THE FLIES THAT CAUSE MYIASIS IN MAN 43 



pattern, the design of which appears to change with the light incidence. 

 The arista is long-plumose above and below for more than half its 

 length, but not to the apex: the parafacials are hairy or bristly; the 

 vibrissae are well developed and close to the epistoma which is dis- 

 tinctly warped forward. The male lacks fronto-orbital bristles; the 

 female in most cases has three on each side, two proclinate and one 

 reclinate. There are three or more postsutural dorsocentrals, or, if 

 only two are evident, they are on the posterior half of the region 

 of the mesonotum behind the suture, the first two or more of the 

 series being absent. Vein m x bends abruptly forward so that the 

 first posterior cell is greatly narrowed but not closed ; vein cth. always 

 lacks setulae, although t\ and r 5 may be either setulose or bare. The 

 above characters are shared by most members of the genus (in the 

 broad sense) and will serve to separate it from most other genera. 



Specific determinations are difficult because of the large number 

 of similarly appearing species; they often depend on male genitalia 

 or secondary sexual characters of the male. Females therefore are 

 frequently undeterminable specifically. 



For a taxohomic treatment of the Xorth American forms of Sar- 

 cophaga. Aldrich (1) will serve, although some species have been de- 

 scribed since then and certain changes in names are necessary. Some 

 of these changes have been indicated in a later paper by Aldrich (2). 

 Rohdendorf (124) covers not only the Russian but to a large extent 

 the Palaearctic species ; the work is written in Russian, but the keys and 

 descriptions of new species, as well as of some other material, are 

 translated into German. Recently the species from other parts of the 

 world have been treated by Senior-White, Aubertin, and Smart (139 

 p. [208]-277) for the Oriental Region (not merely India, as are most 

 parts of this series). Hardy (52) for Australia, Lopes (84) for Hawaii, 

 Bezzi (IS) for the South Pacific islands, Patton and AVainwright 

 (110) for the British Isles, Curran (28a) for the Ethiopian Region (in 

 part). Hall (4-7) for Panama, Hall (4-8) for Patagonia and South 

 Chile, Curran (SO) for British Guiana, and Salem (128) for Egypt. 



Biology. — As far as known, the species are ovoviviparous, the fe- 

 males giving birth usually to a limited number of large and relatively 

 active larvae. Eggs are produced only under very unusual circum- 

 stances. Details of life histories vary considerably with different 

 species and in different localities for the same species, according to 

 published accounts, but the following statements seem to be typical. 

 The larva is forced from the larvipositor of the parent usually head- 

 first, and soon after emergence disappears into the food material. The 

 number of larvae produced by a gravid female ranges on an average 

 from 20 to 4<>. according to Knipling (73) ; some species will average 

 higher, however, and one gravid female of an unknown species gave 

 birth to 325 young. Development is rapid, the third instar usually 

 appearing in 3 or 4 days, and the adult emerging, in most species, in 

 about 2 weeks, although in some species the time required is much 

 greater. Hibernation in temperate climates is in the pupal stage. 



The fact that the larvae are produced alive and that their develop- 

 ment is very rapid should make one cautious in blaming contaminated 

 stools on cases of intestinal myiasis, since contamination can occur very 

 easily. It is possible for 1-day-old stools to contain third-stage larvae. 

 Knipling (73) records one case of a larva of SarcopTtaga stvmulans 

 Walker reaching the third stage in 21 hours, pupating in less than 



