The two-winged flies are more important in nature than any other order of insects because of their number and diffusion, and the families may be briefly traced in succession previous to a more extended notice of each of them, in case the subject should become rnore interesting.

In the following arrangement the first manifestation of Dipterous. existence is associated with the inmost recesses of man's habitation. and a few beasts and birds aiso partake of its presence in their dwellings.