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anything resembling them. But that such bodies do occur
in some species of Tethea appears to be the case, Professor
,Huxley having described and figured bodies which he
believed to be spermatozoa in a paper published in the
'Annals and Mag. Nat. Hist.' Second Series, vol. vii, p 370,
plate 14, as occurring in a species of Tethea found in one
of the small bays in Sydney Harbour, Australia. The
gemmules represented by Fig. 343, Plate XXV, consists of
(a) one of the larger and supposed proUfic gemmules, and (b)
one of the presumed male gemmules in situ, X 108 linear.
Wherever the former occurs, the latter appear always to
accompany them in the proportion of about two or three to
one. They are not seated like the ovaria of Geodia at the
surface of the sponge, but are always found on the inter-
stitial membranes at a considerable depth within the
sponge. The immersion of the specimen in Canada balsam
Ms rendered the marginal lines of the gemmules undis-
tinguishable from the surrounding sarcode, but their
natural boundaries would be just beyond the extreme
points of the spicula.

Fig. 344, Plate XXV, represents one of the larger gem-
mules in its natural condition and separated from the
sponge, by direct light and a linear power of 50.

The reproductive bodies in the Tethea, described by
Professor Huxley, do not resemble those in T cranium ;
no spicula are either described or figured as existing in
them, and in these respects they appear much more to
resemble the reproductive organs described by Dr. Grant
as existing in the Halichondraceous sponges of the Firth of
Forth. But I am not surprised at this discrepancy, as in
Tethea simillima, Bowerbank, MS., in the collection of the
Royal College of Surgeons, from the Antarctic regions of
the South Sea, a species very closely resembling T cranium,
the gemmules are so like those of the latter species as not
to be readily distinguished from them in their natural con-
dition ; but. when microscopically examined, not the shght-
est trace could be found of the smaller, and what I con-



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OF THE SPONGIADiB. 149

ceived to be the male gemmule in T. cranium. I have
several other species of Tethea in my possession, but I have
not yet found gemmules in the interior of any of them.

EXTERNAL GEMMULATION.



In Tethea lyncurium we have gemmules produced ex-
ternally^ which are perhaps much more entitled to that de-
signation than any of the reproductive organs previously
described. The fasciculi near the base of the Tethea are
protruded considerably beyond the surface of the animal,
and at the termination of each there appears a small mass
of sarcode, which assumes a more or less globular form. If
their bodies be immersed in Canada balsam and examined
microscopically, they will be found to contain not only the
spicula projected from the parent, but a second series,
which have been secreted in the mass which have assumed
the mode of disposition so characteristic of the skeleton of
the parent Tethea. I am indebted to my late friend Mr.
T. H. Stewart for this interesting fact, and for the speci-
mens illustrating it. They were found in Plymouth
Sound.

Fig. 342, Plate XXV, represents one of these gemmules
with a portion of the skeleton fasciculus on which it is pro-
duced, under a linear power of 60.

PKOPAGATION BY SARCODOUS DIVISION.

The fact of the resolution of the sarcode of the interstitial
tissues of Spongilla into small masses of unequal size and
variable form has long been known to naturalists, and that
when separated from the parent body each becomes capable
of locomotion, and of ultimately becoming developed into a
perfect sponge. Carter, in his valuable paper published in
the ' Journal of the Bombay branch of the Royal Asiatic
Society,* No. 12, 1849, has given a minute account of their
structure and motions when separated from the species
which form the subjects of his paper, and his descriptions
are in perfect accordance with the similar bodies separated



