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18,500 iQch.

This description of fibre is not an absolutely necessary
constituent of a sponge, and in many of the Halichondrace-
ous tribes it is exceedingly difficult to find even a single
straggling fibre on the interstitial or dermal tissues, while
in other genera, as in Spongia, Stematumenia^ and Alcyon-
cellumy they form an important element in the structure of
the compound membranous tissues, in which they are
closely disposed in parallel lines, occasionally giving off
branches, but never appearing to anastomose with each
other like the larger fibres of the skeleton.

These fibro-membranous tissues were described by me
in the ' Annals and Magazine of Natural History,' vol.
xvi, page 406, plate xiv, figs. 1, 3, 4, and 5, in my
description of the genus Stematumenia.

If a small portion of the dermal membrane of a young
Stematumenia be carefully removed from the surface of the
sponge, the primitive fibres will be seen projecting from
the edges of the membrane in considerable numbers \ and
occasionally they may be seen to be furnished with a
terminal bulb, the greatest diameter of which is about three
times that of the fibre. The bulbs are variable in form ;



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70 ANATOMY AND PHYSIOLOGY

sometimes they are largest at the base, or pear-shaped^
at other times regularly oval, or nearly globular. By far
the greater number of fibres exhibit no bulbs at their
terminations; those which have them are always less in
diameter than the general average of the fibres. Some-
times, Tbut not very frequentljr, the bulb exhibits faint
traces of a nucleus. On examining the dermal membrane
by transmitted light and a linear power of 666, 1 found
numerous globular cells collected in groups on various
parts of its inner surface, many of them having a well-
defined central nucleus ; and among these cells I found the
bulbs imbedded, with the fibres emanating fi'om them, and
in no respect differing in appearance from the non-fibrous
cells around them (Fig. 2B9, at, a, Plate XII). On carefully
observing a number of these bulbous fibres that had been
removed fi^m their positions on the membrane, I found
that the part of the fibre nearest to the bulb was frequently
flexuous, as if in a tender and immature condition, and in
these cases the marginal line of the fibre was continued
without the slightest break or interruption into and around
the bulb, as represented in Fig. 260, a, Plate XII. At this
period of the development the young fibre does not
measure above half the diameter of a mature one, and there
is no indication of an ultimate separation from the bulb ;
but when the fibre has attained nearly the full size the
separation is then distinctly indicated \ the basal end of
the fibre immersed in the bulb becomes hemispherical, and
a constriction appears at the junction of the fibre with the
exhausted cell. Sometimes, when thus affording indi-
cations of their ultimate separation, the cell still retains its
rotundity, but all indication of its nucleus has disappeared,
and it is perfectly transparent, as represented in Fig. 260,3,
Plate XII, while in other cases it is visible only as a
collapsed and shrivelled vesicle adherent to the hemi-
spherical termination of the fibre, as represented in Fig.
260, Cy Plate XII. I could not find the slightest indication
of bulbs amid the matted mass of fibres lying on the inner
surface of the membrane, and it was only at the torn
edges of the pieces of membrane under examination, or



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OF THE 8P0N6IADJS. 71

among the groups of cells, that the bulbs in connexion with
the fibres were to be discovered.

This form of fibrous tissue is not essentially a sponge
structure; it enters lai^ely into the composition of the
membrana putaminis, and the shell of the egg of the
domestic fowl, and I have also found it in the foliated por-
tion of a coral, Pavonia lactuca, when deprived of its
earthy matter by dilute hydrochloric acid ; and it occurs
also in the membranes of some species of Ascidians. Prof.
Bowman, in his treatise on mucous membrane, in the
' Cyclopaedia of Anatomy and Physiology,' in his descrip-
tion of the white fibrous element of areolar tissue, says,
'' Beside these bands, commonly called fasciculi, there are
some finer filaments of the utmost tenuity, which seem to
take an uncertain course among the rest/' These fila-
ments, it is very probable, are the homologues of the
primitive fibrous tissue which I have thus described.

