750 
DE. J. S. BOWEEBAJS'K ON THE ANATOJIT 
“ I consider, however, that this difference between sponge and silk in no wise affects 
the question of the former substance being a product of the animal kingdom, which the 
other experiments, I think, satisfactorily prove.” 
In considering the results of these analyses with a view to proving the animal nature 
of the Spongiadse, the evidence afforded by the coincidence of its structural character 
and its chemical constituents with those of 8ertularia ojperculata, is still more conclu- 
sive than that derived from the chemical constituents of silk ; and, in truth, the action 
of the chemical agents on the zoophyte and the sponge, as might naturally be expected, 
are almost in perfect accordance. 
Membranous Tissues. 
These structures may be divided into two classes. 
1st. Simple membranous tissue. 
2nd. Compound membranous tissue. 
The first is a simple, apparently unorganized, thin pellucid tissue. It is evidently not 
composed of an extension of keratode, as it is rapidly decomposed after the death of the 
animal. It is found in abundance filling up the areas of the network of the skeleton 
in a great variety of sponges, and it appears to be capable of secreting sarcode on both 
its surfaces when thus situated ; on the dermal membranes the sarcode is found on the 
internal surface only. 
Compound Membranous Tissue. — These structures consist of simple membranous tissue 
combined more or less with primitive fibrous tissue. Their most simple forms exist in 
the membranes lining the interstitial cavities of the sponge, and in the dermal mem- 
branes. 
It is difficult in some cases to discriminate between this class of tissues and simple 
membranes, unless it be by the aid of their functional characters, as the compound 
tissues are frequently quite as pellucid, although not so thin, as the simple ones. 
In dermal membrane, and the membranous linings of the internal cavities of the 
sponge, they are thin and very translucent ; but on careful examination with high micro- 
scopic powers and transmitted light, with the aid of polarization, we frequently detect 
the elastic primary fibrous tissues incorporated with the structure. In the contractile 
membranes forming the oscular diaphragms in Grantia, and in those at the base of the 
intermarginal cavities in Geodia and Pachymatisma, they attain a greater degree of 
thickness, and especially in the two latter genera of sponges. In Alcyoncellum, Quoy et 
Gai^iaed, the organization of their tissue is still more complex, and we there find them 
constructed of repeated layers of membranous structure, abounding in primitive fibrous 
tissue disposed in parallel lines in each layer, the fibres disposed so closely together as to 
completely cover the membrane beneath, and the direction of the fibres being at various 
angles to the axis of the great cloacal appendages of the sponge, so as most effectually to 
aid in the contraction or expansion of that organ. They are so closely packed together 
and so intermingled, that I could not ascertain their length; but from the gradual 