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150 ANATOMY AND PHTSIOLOGY

from our European species S.JluviatiliSy which I have had
frequent opportunities of observing, and of confirming the
history given by him of their locomotive powers and con-
tinual inherent motions. The author designates these
bodies " sponge-cells," and treats of them as if they had a
well-defined cell-wall, while their eccentric changes of fona
are perfectly inconsistent with such a structure. Lieberkuhn,
in treating of these bodies under the name of motile spores,
states that he has never succeeded in discerning a *' cell-
membrane " around these particles, and my own observa-
tions are in perfect accordance with his experiences. The
truth. appears simply to be that any minute mass of sarcode,
whether separated voluntarily or involuntarily, has inherent
life and locomotive power, and is capable of ultimately de-
veloping into a perfect sponge ; and in the course of this
process the dermal membrane is produced at a very early
period, and this, surrounding an agglomeration of minute
masses of sarcode, may have been mistaken by Carter for a
cell membrane. The same author, in his observations
* On the Species, Structure, and Animality of the Fresh-
water Sponges in the Tanks of Bombay,' states " that when
the transparent spherical capsules which contain the granules
within the seed-like bodies are liberated by breaking open
the latter under water in a watch-glass, their first act is to
burst ; this takes place after the first thirty-six hours, and
their granules, which will presently be seen to be the true
ova of a proteaniform infusorium, varying in diameter from
about the ^^th part of an inch to a mere point, gradually
and uniformly become spread over the surface of the watch-
glass. On the second or third day (for this varies) each
granule will be observed to be provided with an extensible
pseudo-pediform base ; and the day after most of the largest
may be seen slowly progressing by its aid, or gliding over
the surface of the watch-glass in a globular form by means
of some other locomotive organs.''

This description is strikingly similar to the same author's
account of the masses of sarcode separated from the sarco-
dous lining of the interstitial canals of Spongilla ; but it
must be observed that, in the development of the egg, the



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OP THE SPONGIAD^. 151

first act is to liberate itself from the membranous envelope ;
and the contents thus hatched become moving masses of
free sarcode, but without the locomotive cilia that are found
on the so-called ova or gemmules of the marine sponges, so
minutely and accurately described by Dr. Grant in his
papers *' On the Structure and Functions of the Sponge " in
the ' Edinburgh New Philosophical Journal/ vol. ii, p. 129.
This author describes the ova or gemmules of Hcdichondria
panicea {HaL incrustans, Johnston), after having floated
freely about for a period by means of the cilia around its
larger extremity, as attaching itself to a fixed body by its
smaller end and then gradually settling down in the form of
a broad flat mass, and after losing its cilia being gradually
developed in the form of the parent sponge. Thus every
description by these close and accurate observers tend to
the conclusion that the multiplication of the sponge is
efiected by the origination in the ovum, or by the agglome-
ration in the form of gemmules, of particles of sarcode.
The action of the minute masses of sarcode liberated by the
bursting of the envelope of the ovum, and their subsequent
development, is precisely that of the so-called sponge-cell
liberated from the mass of the sarcode lining the interstices
of the sponge, and of the gemmules described by Grant
when sessile ; each moves independently at first ; each unites
with its congeners into one body : and the results, both in
means and end, are precisely the same, but their origin is
different. The one is a generation of sarcode within a
proper membrane in the form of an egg, while the others
are the production of a gemmule by independent growth,
or by spontaneous division of the sarcodous substance of
the sponge.

Both these modes of propagation occur in the same
species, Spongilla Jlwoiatilu^ but I have never yet seen them
both well developed in the same individual. Where the
ovaria were abundant, the sarcode appeared even and con-
sistent in its stiiicture, and, on the contrary, if it exhibited
manifest symptoms of granulating, very few or none of the
ovaria could be detected. This double means of propaga-
tion is by no means uncommon among the Zoophytes.



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162 ANATOMY AND PHYSIOLOGY

I have never seen the spontaneous granulation of the
sarcode in any living marine species of sponge ; but as the
vital powers and general physiological characters of that
subtftance appear to be the same in all the Spongiadse^ how*
ever varied in form and structure, it is highly probable that
perpetuation by spontaneous or accidental separation of
minute masses of sarcode is by no means confined to
Spongilla ; and from the concurrent testimony of all who
have investigated the subject, that every molecule of sai'oode,
however minute, has inherent vitality, and the power of
uniting with its own congeners whenever they may chance
to come in contact.



GROWTH AND DEVELOPMENT OP SPONGES.

