to form a plate which is bent downwards at a tolerably sharp
angle at a short distance from the surface. When in action the
comb is straightened out so as to give a sharp stroke in an upward
—that is, in the aboral—direction, and then it swings slowly back
to the bent position of rest. The combs of each costa contract in
succession from the aboral towards the oral pole, their successive
action giving rise to the appearance of a wave travelling in the
same direction. It follows that the action of the combs drives the
animal through the water mouth forwards, its progress being just
the opposite to that of a Medusa. The activity of the combs of
each costa is directed and controlled by the aboral sense organ.
The structure of the latter shows it to be an organ of balance. If
the Ctenophore be tilted over to one side the otolith mass bears
down upon the balancer of that side, and the impulse thus originated
is transmitted from cell to cell of the ciliated furrows till it reaches
the first combs of the costae to which the furrows are distributed.
These combs immediately contract, and the stimulus is conveyed
from comb to comb by means of the processes of the ectoderm cells
described above. Thus the ciliated furrows function as nerves,
though they do not contain nerve fibres or nerve ganglion cells,
and the transmission of stimuli is effected by simple cell contact.
It must be borne in mind, however, that there is also a sub-
epithelial nerve plexus with ganglion cells and nerve fibrils, though
the latter are not known to be connected with the aboral sense
organ.

The tentacles of the Ctenophora serve for the capture of prey,
and are not used in locomotion. They are most fully developed
in the Cydippidae (//ormiphora and Pleurobrachia); are present,
though much modified, in the Cestidae and Lobatae, but are absent |
in the Beroidae. In Pleurobrachia and Hormiphora the tentacle,
consisting of a tentacular base and the tentacle proper, is retractile

————

THE CTENOPHORA 7

within the tentacle sheath, a wide sac-like invagination of the
ectoderm. The tentacular base is the broad proximal extremity of
the tentacle, and is inserted on the inner or axial side of the
tentacular sheath. It is penetrated by a pair of saccular cavities
which are prolongations of the transverse gastrovascular canals.

Fie. IIT.

1.—Two lasso-cells (after Samassa). gl, glandular portion of lasso-cell ; ef, central filament ;
sf, spiral filament; , nucleus of central filament.

2.—Section through the epithelium of the base of a tentacle of Hormiphora, showing the
development of the lasso-cells from, ge, gland cells and, ef, filaments formed from, in, the
interstitial tissue.

8.—Two otoliths of Beroé (after Samassa). m, nucleus.

4.—Section through the ectoderm cushion at the base of acomb. Be, basal cells of the comb ;
p, their processes ; ep, connecting process going to the next comb. (After Samassa.)

5.—Diagrammatic section through a comb. Be, basal cells; cil, plate formed of fused cilia.
(After Chun.)

6.—Attachment of the radial muscles, rm, to the stomodal sphincter muscles, rim, in Beroé.
(After Samassa.)

7.—Epithelium of Cestus veneris, showing gland cells, gle; in various stages of development
imbedded in a coenocytial interstitial tissue, it.

8.—Diagram showing the position of the ovaries, ov, and the spermaries, t, in the hypoctenial
diverticula of the meridional canals in Eucharis multicornis, and in Bolina alata.

9.—Diagram showing the position of the ovaries and spermaries in Detopea kaloktenota and
Bolina hydatina.

10.—Diagrain of the tentacle base of Hormiphora plumosa, after Chun. i, infundibulum ;
st, stomodaeum ; stc, stomodeal canal; fe, tentacular canal; af, accessory filament; m,
muscles ; tsh, tentacle sheath.

The partition between the tentacular canals is called the tentacle
stem; it contains muscles which converge from the wall of the
tentacle sheath to the tentacle itself, where they form a solid axial

8 THE CTENOPHORA

cord, from which muscular slips are given off to the accessory
filaments. The tentacle itself is a solid, muscular, and exceed-
ingly extensile filament (Fig. II. 10). The accessory filaments
are simple and thread-like in Pleurobrachia, but in Hormiphora
certain of them are thickened and furnished with digitiform
appendages which, from their supposed resemblance to a minute
Eolis, are often called eolidiform appendages. The whole surface
of the tentacle and its accessory filaments is covered by densely
crowded “ lasso-cells,” structures characteristic of the Ctenophora,
which will be described in detail further on.

The musculature of the Ctenophora is wholly derived from
the mesoblast, and there are no epithelio-muscular cells. The
muscle fibres are for the most part much branched, and are not
grouped into bundles except at the bases of the tentacles, in the
tentacles themselves, and im the regions of the mouth and aboral
sensory organ, where they form sphincters. There is a well-marked
layer of musculature under the body wall, consisting of an external
layer of longitudinal, and an internal layer of transverse fibres. A
similar musculature invests the stomodaeum and the gastrovascular
canals. The gelatinous substance of the body is traversed by
numerous fibres, whose general direction is radial, from the stomo-
daeum and gastrovascular system to the body wall.

The histology of the Ctenophora has been carefully studied by
Samassa (21), to whose paper the reader is referred for details.
The epithelium of the body is peculiar, being formed of large gland
cells lying in an interstitial tissue, in which many nuclei, but no
cell boundaries, are to be distinguished. In the neighbourhood of
the aboral sense organ, the ciliated ridges and the costae, the gland
cells become smaller and less numerous, and the interstitial tissue
is replaced by a simple cubical epithelium. The most characteristic
histological feature of the Ctenophora is the presence of the
lasso-cells (Fig. III. 1, 2). Each lasso-cell has the shape of a~
hemispherical cup, the convexity turned outwards and covered
with minute sticky papillae. To the inner concave side are
attached two filaments: the one an exceedingly fine central proto-
plasmic thread, in the upper part of which a much attenuated
nucleus can generally be distinguished. The other is a contractile
fibre thicker than the first, attached like it to the centre of the
convex surface of the cup, and coiled in the first part of its course
in a close spiral. Eventually the spiral thread tapers off into a
fine filament, which, according to Chun, is attached to the muscle
fibres forming the axis of the tentacle. The lasso-cells lie close
together, forming a complete investment for the tentacle, with only
very sparse interstitial tissue between. When any foreign body
comes into contact with the tentacle, the lasso-cells adhere to it
by their sticky convex surfaces, are withdrawn from the surface,

THE CTENOPHORA 9

and the object is held fast by the spiral thread which remains
attached to the tentacle.

