WHAT ARE THE YENTEICULITES ? 
165 
Then, and not till then, shall we have the proper data for replying 
to our question, What are the Yentrtctjlites ? 
We would say a few words on the rigidity of the ventriculites. We 
know there is a tendency amongst geologists to consider the ventricu- 
lites as of flexible structure when living. This notion, originating with 
the late Dr. Mantell, has been perpetuated by their occurrence as 
fossils in every variety of shape, apparently of dilation or contraction. 
On the other hand, it has been urged that the attachment of oyster 
and dianchora shells and serpulae prove that they must have been 
rigid, because otherwise such parasites could not have lived and 
grown on them, as the growth-lines of such shells prove them to 
have done. 
For our own part we do not see the force of either argument, for 
the apparent expansions and contractions may be, as we believe 
them, a mere accidental kind of growth of the ventriculite, which had a 
general tendency to flatten or become disk-like with age. We are 
not aware that any closer approximations of the constituent fibres 
in the so-regarded contracted specimens, or of their dilations in the 
equally hypothetical expanded ones, has ever been observed; and, 
moreover, such a complicated and hraced structure, which is pointed 
to as a wonderful example of the Creator's engineering skill to pro- 
duce a comparatively strong framework out of the slenderest ma- 
terials, would lose its apparent object, and certainly must have been 
one of the most awkward and intractable of any which could have 
been conceived for such a purpose as elasticity or flexibility. 
As to the growth of shells upon ventriculites, of all the examples 
we have seen, and they are many, most were decidedly attached to 
dead skeletons. Some few we have seen pitted by the marks of 
the corrugations and pores of the skin, and such evidently shows 
that the oyster or dianchora grew on the living ventriculite, the fry 
fixing themselves most probably, in the first instance, in the inter- 
spaces between the pores, if the ventriculite was a sponge, or between 
the tentaculated heads, if the ventriculite was a polypiferous organism. 
In some instances, and we figure an example (see fig. 1, p. 161), the 
oyster or dianchora growing for some time on the living skin, grew on 
after the death of the ventriculite ; for, if Dr. Bowerbank's theory of 
the sponge-origin of flint be true, and it certainly is the best hypothe- 
sis yet propounded, the amorphous sponge growth enveloping the 
ventriculite, and since converted into flint, was prevented growing 
over those shell-fish by the currents produced by their gills, and the 
motive action of their unattached valves in opening and closing ; conse- 
