16^ 
THE GEOLOGIST. 
Neither must we take Mr. Smith's dictum nor Dr. Bowerbank's. 
AYe 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. 
What we want, in the first place, then, is a thorough definition 
from some zoologist or palaeontologist 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 angularis 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 Ventriculidae 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, 
then these few must most probably be taken out of that family, for it 
is not likely the animals which clothed such elaborated skeletons were 
— what those of sponges must be — amorphous. 
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 
every species exhibiting structure. The flints he should cut up into 
thinnish slices, or slit them through, and polish their surfaces 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 
which they were made — religiously preserved. 