According to Samassa, the lasso-cells are formed from two cell
elements. The hemispherical cup is the product of a meta-
morphosed gland cell, the nucleus of which may often be dis-
tinguished in the convexity of the cup near the point of attachment
of the spiral thread. The straight, thread-like filament and the
spiral, contractile filament are formed from an elongate cell, which
is apparently a metamorphosed interstitial cell. If Samassa’s
account is correct, it is obvious that there is no homology between
the lasso-cell, composed as it is of two metamorphosed cells, and
the nematocyst which is the entoplastic product of a single cell.

All the Ctenophora are monoecious, the ova and spermatozoa
being formed from the endodermic epithelium lining the sub-costal
meridional canals. The ova are developed on one side, the
spermatozoa on the other side of each canal. In the sub-sagittal
canals the ova are borne on the sides nearest to the sagittal plane, in
the sub-transverse canals they are borne on the sides nearest to the
transverse plane. In Pleurobrachia and Hormiphora, as in the
Cydippidae generally, the ovaries and spermaries are simply
paired outgrowths from the walls of the meridional canals, and
extend as two long bands throughout the entire length of each.
As a rule, all the eight meridional canals bear gonads in the
Ctenophora, but in Euchlora rubra and Charistephane fugiens the
gonads are formed only in the four sub-transverse canals. In the
Lobatae and Beroidae the gonads, whilst occupying the typical
position, are somewhat modified in detail. In the former group
the meridional canals are produced laterally to form diverticula
underlying each comb. In Lucharis multicornis and Bolina alata
the ova and spermatozoa are found in these diverticula only, but
in Deiopea and Bolina hydatina the diverticula are sterile, the
reproductive cells being confined to the sections of the meridional
canals which lie between successive combs (Fig. III. 8 and 9).
In the Beroidae the meridional ‘canals are produced laterally into
short, branched diverticula in which the sexual cells are developed
(Fig. X.).

The ova in most cases are deposited singly and are fertilised
in the sea-water. The breeding season in Northern seas lasts
through the summer months, in the Mediterranean throughout the
year. The ovum is centrolecithal, consisting of an inner vacuolated
mass surrounded by a layer of granular protoplasm. It is enveloped
by a vitelline membrane rather widely separated from the surface of
the egg, the space between being filled with a gelatinous substance.

The most interesting feature in the development of the Cteno-
phora is the formation of a definite mesoblast. We owe this
important discovery to Metschnikoff (18), whase observations

Io THE CTENOPHORA

have been confirmed in all essential particulars by the unpublished
researches of Mr. T. H. Riches. The segmentation is holoblastic.
By three successive meridional cleavages the ovum is divided into
eight blastomeres, in each of which the granular protoplasm is
aggregated at one pole, the vacuolar deutoplasm at the other
pole (Fig. IV. 2). By an equatorial division a portion of the
granular protoplasm is next segmented off from the upper pole
of each blastomere, the embryo now consisting of eight upper
protoplasmic micromeres and eight large inferior macromeres (3).
The succeeding divisions lead to increase of the number of micro-
meres which are formed partly by continued budding off of small
cells from the four macromeres, partly by division of the eight
micromeres first formed. When some thirty to fifty micromeres
are present the macromeres cease to bud off fresh micromeres and
themselves divide. Reference to Fig. IV. 4 shows that the eight
macromeres are not all of equal size. There are four larger macro-
meres, median and inferior, and four smaller macromeres, lateral
and superior. The median macromeres divide first, the lateral
somewhat later, and this sequence is followed through the suc-
ceeding steps of development. In the next stage (6) the embryo
is ring-shaped, consisting of a circlet of sixteen macromeres
surrounding a central cavity widely open both above and below.
On one aspect, which we may at once call the aboral aspect, the
macromeres are covered over by the continually increasing cap
of micromeres. The micromeres at this stage show a four-rayed
symmetry, and on the aboral aspect they surround a cross-shaped
opening, the pseudoblastopore, erroneously described by Chun (6)
as the blastopore. The micromeres spread more and more over
the surface of the macromeres and extend towards the lower
surface. The next stage leads to the formation of the mesoblast.
The nuclei of the sixteen macromeres, which at first were situated
near the aboral pole, travel towards the opposite pole (7). The
micromeres meanwhile have increased in number, the size of the
pseudoblastopore is decreased, and there is at the lower pole a
roughly quadrilateral area bounded by micromeres which is the
true blastopore. Next follows a fresh division of the macromeres ;
first the eight median, later the eight lateral macromeres bud off
each a small cell at the blastoporic pole, thus there is formed a
median group of sixteen cells, which are the mesoblast. The
three germ layers are now established. The micromeres form
the epiblast, the macromeres the hypoblast, and the sixteen cells

above mentioned are the mesoblast. Thus far the embryo has —

been formed by epibolic growth of the epiblast over the hypo-
blast. This is now succeeded by a process of embole. The
macromeres are rotated in such a manner that their previously
lower ends face inwards, their previously upper ends face out-

THE CTENOPHORA II

wards. As a result of this change of position a central cavity,
the enteron, is formed, and the mesoblast cells are carried

Fic, IV.—Development of Callianira bialata (after Metschnikoff).