2. Keratose Fibrous Tissue.

General character of tie keratose fibres of the horny
skeleton. — ^The essentia character of the fibres of the homy
skeleton is, that their normal form is always that of a cylinder,
while the network of the skeletons of the Halichondroid
sponges, which approach nearest in structure to that of
spicidated keratose fibre, is always more or less irregular
in shape ; and in the fully developed state generally com-
pressed to a very considerable extent ; but a careful exami-
nation of the youngest portions of the two forms of skeleton-
tissue will always render the difference in the two strucJtureb
apparent. In the spiculated keratose fibre the keratode is
always the predominant element, and the spicula the sub-
ordinate one ; while in the skeletons of the Halichondroid
sponges the spicula always predominate, and the keratode
is merely the secondary or surrounding medium. In the
former structure, in the extension of the terminations of
the skeleton, the keratode is the leading element, while in
the latter the spicula take the lead.

The fibre is formed of a succession of concentric layers.



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72 ANATOMY AND PHYSIOLOGY

its increase in diameter being apparently effected at the
external surface. Its longitudinal extension appears to be
caused by a progressive elongation of their terminations,
and new fibres are frequently to be seen pullulating from
the sides of the mature ones. In the dried state it is often
extremely rigid and incompressible, but in its natural con-
dition, notwithstanding there is frequently an internal axis
of extraneous matter or of spicula, it is often remarkably
soft and flexible. The spicula, although immersed in the
fibre, evidently possess a considerable amount of mobility
within the surrounding medium.

The colour of the fibres is always amber-yellow, varying
in different species from a very light to a deep yellow -brown
tint, and it is always semi-transparent. In the Uving state,
when the fibres happen to touch each other, whether by
their terminations or laterally, they appear at all times to
unite.

The keratose skeleton-fibres vary in their organization to
a very considerable extent, but the whole of them may be
comprised in the following nine typical forms :

1. SoUd simple keratose fibre.

2. Spiculated keratose fibre.

3. Hetro-spiculated keratose fibre.

4. Multi-spiculated keratose fibre.

5. Inequi-spiculated keratose fibre.

6. Simple fistulose keratose fibre.

7. Compound fistulose keratose fibre.

8. Regular arenated keratose fibre.

9. Irregularly arenated keratose fibre.

1 . Solid Simple Keratose Fibre.

The typical form of this description of fibre is that which
forms the skeleton of the Turkey sponges of commerce, the
structure of which I described in a paper read before the
Microscopical Society of London, and published in vol. i,
p. 42, of its * Transactions.' The mature fibre is perfectly
solid, and no vestige of a central cavity can be observed in
any part of it, either when viewed by transmitted light or



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OF THE SPONGIAD^. 73

in transverse sections of the fibre, by the aid of a Lieber-
kuhn* Occasionally, but very rarely, I have seen in young
and immature fibres faint and irregular indications of there
having been a very small central cavity in perhaps the
earliest period of its development, but in the mature fibre
I have never been able to trace such cavities (Fig. 2G1,
Plate XIII).

This description of fibre is occasionally surrounded by a
membranous sheath, on which is imbedded a beautiful
system of hollow fibrils or vessels, which sometimes wind
round the skeleton-fibre in a spiral direction ; at others it
assumes a longitudinal course, giving off short csecoid
branches; or it forms a complex and irregular network.
In an Australian sponge in my possession, the latter mode
is the only form in which it occurs. In some of these
minute fibrils or vessels I observed numerous minute
globules, which were rendered movable by a slight pres-
sure on the glass under which they were exhibited. The
mean diameter of these tubes or vessels was ^ inch. This
tissue is of rare occurrence, and I have been unable to de-
termine whether it is a specific character, or whether it is
due to a peculiar condition of the sponge. Fig. 279,
Plate XVI, represents a portion of fibre from the skeleton of
one of the sponges of commerce. Fig. 280, Plate XVI, is
from a rigid species of Australian sponge. This singular
tissue is described more fully in a paper which I read
before the Microscopical Society of London in 1841, and
which is published in their * Transactions,' vol. i, p. 32,
plate iii.

2. Spiculated Keratose Fibre.

This structure is essentially a solid form of keratose
fibre, no central cavity ever being visible in its axis. The
normal form of the fibre is cylindrical, but it is occasionally
more or less compressed, and always contains a thin central
line or axis of spicula arranged in longitudinal series. The
spicula are secreted within the fibre, and are nearly imiform
in size^ and always of the same shape in the same species



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74 ANATOMY AND PHYSIOLOGY

of sponge. In the production of the young fibres, the
projection of the new keratode and the secretion of the
new spicula appears to be simultaneous. In this class of
structure the keratose fibre is the predominant element,
and the spicula the subordinate one, and we accordingly
frequently find the fibres destitute of spicula for short dis-
tances ; but these occurrences are the exceptions, and not
the rule of the structure. Fig. 262, Plate XIII, represents a
portion of a longitudinal section of the skeleton of Halu
chondfia oculata, Johnston {Chalina^ Bowerbank).

