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into chambers, into each of which a part of the animal is extended, 

 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 communica- 

 tion 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 dis- 

 cover the wisdom of the Almighty Creator. The conformation of the 

 inferior part of this shell shows 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 pe- 

 culiarity of conformation, than that which secures its firm adherence. 

 But the shell to which it was attached might have been likely to be im- 

 peded 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 it at its anterior part, quitting, as it advanced, 

 the posterior part; and having finished its chamber for that period, 



