_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 ring 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_ _ff._ Slits of the posterior stigmata sinuous or bent. Subfamily Muscinæ. _g._ Slits of the posterior stigmata bent; usually two mouth hooks. _Muscina stabulans_ (fig. 171, l), _Muscina similis_, _Myiospila meditabunda_ (fig. 172, i), and some of the higher _Anthomyiidæ_. _gg._ Slits of the posterior stigmata sinuous; mouth hooks usually consolidated into one. The house-fly (_Musca domestica_ fig. 171, d), the stable fly (_Stomoxys calcitrans_), the horn fly (_Lyperosia irritans_), _Pyrellia_, _Pseudopyrellia_, _Morellia_, _Mesembrina_. _Polietes_, et. al. (fig. 172 in part).