pupae of the ancestors of such species lived in the same medium as the larvae.. Ifour supposition is correct, we may see a reason tor the apparent exception in the files to the general rule that the pupa presents the adult structure and discards the pecu- liarly larval characters. The pupae of some flies whose
Fro. ?73- Larva (A) and pupa (B) ofa horsefly, Tabanus puncti- fer (about 1 ? rimes natural size) ?/n, anus; H, head; PSp, posterior spiracle; Sp, spiracle larvae lire in the water, however, revert at once to the adult system of lateral spiracles (Fig. ?73 B, Sp). With such species, the larva comes out of the water just before pupauon time and transforms in some place where breathing is possible by the ordinary respiratory organs. This is the general fuie with other insects whose larvae are aquatic. The order of the Diptera is a large one, and we might go on indefinitely describing interesting things about flies m general. Such a course, however, would soon fill a larger book than this; hence, since we are already in the last chapter, a more practical plan will be to select for special consideration a few species that have become closely as- sociated with the welfare of man or of his domesticated animais. Such species include the mosquitoes, the bouse fly, the blowfly, the stable fly, the tsetse fly, the flesh files, and related forms.
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