The mode of the progressive development of this form of
fibre is interesting. In a young specimen of Chalina
Montaffviy Bowerbank, I observed that when a new fibre
was projected from the skeleton it usually contained a
single spiculum, thinly covered by keratode at the apex,
and more thickly so towards the basal end. Another
spiculum followed the first, the terminations of each over-
lapping the other; and at the junction of the two the
keratode was accumulated in the form of a plumber's joint,
as represented in Fig. 263,Plate XIII, so as to give additional
strength to the junction of the spicula, while the middle
portion of the second spiculum remained very thinly
covered by keratode. When the distal end of the new
fibre has attained its proper length, or has become cemented
to the side of another fibre, the remaining portion of the
keratode 4s produced, and the fibre then assumes a regular
cylindrical form.



3. HefrO'Spiculated Keratose Fibre.

This form of fibre has a somewhat irregulw' axial series
of spicula, with occasionally exter-axial ones disposed in
accordance with the axial spicula, and others at intervals at
right or nearly right angles to the axis of the fibre. The
only sponge in which I have found this form of fibrous
tissue is Diphdemia vesicula, Bowerbank, from deep water,
Shetland. Fig. 273, Plate XIV, represents a portion of a
skeleton-fibre.



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OF THE SPONOIABiE. 76



4. Multi-spiculaied Keratose Fibre.

This description of fibre is literally a cylindrical mass of
spicula cemented together by keratode, and surrounded by
a thin case of the same substance. The spicula are
exceedingly niamerous, and very closely packed in parallel
lines in accordance with the axis of the fibre. They are
nearly uniform in size, and always of the same shape in the
same species of sponge. In this structure the spicula are
the predominant element, and the keratode the subordinate
one. Fig. 264, Plate XIII, represents a fibre fi-om the
skeleton of Desmacidon affagfropila, Bowerbank.

5. Inequi'Spiculated Keratose Fibre.

This form of fibre is composed of an infinite number of
spicula disposed in every possible direction, cemented
together by keratode, and surrounded by a sheath of the
same material. The spicula agree in form in all parts of
the sponge, and are nearly of the same size. In these
fibres the spicula are the predominant element, the keratode
the secondary one. In the only sponge in which this form
of structure has yet been found, Baphyrua Griffithii^
Bowerbank, the fibre is very unequal in size and much
varied in its form, frequently becoming very much fiattened
and expanded. Fig. 265, Plate XIII, represents a longi-
tudinal section of a small portion of a fibre from the
skeleton, showing the irregular disposition of the spicula
within it.

6. Simple Fisftdose Keratose Fibre.

This form of fibre is usually very much larger and more
rigid than the soUd keratose fibre. It is cylindrical, and
continuously fistular. The great central cavity of the fibre
usually occupies about one third of its diameter. It is
nearly uniform in its size, but occasionally it is dilated
considerably for a short space, and then resumes its original



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76 ANATOMY AND PHYSIOLOGY

diameter. In the young state the cavity is as large, or
nearly so, as in the adult fibres, while the enveloping
keratode assumes the form of a thin, transparent amber-
coloured coat, which in the mature state becomes frequently
twice or three times the thickness of the diameter of the
central cavity.

This great fistular space is lined with a thin pellucid
membrane, which, in specimens that have been dried,
appears to have been thickly covered with minute semi-
opaque granules. At the time of my first description of this
form of fibre, published in the 'Annals and Magazine
of Natural History,' vol. xvi, p. 403, I believed that in
the natural condition of the fibres the central cavity was an
open tube, but subsequent observations on specimens which
have never been dried have led me to the conclusion that
the whole of the central space is filled with a minutely
granulated substance, which presents all the characteristics
of sarcode.

There is no communication between the great central
fistular canal and the interstitial cavities of the sponge, the
projecting ends of the fibres of the skeleton being always
hermetically sealed. Fig. 266, Plate XIII, represents a
fibre from the specimen of Spongia fistularis, Lamarck, in
the Museum at Edinburgh, given to rne by Prof. Grant.

