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The pearl muscles lie partly open : the inside of the 

 shell is of a pearly colour. The pearl lies in the smaller 

 end of it, at the extremity of the gut, and out of the 

 body of the fish, between the two films that line the 

 shell. This answers to the stone in other animals, 

 increasing by crusts growing over one another. Ac- 

 cordingly if a pearl be pinched in a vice, the upper 

 coat will crack and leap away. And as it is 

 now known, that the shells of fishes are formed -of 

 stony matter oozing out of their body, it is no won- 

 der if that matter when it chances to overflow, bursts 

 forth in any cavity of the body, and forms a little 

 mass, which hardening, becomes a pearl of the same 

 colour with the shell. 



Whereas all other animals take in nutriment by 

 the mouth, the muscle takes it in by the anus. The 

 part called the head though without eyes, ears, or 

 tongue, is immovably fastened to one of the shells, 

 so that it cannot receive any thing. The food of a 

 muscle is water, which as the shell opens, enters in 

 at the anus, and passing on by certain canate running 

 between the shell and the animal., is thence conveyed 

 into the mouth. 



We have lately discovered a progressive motion in 

 those shelUfish, which were supposed to be quite 

 fixed. Even oysters, which one would think wholly 

 i IB movable, if they are thrown irregularly into a vessel 

 of water, will in a while twrn themselves till the 

 smooth shell becomes uppermost: otherwise they 

 could hold no water in the concave shell for their 

 sustenance. 



Muscles can walk on the ground, which they do in 

 this manner. Lying on the flat side of their shell, 

 they thrust out a part, inform of a tongue, wherewith 

 they make little motions to the right a<id left, and 

 thereby dig a passage in the sand. In this digging 

 they drop gradually on one side, and so get the bhell 

 mounted on i*s edge ; then they stretch out the tongue 

 as far as they caii ; and rest for a minute or two en. 



