792 
DE. J. S, BOWEEBANK ON THE ANATOIMY 
Without the slightest appearance of nerves or muscles, it has the power of opening 
pores on any part of its surface and of closing them again at pleasure, without leaving 
a trace of their existence to indicate the spot they occupied ; and there is no amount of 
laceration or destruction that it does not seem capable of repairing or replacing in a 
very short period, reproducing itself over extensively denuded surfaces in a very few 
hours. It also shares, in common with the interstitial membranes, the power of 
strongly and quickly adhering to other sponges of the same species with which it may 
be brought in contact, but never with those of a different species, however long the two 
may remain pressed against each other. In some sponges the distal extremities of the 
skeleton pass through and project beyond the surface of the dermal membrane, while 
in other cases the whole of the skeleton is confined within it. 
I will not describe at length these remarkable powers of the dermal membrane, but 
refer the reader to a series of observations on the “ Vital Powers of the Spongiadse,” 
published in the Reports of the British Association for 1856, p. 438, and for 1857, 
p. 121, in which I have described in detail a series of observations and experiments on 
Ihdng sponges, which demonstrate in a satisfactory manner the extent of the vital powers 
and capabilities of this highly sensitive membrane. 
In some species of sponges the outer surface of the skeleton is especially modified to 
strengthen and support the dermal membrane. Thus in some of the keratose sponges 
of commerce, in parts of the sponge which have been in contact with other sponges, nr 
with rocks or stones, we find a fine network of stout fibres immediately beneath the 
derma, as represented by fig. 9, Plate XXXII. ; Isodictya varians^ Bowerbank, MS., 
is always furnished with a fine network of spicula, the reticulations consisting of a single 
series of spicula only, and on this framework the dermal membrane is firmly cemented. 
Fig. 8, Plate XXXII. represents a small portion of this dermal reticulation, magnified 
108 linear. 
In Halicliondria panicea the same description of reticulation prevails, but in this 
sponge the fibres of the network are always composed of numerous spicula cemented 
together, as represented in fig. 5, Plate XXXII., illustrating the porous system of the 
above-named species of sponge. But this regularity of structure is not constant even in 
the same individual ; thus in Hal. panicea you will often observe one portion of the 
dermis beautifully reticulated, while a closely adjoining spot "will be supported by a series 
of matted spicula without any indication of areas for the pores, and these variations in 
structure are evidently determined by the presence or absence of those organs at parti- 
cular parts of the surface. In other cases, beside a general attachment of the inner sm’- 
face of the dermal membrane to the surface of the skeleton, we find it supported by 
numerous flat fasciculi of spicula dispersed irregularly on its inner surface, and differing 
materially in size and form from those of the skeleton, as in our common British spe- 
cies, Halichondna incrustans. Great variety exists in these modes of strengthening and 
supporting the dermal membrane ; but those which I have described above will suffice 
to illustrate the general principles of their application. Beside the general systems of 