1.—Ovum surrounded by the vitelline membrane.

2.—Stage with eight blastomeres.

3.—Side view of a stage with sixteen blastomeres, eight larger macromeres, mac, and eight
smaller micromeres, mic.

4.—A similar stage viewed from above.

5.—Side view of a later stage ; the micromeres have increased in number, and the macro-
meres are beginning to divide.

6.—Aboral surface of an olderembryo. The micromeres form a four-rayed plate, covering
the upper surfaces of the macromeres and surrounding a cross-shaped cavity, the pseudo-
blastopore, pbl.

7.—Vertical section of the same embryo as the preceding, showing the large macromeres
covered by the micromeres, except in the regions of blastopore, b/, and pseudoblastopore, ps).
The nuclei of the macromeres are now at the blastoporic pole.

8.—Oral surface of an older embryo. bl, blastopore ; mes, mesoblast plate; ec, ectoderm ;
en, endoderm.

9.—Vertical section of an older embyro showing invagination. mes, mesoblast ; the pseudo-
blastopore is closed.

10.—An embryo somewhat older than 9.

11.—A later stage showing the stomodaeum, st, the enteron, ent, and the mesoblast, mes,
which is spreading out as a plate on either side beneath ectodermic thickenings, which are the
primordia of the tentacles.

12,—Aboral view of a somewhat later stage, showing the cross-shaped mesoblast plate.
ww, wandering cells of the mesoblast.

13.—Vertical section in the transverse plane of an embryo in the same stage as 12. so, sense
organ ; mes, mesoblast ; tr, primordium of the tentacle ; ent, enteron ; st, stomodaeum.

14.—A later stage. tt, tentacles; mt, contractile muscles of the tentacles formed from the
mesoblast ; ms, mesenchymatous cells derived from the wandering cells of the mesoblast
shown in 12.

upwards from the blastoporic towards the pseudoblastoporic pole
(9). According to Riches, the pseudoblastopore is closed before

12 THE CTENOPHORA:
ea es eee

invagination by concrescence of the epiblast at the upper pole,
and the embryo is now a gastrula (10). A secondary invagination
of the ectoderm gives rise to a stomodaeum, and the mesoblast
cells travel to the aboral pole and spread out beneath the ectoderm
to form a plate of cells from which all the muscles of the body are
eventually developed. The tentacles are first seen as thickenings
of the ectoderm in the transverse plane, to which two plates of
mesoblast attach themselves. The mesoblast plates extend not
only in the transverse, but also in the sagittal plane, so that a
cross-shaped figure is formed, the exact significance of which is
not known (12). It is supposed by some that it is an indication
of the existence of sagittal tentacles in the ancestral Ctenophore.
The sense body is formed from an epiblastic thickening at the
aboral pole. The further stages of development can be understood
by reference to Fig. IV. 13, 14, and the reader is referred to
Metschnikoff’s and Chun’s works for details.

All the Ctenophora reproduce themselves sexually. There is
no alternation of generations. In the Cydippidae and Beroidae
development is direct, but in the Lobatae and Cestidae there is a
metamorphosis. The larvae of these forms are cydippiform and
only gradually acquire their adult characters. In connection with
this metamorphosis a peculiar sequence of juvenile fertility,
adolescent sterility, and adult fertility has been observed in the
Lobatae, and has been named by Chun, its discoverer, Dissogony.
In the warm months the cydippiform larvae of Eucharis multicornis
and Bolina hydatina, as soon as they have escaped from the egg
membranes, and whilst they are only some *5 — ‘2 mm. in diameter,
become sexually mature and develop ova and spermatozoa in the
four sub-sagittal meridional canals. The ova are fertilised and give
rise to fresh cydippiform larvae. In the parent larva, after a brief
period of sexual activity, the gonads degenerate and a barren period
succeeds, during which the larva goes through a complicated meta-
morphosis. At the end of the metamorphosis the animal, now
much larger and indued with the full characters of a lobate Cteno-
phore, becomes a second time sexually mature, gonads being
developed in all the eight meridional canals (see Chun, 8).

With few exceptions zoologists, since the time of Eschscholtz,
have been agreed in ranking the Ctenophora as a class of the
Coelentera, although much evidence has been brought forward
of late years to show that they have decided affinities with
Platyhelminthes, particularly with the Polyclada (see Lang, 17).
The polyclad affinities of Ctenophora are regarded as tending to
prove that the Polyclada are descended by way of the Cteno-
phora, or, at least, by way of a Ctenophore-like ancestor, from the
Coelentera. Such an argument implies that the Ctenophora are
indubitably Coelentera.