The growth of the sponge does not appear to be con-
tinuous, but periodical, as we may observe in the branching
species, and especially in Isodictya palmata, Bowerbank.
If the sponge be held up between the eye and a lighted
candle, as many as five or six of the former pointed termi-
nations of the sponge in succession, from near the base to
the apex, may be seen ; and the former lateral boundaries
are also equally distinct, the oscula being most frequently,
but not always, continued through the new coating of the
lateral development of the spongeous structure. New
branches are also frequently thrown out during the last
period of development at various parts of the stem, where
no indication of branches existed previously. In all these
newly-developed parts, it may be observed that the primary
lines of the structure of the skeleton, or those radiating at
nearly right angles to the axis of the sponge, are those
which are first developed ; and at the extreme points of the
branches they are frequently seen projecting for, compara-
tively, a considerable distance in the form of single unsup-
ported threads or filaments ; but as we trace these lines
inward, we find the secondary, or connecting fibres increas-
ing in number, and the network becoming closer and more
fuUy developed. The same mode of development may be



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OF THE SPONGIADiE. 158

traced in Chalina oculatuy but not to such an extent as in
Isodictya palmata. In the sessile massive species of Hali-
chondroid sponges the same mode of development seems to
obtain, as I have frequently traced the different stages of
growth in sections at right angles to the surface of the
sponge.



ON THE CLASSIFICATION OF THE SPONGIAD^.

While the arrangement of other subjects of natural
science has occupied the attention of some of the most
laborious aud talented naturalists of every age, the Spong-
iadae appear to have scarcely attracted sufficient attention to
have excited any writer on natural history to a serious
attempt at a systematic classification. This neglect has not
arisen from any incapacity for a definite arrangement on the
part of the Spongiadae, as the organic differential characters
of the numerous groups into which, by careful examination,
they may be readily divided are as varied and as widely
removed from each other as are the strikingly distinct and
well defined divisions of the Corallidaj, and the number of
species I believe to be very much greater than those of the
latter class. Of British species alone I am already ac-
quainted with more than 160, and new ones are continually
being discovered by the aid of the dredge. It becomes
therefore a matter of necessity that we should classify their
permanent varieties of structure, and found on them a series
of orders, suborders and genera, and through these sub-
divisions become enabled to recognise more readily the very
numerous species of these animals which abound in all parts
of the world.

De Blainville proposed to include the whole of the
Spongiadae under the designation of Amorphozoa ; but this
term is objectionable, as all sponges cannot be considered
as shapeless, on the contrary many genera and species
exhibit much constancy in their form. Neither can the
term be justly applied to their internal structure, as we find



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154 ANATOMY AND PHYSIOLOGY

in Grantia, Geodia, Tethea, and other genera, regular and
systematical structures which are very far removed from
shapelessness. I have therefore thought it advisable to
adopt Dr. Grant's designation of Porifera, a term which
embraces the whole of the Spongiadse, and which is truly
descriptive of the most essential general action of the
animaPs power and mode of imbibing niitriment, which in
every species with which I am acquainted is, by a series of
minute pores, distributed over the external membrane of
the sponge.

Besides this universally existent character there are others
which are strikingly characteristic of the class, although not
so universally prevalent as the porous one. Thus the
skeletons of the Spongiadse are always internal, but in the
material and mode of construction they vary to a very con-
siderable extent. Sponges may therefore be defined as
fixed, aquatic, polymorphous animals ; inhaling and imbib-
ing the surrounding element through numerous contrac-
tile pores situated on the external surface ; conveying it
through internal canals or cavities, and ejecting it through
appropriate orifices ; having an internal flexible or inflexible
skeleton, composed of either carbonate of lime, silex, or
keratode ; with or without either of these earthy materials.
Calcareous skeletons . always spicular. Siliceous skeletons
either spicular or composed of solid, laminated, and con-
tinuous siliceous fibre.

Propagation by ova, gemmulation, or spontaneous division
of its component parts.

