16 IXTKODUCTION. 



7. DiPTERA (^Mosquitoes, Gnats, Files, ^c). Insects 

 with a horny or fleshy proboscis, two wings only, and two 

 knobbed threads, called balancers or poisers, behind the 

 wings. Transformation complete. The larvae are maggots, 

 without feet, and -sdth the breathing-holes generally in the 

 hinder extremity of the body. Pupaj mostly incased in the 

 dried skin of the larvae, sometimes, however, naked, in which 

 case the wings and the legs are visible, and are found to be 

 more or less free or mieonfined. 



The two-winged insects, though mostly of moderate or small 

 size, are not only very numerous in kinds or species, but also ex- 

 tremely abundant in individuals of the same kind, often appearing 

 in swarms of countless multitudes. Flies are destined to live 

 wholly on liquid food, and are therefore provided with a proboscis, 

 enclosing hard and sharp-pointed darts, instead of jaws, and fitted 

 for piercing and sucking, or ending with soft and fleshy lips for 

 lapping. In our own persons we suffer much from the sharp 

 suckers and bloodthirsty propensities of gnats and mosquitoes 

 (Culicidce), and also from those of certain midges {Ceratopogon 

 and Simidium), including the tormenting black-flies {Simulium 

 molestum) of this country. The larvas of these insects live in 

 stagnant water, and subsist on minute aquatic animals. Horse- 

 flies and the golden-eyed forest-flies ( Tahanidee), whose larvse 

 live in the ground, and the stinging stable-flies (Stomoxys), which 

 closely resemble common house-flies, and in the larvEe state live 

 in dung, attack both man and animals, goading the latter some- 

 times almost to madness by their severe and incessant punctures. 

 The winged horse-ticks (HippobosccB) , the bird-flies {OrnithomyicB), 

 the wingless sheep-ticks {Melophagi), and the spider-flies {^Xycte- 

 ribia), and bee-lice (Braulee), which are also destitute of wings, 

 are truly parasitical in their habits, and pass their whole lives 

 upon the skin of animals. Bot-flies, or gad-flies ( (Estridce), as 

 they are sometimes called, appear to take no food while in the 

 winged state, and are destitute of a proboscis ; the nourishment 

 obtained by their larv^, which, as is well known, live in the bodies 

 of horses, cattle, sheep, and other animals, being sufficient to last 

 these insects during the rest of their lives. Some flies, though 