THE CTENOPHORA 13

The characters of the Ctenophora which are relied on as
evidence of their Coelenterate nature are as follows:—1. The
existence of a gastrovascular system, and the absence of a separate
body cavity or coelom. 2. The general shape and architecture of
the body, its radial symmetry, and the existence of an abundant
gelatinous material between the two primary layers—the ecto-
derm and endoderm. 3. The presence of tentacles, which are
likened to those of a Medusa. 4. The position of the gonads, and
the derivation of the sexual cells from the endoderm. 5. The exist-
ence of a sub-epithelial nerve plexus resembling that of Medusae.
6. The supposed homology between lasso-cells and nematocysts.
7. The absence of nephridia. In a more special manner it has
been sought to compare the Ctenophore directly with a Medusa
or with an Anthozoan zooid. Thus the general surface of the
Ctenophoran body has been homologised with the exumbrellar
surface of a Medusa ; the stomodaeum with the sub-umbrellar cavity ;
the gelatinous mesoderm of the one with the mesogloea of the other;
the gastrovascular canals with the radial canals ; the Ctenophoran
tentacles with the marginal tentacles of the Medusa. These homo-
logies appeared at one time to be established beyond all cavil by
the discovery of Ctenaria ctenophora, a Cladonemid Anthomedusa,
described by Haeckel (12) as a form directly intermediate between
the Hydromedusae and the Ctenophora.? Ctenaria (see Fig. V.)
is an ovoid Anthomedusa, with a relatively small sub-umbrellar
cavity, the aperture of which is still further diminished by the velum.
The mouth opens at the end of a manubrium, and is surrounded by
a circlet of sixteen oral tentacles. The gastral cavity is divided
by a constriction into an upper and a lower moiety, the former
of which is homologised with the infundibulum of Ctenophora.
From the lower moiety four perradial gastrovascular canals are
given off, each of which bifurcates to form two adradial canals. The
eight adradial canals thus formed are connected round the margin
of the umbrella by arinmgcanal. There are two perradial marginal
filamentous tentacles beset with accessory filaments. At the base
of each tentacle is a pocket-like cavity in the exumbrella, lined by
batteries of nematocysts ; it is doubtful whether the tentacles are
retractile within these pouches. On the surface of the exumbrella
are eight adradial meridional ridges, made up of nematocyst
batteries. There is no apical sense organ, and the gonads are
borne, as in all Anthomedusae, on the manubrium. The
resemblange of Ctenaria to the Ctenophora is quite superficial.
One has only to compare the eight nematocyst stripes of the one
with the highly specialised ciliated costae of the other to see their

1 “‘Fine neue héchst interessante pacifische Form, Ctenaria ctenophora, welche
ich als eine unmittelbare Uebergangsform von Gemmaria-iihnlichen Anthomedusen
zu Cydippe-ihnlichen Ctenophoren auffassen muss.”

14 THE CTENOPHORA

essential difference, and, for the rest of it, nematocysts do not
occur in the Ctenophora.'| The sub-umbrella cannot be compared
either in its development or in its adult relations to a stomodaeum.
There is a superficial resemblance between the gastro-vascular
system of the two forms, but even if we pass over the absence
of anything representing the manubrium and oral tentacles in
Ctenophora, we find an essential difference in that the endoderm
lamella, in which the radial canals of the Anthomedusan are

Fia. V.

Ctenaria ctenophora, Haeckel. A, side view; B, two horizontal views, that ‘to the left
representing the surface of the aboral hemisphere, that to the right a section passing nearly
equatorially. a, the right adradial ridges of nematocysts; b, mesoglea of the umbrella;
e, circular muscle of the umbrella; d, longitudinal muscles of the umbrella; e, the gastral
cavity ; /, the sixteen oral tentacles; g, the four perradial gonads borne on the manubrium 5
h, the four perradial gastrovascular canals ; i, the eight adradial bifureations of the preceding ;
k, ring canal at the umbrellar margin; J, velum: m, pocket-like cavities in the exumbrella
situated at the bases of the tentacles and lined with nematocysts ; n, the tentacles ; 0, the
upper moiety of the gastral cavity, called by Haeckel the infundibulum.

‘ . < . oe
hollowed out, is entirely unrepresented in the Ctenophora. Nor
is there any ring canal in the latter group. The tentacles of
Ctenaria are lined by endoderm, their musculature is epithelial ;
the tentacles of Ctenophora have a solid axial cord of muscular
fibres derived from mesoblast. The sub-tentacular pouches of
Clenaria correspond neither in position nor in their relations to
the tentacles to the tentacular sheaths of Ctenophores, and the
existence of such nematocyst pouches, as well as the existence of
only a single pair of perradial tentacles, is paralleled in other

1 With one exception.

THE CTENOPHORA 15

Medusae which are not endowed with superficial Ctenophore-like
characters. The so-called infundibulum of Ctenaria proves to be a
brood pouch similar to that in the allied Eleutheria, and the Medusa
is devoid of any trace of the aboral sense organ so characteristic
of the Ctenophore. ‘The position of the gonads is also different
in the two forms. The gelatinous tissue and the musculature of
the Ctenophora are mesoblastic, in the Anthomedusan they are
ectodermal in origin. Add to this the fact that the locomotion of
the Ctenophora is essentially ciliary, that of the Medusae muscular,
that the symmetry of the one group is radial, whilst in the other
it is biradial, and it must be conceded that the Medusoid affinities
of the Ctenophora are untenable.

A comparison of the Ctenophora with the Anthozoa offers more
satisfactory grounds of homology. The ciliated ectoderm of the
Anthozoa might possibly be the antecedent of the specialised
ciliated bands which form the costae of the Ctenophora. The
stomodaeum of the Ctenophora and Anthozoa may fairly be
homologised. In both cases it is compressed in a plane which is
known as the sagittal plane, and in both cases the gastrovascular
system exhibits-a biradial symmetry with regard to that plane.
Further evidence is afforded by the comparison of developmental
stages. In both the Anthozoa and the Ctenophora there is a stage in
which the gut is produced into four saccular pouches, so that the
embryo has a four-rayed symmetry. This condition, which is
typical in the Ctenophora, is best seen in the young Arachnactis
amongst the Anthozoa, but may also be distinguished in the larvae
of Actinidae. It would be idle to deny the significance of these
features, but it must be recollected that the Ctenophora have many
features peculiar to themselves. ‘The costae and their combs, though
doubtless a specialisation of a primitively uniformly ciliated surface,
are characteristic of Ctenophora; so is the aboral sense organ,
to which there is no parallel in Anthozoa. The solid muscular
tentacles of the Ctenophores cannot be homologised with the
hollow tentacles of the Anthozoan. There is no epithelio-muscular
system in Ctenophora, and the musculature differs both in origin
and in structure from that of Anthozoa, and indeed all other
Coelentera. The nematocysts so characteristic of Coelentera are
replaced in Ctenophora by the lasso-cells, structures of an entirely
different nature.

