AND PHTSIOLOaT OF THE SPONGIAD^. 
791 
In these species of Grantia there is no doubt regarding the existence of cilia, the 
whole of these great cavities being completely lined with them. 
It is a question whether the intermarginal cavities share, in common with the inter- 
stitial canals, in the function of the assimilation of nutriment, or whether they are 
devoted solely to the aCTation of the fluids of the animal ; and this, if we consider the 
structure and extent of the interstitial canals in the Halichondroid sponges, is probably 
the case. In Grantia the abundant provision of cilia in those cavities at once stamps 
them as breathing- organs ; and although cilia have never yet been satisfactorily proved 
to exist in the intermarginal cavities of the Halichondroid sponges, there can be no 
reasonable doubt of their being the homologues of the large ciliated cavities in Grantia 
compressa and other similarly constructed sponges. Now in these sponges, although 
the cilia may be readily seen in vivid action within the open oscula, as I have described 
at length in my paper “ On the Ciliary xAction of the Spongiadee,” published in the 
‘Transactions of the Microscopical Society of London,’ vol. iii. p. 137, not the slightest 
trace of cilia exists without those organs ; and this seems to indicate that the abating 
functions were strictly confined in these sponges to the large intermarginal cavities. 
The same mode of reasoning applies equally well to the intermarginal cavities of 
Geodia and Packymatisma, to which it is probable that the cilia are in like manner con- 
fined. The great valves at the proximal ends of these cavities in this tribe of sponges 
appear to strongly indicate a decided separation of the functions of aeration and diges- 
tion ; and if this conclusion be true in regard to the intermarginal cavities of Geodia 
and Pacliymatisma, it Avill probably be so in the homologous organs in Grantia ; and in 
this case we must look for the digestive surface in the shallow cavities intervening 
between the terminal valve of the intermarginal cavities and the parietes of the great 
cloaca, and of the surfaces of that organ itself. The structure and functions of the 
intermarginal cavities, and especially as displayed in Geodia and Pachymatisma, indi- 
cate a closer alliance with the great class Zoophyta than has hitherto been suspected 
to exist. In the one case we have an accumulation of individual animals conjoined in 
one mass ; in the other a similar congregation of organs in place of individuals. 
Permal Membrane. 
The dermal membrane envelopes the sponge entirely. When denuded of sarcode by 
partial decomposition, it has the appearance of a simple, pellucid, unorganized mem- 
brane. In the living state its inner surface is somewhat thickly coated with sarcode, 
and it has the appearance of, comparatively speaking, a stout, tough skin, and in many 
sponges it requires a considerable amount of violence to tear it. The dermal membrane of 
the Turkey sponge of commerce, Spongia officinalis., is abundantly supplied with primitive 
fibrous tissue. It curves round the margins of the porous areas, thickening and strength- 
ening the whole of the dermis to a very considerable extent; but it exists to a very slight 
extent in the pellucid membranes of the areas in which the pores are opened. When 
alive, it is replete with powers of life and action of a very remarkable description. 