Dr. Grant, in his learned and elaborate ' Tabular View
of the primary divisions of the Animal Kingdom,* published
in 1861, has divided the Porifera into three orders, based
on principles which I have adopted. The first order is
Keratosa, in which the skeletons are essentially keratose
and fibrous; the second, Leuconiday is composed of the
calcareous sponges ; and the third, Chaiiniday consisting of
the siliceous sponges. I have not adopted the full and
precise definition of each of these Orders as given by the
learned Professor, as, if the whole of the distinctive cha-
racters in the first and third of them were insisted on in



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OP THE SPONGIADiE. 155

the detennination of the orders to which many exotic
species belong, it would lead in numerous cases to inex-
tricable confusion. The terra Leuconida is also objection-
able, as all calcareous sponges are not white, and colour is
at best but a very uncertain character even in the determi-
nation of a species ; I have therefore adopted the principles
of the arrangement of Professor Grant, with the following
modifications of position and descriptions of the charac-
teristics of each order.

1. Calcarea. Sponges the skeletons of which have as
an earthy base carbonate of lime.

2. SiLiCEA. Sponges in which the earthy base consists
of siliceous matter.

3. Keratosa. Sponges in which the essential base of
the skeleton consists of keratose fibrous matter.

While thus assuming the principles of arrangement
enunciated by the learned Professor, I have been induced
to vary the mode of the disposition of his Orders from the
following considerations.

In the highest vertebrated animal types we invariably
find the skeleton principally composed of phosphate of
lime with a small portion of carbonate of lime and other
substances, the whole consolidated by cartilage. As we
descend the scale of the Vertebrata we find the salts of
Ume decrease in proportional quantity until they occur in
minute detached patches only, and cartilage becomes the
essential base of the skeleton.

In the great tribe of MoUusca we find carbonate of lime
prevailing in their shells to the exclusion of phosphate of
lime, and in the compound Tunicata we have a structui*e
analogous to that of the cartilaginous tribe of Fishes. In
the massive subcartilaginous body of this tribe there is no
continuous or connected earthy deposits. This material of
the skeleton exists only in the form of detached masses of
radiating spicula. As we descend in the animal scale we
find carbonate of lime entirely absent, and silex replacing
it in the elaborate and beautifully constructed loricae of the
marine and freshwater infusoria.

If we are to reason from these gradations of structure



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156 ANATOMY AND PHYSIOLOGY

and apply our reasoning to the Spongiadae, we should then
give precedence to the calcareous sponges as representing
in the class the highest order of secretive power ; and if
we add to these considerations the regularity of structure
and function and the full development of cihary action that
exists in Grantia cUiata and compressa and the allied
species, I think it scarcely allows of a doubt that this order
should take precedence of the others in an arrangement of
the Spongiadae.

The siliceous sponges naturally follow in succession, and
the Keratosae, from their imperfect secretive powers and
their low order of organization in other respects, would
indicate their position to be the last in the series.

ON THE GENERIC CHARACTERS OP THE SPONGIAD-ffl.

The foundation of the genera of the Spongiadae has
hitherto been based principally upon form and other
external characters of an equally unstable description, and
in many instances genera have been named without the
slightest attempt to characterise them. As a generic
character form is inadmissible, inasmuch as each variety of
it is found to prevail indiscriminately in genera differing
structurally to the greatest possible extent.

I will not enter on the history of the genera that have
been proposed by previous writers on the Spongiadae, as
the greater portion of those which have been published will
hereafter be found to have been adopted, with certain
revisions of their characters, in the series of genera I pro-
pose to establish, but I shall beg to refer such of my readers
as may be desirous of further information on that subject
to page 70 of Dr. Johnston's admirable introduction to his
' History of British Sponges and Lithophytes.'

Having thus rejected form and other external characters
as the foundation of generic descriptions, we naturally
resort to the anatomical peculiarities of the animal for these
purposes ; and here fortunately we find a variety in struc-
ture and form, and a constant adherence to their respective
types that admirably adapt them to our purpose.