Finally, there are those who would question whether any
animals possessing a mesoblast can properly be called Coelentera.
The Coelentera, as originally defined by Leuckart, are animals
in which there is no body cavity or coelom separate from the
digestive cavity or enteron; the two being represented by a
single cavity, the gastrovascular cavity or coelenteron. According
to this definition the Ctenophora are certainly Coelentera. In

16 THE CTENOPHORA

typical Coelentera one or other of the two primary layers,
ectoderm or endoderm, retains the functions which in Coelomata
are handed over to mesoblast. Hence we find epithelio-muscular
cells derived chiefly from ectoderm in Hydrozoa, chiefly from
endoderm in Anthozoa. The researches of Metschnikoft, confirmed
by Samassa, have shown that a mesoblast is formed in the
Ctenophora, that there is no epithelio-muscular system, but that
the musculature is wholly derived from the mesoblast. At the
same time it must be duly borne in mind that “ mesoblast” is
nothing more than an embryological segregation of those cells
derived in Coelentera or Diploblastic animals from one or both of
the primary germ layers which are in Coelomata destined to give
rise to the coelom and the tissues of its walls. Greater weight,
must be attached to the presence of the gastrovascular systém in
Ctenophora than to the embryonic exhibition of “a mesoblast.”

CSS.
Fia. VI.

Ctenoplana Kowalevskii, Korotneff (after Willey). tt, tentacles; tsh, tentacle sheaths ;
ctr, sub-transverse costae ; css, sub-sagittal costae; st, ‘‘stomach” (? stomodaeum), 1, 2, 3, 4,
the four principal lobes of the infundibulum; pf, sensory tentacles representing the polar
fields ; pg, pigment spots.

The affinities of the Ctenophora with the Polyclada remain
to be considered. These affinities, first suggested by Selenka on
embryological grounds, were rendered more probable by the
discovery of Coeloplana Metschnikoffii, a form supposed to be
intermediate between Planarians and Ctenophora, and were urged
with considerable force by Lang (17). The discovery of Cteno-
plana Kowalevskii, an animal allied to Coeloplana, by Korotneff (14)
served to confirm this view.

Ctenoplana has recently been rediscovered by Willey (22),
who has given a more exact account of its habits and anatomy
than Korotneff was able to do. It is a Ctenophore, flattened so
much that the principal axis joining mouth and sense organ is
extremely short. Hence one can distinguish a dorsal or aboral

a

THE CTENOPHORA 17

and a ventral or oral surface. It has eight very short ribs with
the characteristic combs, which can be withdrawn into’ or evagin-
ated from pouch-like cavities in the body wall. There is a single
pair of pinnate tentacles retractile within tentacle sheaths; the
tentacles are solid and muscular. In the centre of the aboral
surface of the body is a sense organ, consisting of an otolith mass
suspended by stiff cilia, and two crescentic rows of ciliated ten-
tacles or papillae, which are evidently homologous with the polar -
fields, and recall the lappet-like processes of the edge of the polar

‘fields of the Beroidae (Fig. X. pf). The mouth is circular and

leads into a “stomach,” which is compressed in the sagittal plane ;
it is not known whether the “stomach” is a stomodaeum. An
infundibular vessel passes from the aboral end of the stomach
towards the sense organ, which it embraces without opening to
the exterior. From each of the two flattened sides of the
stomach a narrow canal, lying in the transverse plane, leads into
a pair of saccular lobes, and from these numerous diverticula are
given off forming a peripheral canal system. These peripheral
canals may be compared with the canals of the lobes of Lobatae.
The testes are situated at the bases of the two saccular lobes at
either end of the main transverse canal of the gastrovascular
system, and they have ducts which open to the exterior just below
the costae. The ovaries have not been observed. Ctenoplana
either swims by means of its combs, or crawls on the bottom by
its ventral surface. It can also attach itself, like a Planarian,
ventral surface uppermost, to the surface film of the water. Its
body is thickened in the transverse plane, and the sagittal margins
are produced into two thin rounded lobes. In swimming the
lobes are folded together like the leaves of a book. It should be
noticed that the lobes of Ctenoplana correspond in position with
those of the Lobatae. The ventral surface of Ctenoplana is ciliated,
but, excepting for the costae and sensory tentacles, there are no
cilia on the dorsal surface.

Unfortunately we have only a meagre account of the anatomy
of Coeloplana. It appears, in general, to resemble Ctenoplana, but
has no costae, and the whole surface of the body is uniformly
ciliated. Both Ctenoplana and Coeloplana have been said to exhibit
remarkable Planarian affinities because of their dorso-ventrally
flattened bodies, their crawling habits, and the ciliation of the
ectoderm, partial in the case of Cfenoplana, complete in the case of
Ceoloplana. Not much weight can be attached to these characters.
Habit is a very insecure guide to affinity. One of the Cydippidae,
Lampetia pancerina, crawls on its oral surface, everting the stomo-
daeum so as to form a broad creeping surface. The flattened
bodies of Cfenoplana and Coeloplana are clearly correlated with the
adoption of the creeping habit already foreshadowed in Lampetia.

18 THE CTENOPHORA

A tendency towards dorso-ventral compression is not unknown in
typical Ctenophora, for in Deiopea (Fig. VIII.) the main axis is
considerably shortened and the sagittal axis lengthened by the
development of the lobes. Ctenoplana is an undoubted Ctenophore —
modified as a result of the assumption of creeping habits. It —
still retains the power of swimming, and has not lost the typical —
Ctenophoran costae. Coeloplana is still more modified and has lost —
the costae. The features in which Ctenoplana differs most from
Ctenophora are: the absence of nieridional sub-costal canals, and
as a consequence the development of gonads in a more proximal ~
part of the gastrovascular system; the presence of genital ducts
and the presence of a peripheral canal system, which, however, is

paralleled in the Beroidae and Lobatae. Whilst there can be no

Fic. VII.

