16 
INTKODUCTION. 
7. Diptera (^Mosquitoes^ Gnats^ Flies^ 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 with the breathing-holes generally in the 
hinder extremity of the body. Pupae 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 unconfined. 
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 
( CuUcidce), and also from those of certain midges ( Ceratopogon 
and Simulium), including the tormenting black-flies {Simiilium 
molestimi) of this country. The larvae of these insects live in 
stagnant water, and subsist on minute aquatic animals. Horse¬ 
flies and the golden-eyed forest-flies {Tahanidce), whose larv^ae 
live in the ground, and the stinging stable-flies {Stomoxys), which 
closely resemble common house-flies, and in the larvae 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 (^Hippohoscce), the bird-flies {^Ornithomyi(B)^ 
the wingless sheep-ticks {Melophagi)^ and the spider-flies {Nycte- 
ribice\ and bee-lice {Braulm), 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 ( (Estrid<x)^ 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 larvae, 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 
