95 
gives to the animal a power of raising or of lowering itself in the water, 
as its will directs. But in this shell the posterior chambers are shut up 
distinctly separate from each other, and of course have no communi- 
cation with the last, or anterior chamber, in which the animal resides. 
A slight attention only being paid to this fossil, it is probable, that 
the first idea excited respecting it may be, that its original construction 
was deficient in that astonishing adaptation of means to the ends pro- 
posed to be accomplished, which always exists in the works of nature. 
Cut off from all communication with the closed apartments which he 
had quitted, but to which he was still adherent, the animal could have 
had no power in influencing its librations in the water, and consequently 
seems to have been fastened to an useless and ungovernable incumbrance. 
But here, as in every other apparent deficiency of design in the 
works of nature, only a further extension of our inquiries is necessary, 
to discover the wisdom of the Almighty Creator. The conformation 
of the inferior part of this shell shews it to have been adherent to the 
shell of some other animal : a circumstance, indeed, which at first 
thought seems to add little to our information ; since the parasite, 
depending on the shell which supports it, for its loco-motion, seems 
to need no other peculiarity of conformation, than that which secures 
its firm adherence. But the shell to which it was attached might have 
been likely to be impeded in its own librations by an unlimited 
increase of the weight which was accumulated on it. 
To prevent the occurrence of this circumstance, the structure of this 
appendage appears to be admirably well calculated ; since the animal, 
with its shelly appendage, was, in all probability, thereby constantly 
kept at the same degree of specific gravity, through all the stages of 
the animal’s growth. The formation of these several chambers doubt- 
lessly resulted from the animal increasing the size of its receptacle, 
by lengthening and widening at its anterior part, quitting, as it 
advanced, the posterior part; &nd having finished its chamber for 
that period, shutting and sealing up so much of the hinder part of 