Coeloplana Metschnikowii (slightly altered from Kowalevsky). 0, mouth; d, cavity of the
digestive canal; i, islets of tissue; c, circular canal; d’, one of the four diverticula of the
digestive canal ; ss, cecal offsets of the digestive canal, terminating in crescentic enlargements
about the otolith sac; ot, vesicle with a group of otoliths; ts, tentacle sheaths ; m, muscular
fibre of tentacles.

doubt that Ctenoplana is a Ctenophore, and not very distantly
related to the other members of the group, it is a question whether
it is a primitive or a much specialised form. Willey (22) is
decidedly of the opinion that it is primitive. He sees in it the
representative of the littoral ancestor from which both the pelagic
Ctenophora and the Platyhelminthes have been derived. In point
of fact we have no evidence as to whether Ctenoplana or Coeloplana
are primitive or derived forms ; such evidence can only be furnished
by their development and larval history, which are unknown. If
Ctenoplana should prove to have a cydippiform larva like the
Cestidae and Lobatae, then there can be no doubt that it is a
derived form; if it should prove to have a direct development
without a metamorphosis, then the probability will be that it is a
primitive form. In the present state of our knowledge it cannot
be said that the existence of Ctenoplana and Coeloplana gives any j

THE CTENOPHORA 19

satisfactory evidence of the relationship of Platyhelminthes to
Ctenophora, still less of the descent of the former group from the
latter. The most that can be said is that Ctenoplana and Coeloplana
afford an interesting suggestion as to how the Polyclada might
conceivably have been derived from a Ctenophore-like ancestor.
But whilst we decline to attach very much importance to the
resemblance between Ctenoplana and the Polyclada, we cannot
ignore other points of resemblance between the Ctenophora and
the Platyhelminthes. The earlier stages of segmentation, the
formation of the gastrula, the outgrowth of the primitive mesoderm
cells into four mesodermal bands placed crosswise, and the forma-
tion of the mesenchymatous mesoderm from these bands, are
features in which the young Polyclad resembles the young Cteno-
phore in a remarkable degree. The gelatinous mesoderm of
Ctenophora, with its layers of longitudinal, transverse, and
radiating branched muscle fibres, most nearly resembles the
mesenchyme of Turbellarian worms, and the ciliated larvae of
many Platyhelminthes, more particularly the Pélidiwm larva of
Nemertines and the larva of Stylochus pilidiwm, with its uniform
coat of cilia, its aboral sense organ, its stomodaeum or pharynx,
and its enteron lined with endoderm cells, are most suggestive of
the hypothetical ancestor from which both the Turbellaria and
the Ctenophora may have originated. The conclusion is that the
Turbellaria, the Nemertines, and the Ctenophora are descended
from a common ancestor which is most nearly represented by the
larva of Stylochus. Such an ancestor would be spherical or hemi-
spherical in shape, would have an aboral sense organ consisting of
a plate of thickened ectoderm provided with long stiff cilia. The
line joining mouth and sense organ would be the chief axis of the
body. The digestive tract would consist of a stomodaeum and a
more or less spacious sacculated enteron, and would be surrounded
by a mesenchymatous tissue consisting of a gelatinous matrix
traversed by branched muscular fibres, derived from a special germ
layer, the mesoblast. Such an ancestor would itself be a Coelen-
terate and have been derived from a Coelenterate ancestor, and
very probably from a form resembling the early larvae of Actinians.
The Ctenophora are classified as follows :—

CLAss CTENOPHORA.

Sus-Cuass 1. TENTACULATA. With tentacles.
OrvDER 1, Cydippidea, Lesson.

Ctenophora of spherical, cylindrical, or compressed form, with two
simple or branched tentacles retractile within tentacular sheaths, The
meridional and stomodzal canals end blindly, and are not produced into a
peripheral canal system.

26

20 THE CTENOPHORA

Famity 1. Merrensipar. The body compressed in the sagittal
plane. Sub-transverse costae longer than the sub-sagittal. Sus-Famuity 1._
MerTENSINAE. The aboral pole devoid of processes. Genera—Euchlora,
Chun ; Charistephane, Chun. Svup-Famity 2. CAaLLIANIRINAE. Body
produced at the aboral pole to form two or four processes, into which the
aboral ends of the meridional canals extend. Genera—Callianira, Peron,
with two processes ; Lophoctenia, Bourne (= Beroé, Mertens),! with four
processes. Famimmy 2. PLEvROBRAcHIIDAE. Body circular in section,
Costae of equal length. Genera—Plewrobrachia, Fleming ; Hormiphora.
L. Agassiz ; Lampetia, Chun ; Euplokamis, Chun.’

OrpeER 2. Lobata.

Body compressed in the transverse plane. The sagittal areas of the
body produced to form two more or less extensive peristomial lobes.
The ends of the sub-transverse costae produced into four lappets or

Fia. VIII.

Deiopea kaloktenota, Chun, from the transverse aspect. m, mouth; st, stomodaeum; 7,
infundibulum ; css, sub-sagittal costae ; ctr, sub-transverse costae; au, auricles; tt, accessory
tentacles ; lc, serpentiform lobular canals; zz, points where the fobuiar canals’ communicate
with the sub-transverse, meridional canals ; pp, papillae.

auricles on which the combs extend. The eight ciliated grooves are con-
tinued over the whole length of the costae. Sub-sagittal costae longer
than the sub-transverse. Transverse gastrovascular canals obsolete, a pair
of canals being given off from either side of the infundibulum. Meridional
and stomodeeal canals communicate with one another by means of prolonga-
tions of the latter, and from these connecting vessels serpentiform diver-
ticula are given off into the sagittal lobes. Tentacular sheaths absent.
Tentacles in the form of numerous accessory filaments situated in grooves
which extend from the mouth to the bases of the auricles. ,

Famity 1. Lesvgurrpar. The sagittal lobes rudimentary ; auricles
long and ribbon-like. Genus— Lesuewria, M. Edwards. Famtmy 2.

