aa. Body cylindrical, or slender conical tapering toward the head; without fleshy lateral processes ([fig. 105]).
b. With the posterior stigmata at the end of shorter or longer tubercles, or if not placed upon tubercles, then not in pit; usually without a "marginal button" and without a chitinous ring surrounding the three slits; the slits narrowly or broadly oval, not bent ([fig. 171 i]). Acalyptrate muscidæ and some species of Anthomyiidæ. To this group belong the cheese skipper (Piophila casei, figs. [98], [99]), the pomace-fly (Drosophila ampelophila), the apple maggot (Rhagoletis pomonella), the cherry fruit fly (Rhagoletis cingulata), the small dung fly (Sepsis violacea, [fig. 170]), the beet leaf-miner (Pegomyia vicina, [fig. 171 i]), the cabbage, bean and onion maggots (Phorbia spp.) et. al.
bb. Posterior stigmata of various forms, if the slits are narrowly oval ([fig. 171]) then they are surrounded by a chitin ring which may be open ventro-mesally.
c. Integument leathery and usually strongly spinulose; larvæ hypodermatic or endoparasitic. Bot flies ([fig. 171, f, g, k]).—Oestridæ
cc. Integument not leathery and (except in Protocalliphora) spinulæ restricted to transverse patches near the incisures of the segments.
d. The stigmal plates in a pit; the lip-like margin of the pit with a number of fleshy tubercles; chitin of the stigma not complete; open ventro-mesally, button absent ([fig. 171 e]). Flesh flies.—Sarcophaga
dd. Stigmata not in a pit.
e. The chitin ring open ventra-mesally; button absent ([fig. 171 c]). Screw-worm fly. Chrysomyia
ee. The chitin ring closed.
f. Slits of the posterior stigmata straight; marginal "button" present ([fig. 171 b]); two distinct mouth hooks, fleshy tubercles around the anal area. Phormia ([fig. 171 f]), Lucilia and Calliphora ([fig. 172, a, b]), Protocalliphora ([fig. 171, j]), Cynomyia ([fig. 171, a]). Blow flies, bluebottle flies. Calliphorinæ