7. Compound Fistulose Keratose Fibre.

In its external characters this description of fibre is not,
under ordinary circumstances, to be distinguished from
the simple fistulose fibre, and it is only when submitted to
a microscopical power of about 100 linear that its peculiar
character can be detected. We then find that the fibre is
not only furnished with a large continuous central cavity,
but that it also has numerous minute csecoid canals
radiating from the central one at irregular distances, at
nearly right angles to its axis. These secondary canals are
very unequal in length, and very few of them reach to near
the external surface of the fibre, and none of them appear
to perforate it. Their direction, is usually in a straight



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OF THE SPONGIADiE. 77

line from the parent canal; a few assume a tortuous
direction, and a still fewer number bifurcate or branch.
Within the central tubes of the fibres there are frequently
one or two minute simple tubular fibres ; when more than
one they do not unite, but they divide and traverse each
a separate cavity, when they happen to reach one of the
anastomosing points of the great skeleton-fibre. The
structures ai^e described more at length in the ' Annals and
Mf^azine of Natural History,' vol. xvi, p. 405, under the
head of " Auliskiay' a new genus of sponges, founded prin-
cipally on the compound fistulose structure of its skeleton-
fibres. Fig. 268, Plate XIV, represents a portion of com-
pound fistulose keratose fibre as seen with a linear power
of 100. Fig. 267, Plate XIII, a portion of a similar fibre
under a power of 300 linear.

8. Regular Arenated Keratose Fibre.

This description of fibre under ordinary circumstances
has very much the appearance of simple fistulose fibre, but
when examined by transmitted hght with a linear power of
about 100 we find in the centre of the fibre a series of
grains of extraneous matter, occupying the place of the
large continuous canals of the fistulous forms of fibre.
The series of extraneous matters is not always con-
tinuous, and when an interruption takes place the fibre
becomes soUd, or faint traces only of a central cavity remains.
The mode of the inclusion appears to be due to the extreme
terminations of the young fibres being viscid, and thus
seizing on any extraneous particles that happen to come
in contact with them. The growing keratode quickly
envelopes them, and, proceeding on its course of extension,
seizes in like manner on other particles of sand or solid
matter, and thus a continuous and regular chain of extrane-
ous material is imbedded in the axis of the fibre, as repre-
sented by Fig. 269, Plate XIV. This description of fibre
is found in a great variety of keratose sponges, and especially
so among the coarse rigid skeletons of the Australian species.
And among the flexible sponges, as represented by Fig. 269.



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78 ANATOMY AND PHYSIOLOGY



9. Irregular Arenated Keraiose Fibre.

I have described this form of fibre m a paper descriptive
of two species of Dyaidea, read at the Microscopical Society
of London, Nov. 24, 1841, and subsequently published in
vol. i, p. 63, of their * Transactions/

The adult and fully produced fibre is frequently half a
line or more in diameter. It is built up in all parts of its
substance, of grains of extraneous matter, each one being
separately enveloped in keratode. The adhesive power in
the young progressing fibre not being confined to its apex
only, its sides also seize upon the surrounding grains of
soUd matter, and the keratode speedily passing round and
enveloping them, the whole fibre becomes a soUd cylinder
of irregularly imbedded molecules. There is a great variety
of substances imbedded in these fibres, dependent, as a
matter of course, on the amount of material surrounding
them at the period of their development. The skeleton of
JDyddea fragUiSy Johnston, a British species very common
on the south coast of England, presents one of the best
types of this form of fibre. And single grains of sand are
frequently to be found among the fibres of the surface of
the sponge, elevated on short pedicels of the rapidly grow-
ing young fibres, sometimes entirely, and at others only
partially, enveloped by the progressing keratode. Figs. 270,
271 and 272, Plate XIV, represent portions of fibre from
the same individual.

This genus of sponges appears, to the best of my
knowledge, to be the only animals that construct an inter*-
nal skeleton almost entirely of extraneous matter.

Siliceom Fibre.

