VOL. LXI.] PHILOSOPHICAL TRANSACTIONS. 136 



and others forests to him; but likewise to remove the dirt, to seize its prey, and 

 to fasten itself to other animals of its kind, or to neighbouring bodies. 



Under the breast, and near the fore feet, is a black spot, which is the insect's 

 mouth; it is covered with a small transparent skin, which opens in the middle, 

 and shows a couple of jaws, marked with a very black spot at the place where 

 they join. Between these jaws hang very small white beards like those of the 

 tipula; and above these again, there appears a small black transversal line. 

 About the mouth there are several other little beards, somewhat in the shape of 

 feet, which are constantly in motion. 



The belly is almost as broad as the bre.ist, but has scarcely above half its length. 

 The breadth decreases towards the tail. When seen from before, the belly 

 appears composed of two conical lobes, marked in the middle with a black circle. It 

 moves alternately to, and retires from, the breast. The tail comes out between 

 these two lobes; it is of the same length with the body, and consists of 2 

 straight white and transparent canals, which are joined together till towards the 

 end, where they separate, and each terminates in 2 curved points. On the 

 back of the insect, are likewise seen 2 large round bodies, which he takes to be 

 the ovaria. 



The several hypotheses of naturalists, on the formation of shells, are knovm; 

 some will have them increase by intussusception, and others by juxtaposition. 

 This latter opinion, which M. de Reaumur patronized, and which nature seemed 

 to justify, became, in consequence, the most general; but if the friends of the 

 other system were thought to lose their cause, it was only for want of observing 

 with a sufficient degree of accuracy the operations of nature, whose variety 

 would have furnished them with instances in their favour. Our bivalve insect 

 offers one, which the desertion of the old shell and the formation of a new one, 

 in proportion as the animal grows, put beyond a doubt. The fact itself appears,' 

 not only from the observation of empty shells of different sizes, which are to be 

 met vnth in waters, and are nothing more than the spoils of our bivalve insects; 

 but, from the singular good fortune Mr. M. had, in seeing one of the animals 

 strip itself, entirely in his presence, of the membrane of its shell, and of the 

 exterior parts of its body, and show itself at last absolutely renewed. The 

 exuviae both of the shell and the animal's body were transparent as the brightest 

 crystal. The joints of the antennae, the bristles, the feet, the smallest hairs, 

 were moi'e distinguishable than in the animal itself. How infinitely small are 

 the organs, which, hid as it were in sheaths and cases, only become visible when 

 they are magnified some thousands of times! and how many are there which 

 escape the best microscope! In the clearest water that we drink, we can often 

 see with the naked eye spoils of this insect, joined to those of its shell, floating 

 along, like fine white cotton. 



