164 



THE GEOLOaiST. 



Neither must we take Mr. Smith's dictum nor Dr. Bowerbank's. 

 We must take the evidence before us. How does this stand ? Mr. 

 Smith has seen this octahedral structure in some species and he 

 applies it to all. But he has not proved it by actual examination, 

 he has not seen it in every case. Dr. Bowerbank, who has lent us the 

 beautiful specimen of recent sponge which we figure (Plate IX.), as 

 presenting such a marvellous resemblance in its corrugations to certain 

 species of cephalites, we think, does not believe in the octahedral 

 structure occurring in all the species of ventriculites, brachiolites, 

 and cephalites ; but then we are not aware whether he or any one 

 else has ever examined, certainly no one has ever figured, the rudi- 

 mentary structures of every species of those interesting groups. 



AVhat we want, in the first place, then, is a thorough definition 

 from some zoologist or palaeontoiogist of what are the marking cha- 

 racters of a sponge. As far as we ourselves can make out, sponges 

 are amorphous animals of a globular form, or of some modification 

 of a globular form, such as funnel-shaped, stemmed with a disk-like 

 or ball-like head, or convoluted. They may even be angulated, like 

 the Guettardia angular is of the chalk group of ventriculites ; for the 

 modifications of the true sponges may be regarded as modifications 

 of the natural tendency in the true spherical sponges to form a large 

 central perforating canal, the enlargements of which or of its walls, 

 combined with various kinds of constrictions in them and the elon- 

 gation of the sponge's attachment-part into a stem, are capable of 

 giving rise to every known modification of true sponge. There is 

 nothing therefore in the various and sometimes intricate shapes of 

 the Ventriculidge to militate against their being sponges. But if 

 Mr. Smith's octahedral structure is to be met with in all, then they 

 would seem not to be sponges ; and if only some are thus constituted, 

 tlien tliese few must most probably be taken out of that family, for it 

 is 7iot likely the animals which clothed such elaborated skeletons were 

 — what tliose of sponges must be — amorplious. 



Some one of our young geologists who wants to acquire name and 

 fame should set to work collecting in flint and in chalk specimens of 

 cvrrii species exhibiting structure. The flints he should cut up into 

 thinnish slices, or slit them through, and polish their surfiices for 

 microscopic examination, and the chalk specimens should be cleared 

 out with acid, as Mr. Smith years ago did, but we regret no longer 

 does. Careful drawings of the structure of each species should be 

 made, and the evidence of their accuracy — the original specimens from 

 wliich lliev wtMv made — religiously preserved. 