This structure is widely different from any of the keratose
fibres which contain either secreted silex in the state of
spicula, or extraneous silex in the form of sand. The
whole substance of the skeleton-fibre consists of soUd silex,
secreted and deposited in concentric layers, exactly after



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OP THE SPONGIADiB. 79

the manner of the secretion of pure keratode in the fibres
of the sponges of commerce. When cleansed from the
sarcodous matter by which they are surrounded in a living
state, the fibrous skeleton bears a striking resemblance to
fibres of spun glass, and is quite as pellucid and colourless
as the artificial material, and the dead sponge quite as
brittle. The fibrous skeleton of Bactyhcalyx pumicea^
Stutchbury, in its mode of arrangement strikingly resembles
that of one of the sponges of commerce ; it is equally com-
plex and irregular in its structure^ and the component
fibres quite as much anastomosed. In that species the
fibres are smooth and cylindrical, but in others they
frequently abound with minute, obtuse, wart-like elevations.

There is every indication in the skeletons that the increase
in diameter, and the extension in length in the fibres, is
effected in the same manner as in the soUd keratose fibres.
The free terminations of the young fibres have the same
attenuated but obtuse form, and the pullulation of the
young fibres from the sides of the mature ones is quite as
apparent as in their keratose congeners, but they never
appear to be in the young state, as the keratose ones fre-
quently are, viscid \ and extraneous matters are never
detected at their apices, or on their substance.

There are two distinct forms of this class of fibre :

1st. Solid siliceous fibre.

2nd. Simple fistulose siliceous fibre.

The structure of solid siliceous fibre is very similar to
that of solid keratose fibre. Occasionally there are indica-
tions of a former existence of a minute central canal ; but
in the frilly developed fibre this is rarely visible. The
external characters of these fibres vary in each species. In
a new siliceous sponge in the British Museum, designated
by Dr. Gray M'Andrewaia azoica, the fibres are quite
smooth, as represented by Fig. 274, Plate XV. But in
the greater number of species they are more or less tuber-
culated, as in Fig. 275, Plate XV, which represents a group
of fibres from the type-specimen of Bactylocalyx pumicea^
Stutchbury, a portion of which is in the possession of Dr.
J. E. Gray. In other species in my possession the tuber-



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80 ANATOMY AND PHYSIOLOGY

dilation is very strongly produced, as represented in a few
fibres of Dactvlocalyx Prattii, Bowerbank, MS., Fig. 276,
Plate XV.

Of the second form, simple fistulose siliceous fibre, I know
but one example, and that is the remains of the siliceo-
fibrous sponge, Farrea occUy Bowerbank, MS., on which
the beautiful specimen of EuplecteUa cummer, Owen, is
based.

The tubulation of the skeleton-fibre is very similar to
that of some varieties of simple fistulose keratose fibre, but
the central cavities are not so invariably continuous as in
the keratose varieties of fistulose skeleton-fibre. Fig. 277,
Plate XV, represents a small piece of the spinulated simple
fistulous fibres of the skeleton of Dr. Arthur Farre's speci-
men. The spinulation of these fibres is a remarkable cha-
racter. It is the only case of the production of acute spines
on the skeleton-fibre of a siliceo-fibrous sponge with which
I am acquainted.



Prehensile Fibres.

In the course of my examination of the fibrous skeleton-
tissues, I have found but one instance in which they have
developed prehensile organs to assist in the attachment of
the sponge, and this in a minute siliceo-fibrous species,
parasitical on the base of a specimen of Oculina rosea^ from
the South Sea. In this sponge the basal fibres curve down-
ward in the form of numerous small, nearly semicircular
reversed arches, fi-om the lowest portions of each of which
there is a short stout portion of fibre projected, and at
about the length of its own diameter downwards a ring of
stout prominent bosses, six or eight in number, is produced,
very considerably increasing its diameter at that part ; im-
mediately beneath which the fibre is attenuated to a point.
These singular organs are admirably calculated to penetrate
the porous cavities or fieshy envelopes of the coral, and
thus to securely attach the sponge to its adopted matrix
(Fig. 278, Plate XV).



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OP THE SPONGIADiE. 81



CELLULAR TISSUE.

The cellular structures in the Spongiadae are few and
very simple in form. We find no series of conjoined cells
in the body of the sponge, as in vegetable tissues. The
only forms in which true cellular structures occur in the
bodies of sponges, are those of detached spherical molecular
cells, and of discoid or lenticular nucleated cells. The first
forms are found in abundance on the fibres of many species
of the true sponges, and are believed by Dr. Johnston to
be the reproductive organs of that genus. They are very
minute, not exceeding jj^^ inch in diameter. They are
peUucid, and aflbrd no indications of a nucleus, either single



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