TISE FLt. 
3 ^ 
When the different members nave acquired fnfllcient 
firnmefs, the fly is ready to burft from its (lull in its 
•winged form. The covering of the chryfalis, efpecially 
of thofe who are metamorphofed in their own Ikin, feem 
to prove, by their harduds, an e fib final bar to that event. 
About the time, however, of its change, the head of the 
fly is capable of being fivolien and dilated in an unufual 
manner ; and it is by means of this dilatation that the 
fly burfts its coveting, and opens a paffage for its 
efcape. 
The food of flies is as various as their different kinds ; 
fome being fupported wholly by vegetable fubflances, 
while others are carnivorous ; and among the latter there 
are fome who only devour flefh in a Hate of putrefafiion. 
Dung, and vegetables in a fimilar bate, are the favourite 
meals of others. In the hiftory of the teirrus, we have 
already noticed that inftinft by which the females are di- 
rected to depofit their eggs within reach of food proper 
for each fpecies f. 
The female flies are all fecundated by copulation ; an 
aft in which the moft incurious obferver mull have fre- 
quently feen them engaged. The obfervations of Reau- 
mur feem to prove, that the females of fome kinds take 
that part in the act of fecundation which is ufually per- 
formed by the male in other animals; and that it is her 
extremity which penetrates into the body of the male. 
The far greater part of iufcfts are oviparous ; fome, how- 
ever, belonging to this geaus bring forth living young: 
But what appears molt unaccountable is, that foms appa- 
rently ol the fame fpecies are viviparous, while the reft 
lay 
t Page 97. 