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OF THE SPONGIADiB. 157

If any portion of the animal remains, whereby we may
recognise it as one of the Spongiadae, it is always the skele-
ton, and it is therefore advantageous to adopt this most
persistent portion of the animal as the foundation of our
generic descriptions. But this is not the sole reason for
such a conclusion, as it is not only the most enduring por-
tion of the animal, but it is also the most undeviatingly
regular in the form and arrangement of its component
structures. However great may be the variations that
exist in size and form between different species of the same
genus, or between individuals of the same species, the cha-
racteristic tissues of their skeletons are always found to
harmonise in their structural peculiarities. It appears,
therefore, advisable in these animals, as well as in the
higher classes, to select the skeleton as the primary source
of generic distinctions. Other portions of the permanent
organs may be occasionaUy resorted to when necessary as
auxiliary characters, such as the incurrent and excurrent
canals, the intermarginal cavities, the cloaca, and the
various modes of reproduction. Bach of these characters
are of use in generic descriptions to a certain extent, but
none of them are absolutely necessary to the determination
of a genus, and occasionally we find one or more of these
modes of organization entirely absent; we may therefore
consider them not as primary^ but rather as secondary or
auxiliary generic characters.

I therefore propose to consider the varieties in the con-
struction of the skeleton as the foundation or primary
source of divisions into genera, and to dedicate that portion
of the animal especially to that purpose ; the auxiliary or
secondary characters being resorted to only when required
to aid and assist the primary ones ; and it is only to a very
Kmited extent that they are in reality available. Thus the
cloaca in the Order Calcarea becomes a very important
means of generic distinction, and in some cases in the
Order Keratosa it is also a prominent character, while in
Silicea it is generally absent. In some species of this
order, as in JjcyonceUumy Polymaatiay and Halyphyaema^ it
assumes a normal character, while in several species of



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n



158 ANATOMY AND PHYSIOLOGY

Halichondria, and in H. panicea, it assumes very striking
proportions in excessively developed specimens, whilst in
others it is either an occasional, uncertain, and progressive
organ, or is altogether absent.

The mode of propagation is also an uncertain character.
Thus in Tethea cranium we find it to be by internal gem-
raulation ; in T, lyncurium by external gemmules ; and in
other species of the genus no gemmules of any description
have hitherto been detected. In Geodia, Pachymatisma,
and Spongilla the general structure and mode of disposition
of the ovaria render them valuable auxiliary generic cha-
racters, but in other cases they are of little or no value.

The intermarginal cavities are available as generic cha-
racters in Geodia and the nearly allied species, and in the
same sponge the relative position of the connecting spicula
form good distinctive characters in the genera Geodia^
Ecioneniia, and also some of the sihceo-fibrous sponges.
In Alcyoncdlum, Polymastia, and Geodia the position and
appendages of the oscula are also available, but generally
speaking those organs are so mutable as to render them of
little value as generic characters.

The following tabular view of the arrangement I propose
to adopt, will perhaps render the details regarding the dis-
tinctive characters and natural affinities of the genera more
readily comprehensible.



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OF THE SPON6IADJE.



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160 ANATOMY AND PHYSIOLOGY



Order I. CALCAREA.



The number of species of calcareous sponges that are
known are comparatively so few, and the four genera into
which I have divided them are naturally so well charac-
terised as to render the establishment of suborders unne-
cessary. Hereafter, when we are acquainted with a greater
number of species and other varieties of organization
become known, the genera now established may become
the types of suborders, for which oflSce their distinctly
different modes of construction render them eminently
eflScient.

Although the calcareous structure of the species of this
order appear to entitle it to precedence in the arrangement
of the Spongiadae, it does not maintain in the structure of
its skeleton throughout the whole of the genera the same
high type of formation that is exhibited in Grantia com-
preamy Johnston, and the allied species, and we observe a
progressive decline in regularity of structure in its genera
very analogous to what we find existing among the Hali-
chondroid tribe of sponges ; but in this respect they only
follow the same laws of gradual degradation that obtain in
every other class of created beings, and this gradual decline
in regularity of structure shoiJd not therefore miUtate
against the claim of even the lowest in organization of the
tribe from taking precedence of the siliceous sponges.

Dr. Grant was the first naturalist who decided that the
spicula of a certain group of small sponges were composed
of carbonate of lime, and he separated them accordingly


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Online LibraryJames Scott BowerbankA monograph of the British Spongiadæ → online text (page 15 of 25)