1 The four-crested Callianirid, to which I have given the name Lophoctenia, was
discovered by Mertens in 1833, and was named by him Bero#. As this generic name
belongs to another form it cannot be retained, and since no other has been suggested
I have renamed Mertens’s form Lophoctenia (Négos, a crest, and xrels, a comb),

_——

THE CTENOPHORA 21

BouiniDaE. Sagittal lobes of moderate size; lobular canals simple ;
auricles short. Genera — Bolina, Mertens; Bolinopsis, L. Agassiz ;

- Hapalia, Eschscholtz. Fasuty 3. Deioperpar. Body much compressed ;

lobes of moderate size, with lobular vessels more complicated than in
Bolinidae ; auricles short ; costae comprise very few, but very broad
combs. Genus—Deiopea, Chun. Faminy 4. EURHAMPHAEIDAE. ‘Two
wing-like projections at the aboral pole in which the sub-tentacular costae’
and meridional vessels are produced. Genus—KHurhamphea, Gegenbauer.
Famity 5. EvcHarimpar. Lobes large, with complex lobular canals ;
body covered with elongate touch-papillae ; a main tentacular filament
present, as well as accessory filaments ; above the tentacle bases are a
pair of openings which lead into elongate blind sacs lying in the sagittal
plane and ending blindly in the neighbourhood of the infundibulum.
Genus—LEucharis, Eschscholtz. Famity 6. Mnemipar. Lobes large ;
the lobes and auricles spring from near the level of the infundibulum ;
auricles long and ribbon-like. Genera—Mnemia, Eschscholtz ; Alcinoe,

Fic. IX.

Cestus veneris, Lesueur. m, mouth; tsh, tentacle sheath ; cl, c4, c5, c8, the four rudimentary
sub-transverse costae ; c?, c3, c6, c7, the four large sub-sagittal costae ; stl, st4, st, st8, the four
sub-transverse, meridional canals which communicate at x1, 22, with the sub-sagittal canals.
Rang. ; Mnemiopsis, L. Agassiz. Famity 7. CALYMMIDAE. Body much
compressed ; lobes large, springing from the level of the infundibulum ;
costae nearly horizontal. Genus—Calymma, Eschscholtz. FAmIty 8.
OcyromDaE. Lobes of great length, with relatively small attachments to
the body ; costae horizontal. Genus—Ocyroé, Rang.

OrvER 3. Cestoidea, Lesson.

Ctenophora so much compressed in the infundibular plane as to be
band-like. The sub-sagittal costae extend over the whole length of the
aboral surface ; the sub-transverse costae rudimentary. The sub-transverse
meridional canals run down the middle of the band-like body and unite
with the ends of the long sub-sagittal and stomodeal canals. Tentacle
sheath and tentacle basis present, but no main tentacle ; accessory tentacles
lie in four tentacular grooves which extend, on the oral surface, from the
mouth to the extremities of the band-like body. Gonads developed only
in the sub-sagittal canals. Famity Cestipar. Genera—Cestus, Lesueur ;
Vexillum, Fol.

22 THE CTENOPHORA

Orver 4. Platyctenea.

Ctenophora of creeping habit ; the body flattened in the principal axis
so that a dorsal can be distinguished from a ventral surface. No meridional
sub-costal canals, but a system of anastomosing peripheral vessels. Costae,
when present, retractile within ectodermal pouches. Genera—Ctenoplana,
Korotneff, costae present ; Coeloplana, Kowalevsky, costae absent; the ©
whole surface ciliated.

Fig. X.

Beroé Forskalii, Chun, from the sagittal aspect. m, mouth; é, infundibulum; so, sense
organ; pf, papilliform processes of the polar fields; ste, stomodwal canal; me, meridional
canals ; ov, Ovaries ; sp, spermaries. The peripheral canal system is seen extending over the
entire surface.

Sus-Cuass 2. Nupa. Tentacles absent.

OrperR Beroidea, Lesson.

Famity Brrorar. Elongate, conical, or ovoid Ctenophora com-
pressed in the infundibular plane, with wide mouth and spacious stomo-
daeum. ‘The otolith mass is uncovered, the polar fields surrounded by

pi oe

LITERATURE OF THE CTENOPHORA 23

branched papillae. Tentacles and tentacle sheaths absent. The meridional
canals unite with the stomodzal canals in the region of the mouth and
send out diverticula, which anastomose to form a peripheral network of
canals extending all over the body. Genus—Beroé, Brown.

LITERATURE OF THE CTENOPHORA.

. Agassiz, A. Mem. Amer. Acad. Arts and Sciences, x. 1874, p. 357.

(Embryology. )

. Ibid. Iillust. Catal. Mus. Comp. Anat. Harvard, ii., North American

Acalephae, 1865.

. Agassiz, I. Mem. Amer. Acad. Arts and Sciences, iv. 1850, p. 313.

(Beroid Medusae of Massachusetts. )

. Allman, J. Edinburgh New Philosophical Journal, N.S. xv. 1862, p. 285.
. Bethe, A. Biologisches Centralblatt, xv. 1895, p. 140. (Sub-epithelial

Nerve Plexus.)

- Chun, C. Die Ctenophoren des Golfes von Neapel. Fauna und Flora des

Golfes von Neapel, vol. i. 1880.

. Ibid. Bronn’s Thier-reichs, Bd. ii. Abth. 2, Coelenterata, 1889-1892,

p. 139.

. Ibid. Festschrift zum 70%" Geburtstage Rudolf Leuckarts, 1892, p. 77.

(Dissogony.)

