34)2 INSECTS. 



As, however, is commonly the case in insects, preda- 

 ceous or vegetarian habits in the one state do not imply 

 a continuation of the same habit in another, and we not 

 seldom find the predaceous larva followed by a vegeta- 

 rian Fly, and the reverse. There are, however, a few rules 

 which appear to prevail, and which are worthy of note. 



In the first division of Proboscidea, Nemocera, it may 

 generally be observed that the Blood-sucking Flies (i.e., 

 Gnats, Midges, &c.) are those which proceed from aquatic 

 larvae, the terrestrial larvae which live chiefly on fungi and 

 other plants, living or decayed, producing flower-loving 

 Flies. 



In the second division, Brachycera, on the contrary, 

 the Flies proceeding from aquatic larvae feed on the honey 

 in flowers, &c., while the blood-sucking Horsefly, the 

 predaceous Empis, and carrion-eating Flies are terrestrial 

 in the larva state. It is in this division that the para- 

 sitic larvae are found, of both kinds of parasitism, in the 

 nests and bodies of other insects, and in the bodies of 

 animals, and these larvae produce Flower-loving Flies. 



The rules just given are not to be considered as 

 without exception, even among insects whose habits are 

 known ; and it must be remembered that there is so large 

 a number of insects of whose habits in one or both states 

 we are as yet entirely ignorant, that it is impossible to lay 

 down general rules in those matters which may not here- 

 after prove to be valueless. 



The Parasitic Flies Flies, that is, which are parasitic 

 in their perfect state upon quadrupeds or birds are found 

 only in the second section, Eproboscidea, and, with the 

 peculiarities of their transformations, have been already 

 described. 



The number of the Diptera is so large, that to describe 



