The mouth parts are peculiar in that they are intermediate in form between the sucking beak of Hemiptera and the biting mouth parts of other insects.
Their eggs resemble those of Hemiptera; the larvæ and pupæ are active, and in form resemble the adult, except in the absence of wings. Some species, also, are wingless in the adult stage.
The pupæ are somewhat sluggish and the limbs and wings are enclosed in a thin membrane which is expanded about the feet into bulbous enlargements, giving rise to the name “bladder-footed” (Physopoda) applied to these insects by Burmeister.
Fig. 23.—A Mosquito (Culex pipiens).
a, adult; b, head of same enlarged; e, portion
of antenna of same; f, larva; g, pupa.
(After Westwood.)
“Order [DIPTERA] (δις, twice; πτερον, wing) or Two-winged Flies. The only order having but two wings, the hind pair replaced by a pair of small, slender filaments clubbed at tip, and called halteres, poisers, or balancers.
Fig. 24.—A Hawk-fly (Erax bastardi).
a, perfect insect; b, pupa; larva shown at side.
Fig. 25.—A Flesh-fly (Sarcophaga carnaria,
var. saracenæ). a, larva; b, puparium;
c, adult insect with enlarged parts.