. Claus, C. Arbeit. Zool. Inst. Wien. vii. 1886, p. 23. (Deiopea, Symmetry

of Ctenophora. )

. Eschscholtz, Fr. System der Acalephen. Berlin, 1829.
. Gegenbauer, C. Arch. f. Naturgeschichte, Jahrg. 22, Bd. i. 1856, p. 162.
. Haeckel, E. Sitz. der Jenaischen Gesellsch. f. Med. u. Naturwiss. Jahrg.

1879, p. 70.

. Hertwig, R. Jenaische Zeitschrift, xiv. 1880, p. 318. (Anatomy and

Histology. )

. Korotnef, A. Zeit. Wiss. Zool. xliii. 1886, p. 242. (Ctenoplana.)
. Kowalevsky, A. Mem. Acad. St. Pétersbourg, Sér. 7, tome x. 1866.

(Development. )

. Ibid. Zool. Anzeiger, 1880, p. 140. (Coeloplana.)

. Lang, A. Die Polycladen. Fauna u. Flora Neapel, xi. 1884.

. Metschnikof, E. Zeit. Wiss. Zool. xlii. 1885, p. 648. (Development. )
. Mertens, H. Mem. Acad. St. Pétersbourg, Sér. 6, tome ii. 1833, p. 479.
. Rang. Mem. Soc. Nat. Hist. Paris, iv. 1828, p. 168.

. Samassa, P. Arch. Mikros. Anatomie, xl. 1892, p. 157. (Histology.)

. Willey, A. Quart. Jour. Micr. Sci. xxxix. 1896, p. 323. (Ctenoplana.)

INDEX

To names of Classes, Orders, Sub-Orders, and Genera ; to technical terms ; and to —

aboral pole, 2
Actinians, 19
Agassiz, A., 2
Agassiz, L., 2
Alcinoé, 21
Allman, 2
ampullae, 4
Anthomedusae, 13
Anthozoa, 15
Arachnactis, 15
axis, 2

balancers, 5
balancing organ, 6
Beroé, 23
Beroidae, 6, 22
Bethe, 5
blastopore, 10
Bolina, 9, 12, 21
Bolinidae, 21
Bolinopsis, 21
breeding season, 9
Brown, P., 1

Callianira, 20
Callianirinae, 20
Calymma, 21
Calymmidae, 21
Cestidae, 6, 21
Cestoidea, 21
Cestus, 21
Chamisso, 2

Charistephane, 9, 20

Chun, 2, 8, 10, 12
Coelentera, 12, 16

Coeloplana, 16-19, 22

combs, 2, 6, 17
costae, 2, 6
Ctenaria, 18, 14
ctenes, 2

Ctenoplana, 16-19, 22

Cydippidae, 6
Cydippidea, 19

Deiopea, 9, 17, 21
Deiopeidae, 21
development, 9-12
Dissogony, 12

Eleutheria, 15
embole, 10
embryo, 10
enteron, 4, 19
eolidiform appendages, 8
epiblast, 10
epithelium, 8
Eschscholtz, 2
Eucharidae, 21
Eucharis, 9,12, 21
Euchlora, 9, 20
Euplokamis, 20
Euramphaea, 21
Euramphaeidae, 21

excretory pores, 4
Fol, 2

Gaimard, 2

| gastrovascular canals, 4

— cavity, 15
gastrula, 12
Gegenbauer, 2
gelatinous matrix, 8
gland cells, 8
gonads, 4, 9

Haeckel, E., 13
Hapalia, 21
Hertwig, R., 5
histology, 8
Hormiphora, 2, 20
hypoblast, 10

Infundibulum, 2
interstitial tissue, 8

Kolliker, 2

names of Authors discussed in the text.

Korotneff, 16
Kowalevsky, 2

Lampetia, 17, 20
Lang, A., 12, 16
larvae, 12
lasso-cells, 8
Lesueur, 2
Lesueuria, 20
Lesueuridae, 20
Leuckart, 2, 15
Lobatae, 6, 20
locomotion, 6
Lophoctenia, 20

macromeres, 10
Martens, F., 1
Medusae, 13
Mertensidae, 20
Mertensinae, 20
mesenchyme, 19
mesoblast, 9, 10
metamorphosis, 12
Metschnikoff, 2, 9, 16
micromeres, 10
Mnemia, 21
Mnemiidae, 21
Mnemiopsis, 21
mouth, 2
musculature, 8

Nemertines, 19
nephridia, 13
nerve stimuli, paths of, 6
nervous system, 5

Juda, 22

Ocyro#, 21
Ocyroidae, 21
oral pole, 2
otoliths, 5
ova, 9

INDEX TO THE CTENOPHORA

Peron, 2 sagittal plane, 3 tentacle stem, 7
Pilidium, 19 Samassa, 5, 6, 8, 9, 16 tentacles, 2, 6, 12
Planarians, 16 Selenka, 16 tentacular base, 6
Platyctenea, 22 sense organ, 2, 4, 6, 12 — filaments, 8
Platyhelminthes, 12, 18, 19 | spermatozoa, 9 — plane, 3
Pleurobrachia, 2, 20 stomach, in Coeloplana, 17 | Tentaculata, 19
Pleurobrachiidae, 20 stomodaeum, 2, 12, 19 transverse plane, 3
polar fields, 5 Stylochus, 19 — vessels, 4
Polyclada, 12, 16, 19 sub-costal canals, 4 Turbellaria, 19
pseudoblastopore, 10 sub-sagittal canals, 4

— organs, 3 ;
Quoy, 2 sub-transverse canals, 4 Vexillum, 21

— organs, 3 Volvox, 1
ribs, 2, 17
Riches, T. H., 10, 11 tentacle sheath, 7 Willey, 16, 18

Printed by R. & R. CLarK, LimiTED, Edinburgh.

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