THE CANADIAN ENTOMOLOGIST 51 



some of these characters become highly untrustworthy, though 

 they may hold good throughout other groups. It is often quite 

 impossible to decide their values correctly without the aid of 

 the reproductive and early-stage characters to guide us in the 

 matter of close relationships. An intricately interrelated system 

 of specialization in external adult anatomy has resulted in pro- 

 ducing in distinct stock forms which closely approach each other 

 in external characters. This was not realized until the investi- 

 gation of the reproductive and early-stage characters had con- 

 siderably progressed. 



Until this work was well under way no one could interpret the 

 genera as they actually exist, and all generic work was largely 

 guess-work. Even at the present time muscoid genera as they 

 commonly appear in the literature are in numerous cases 

 complexes of widely different stocks. Forms belonging to 

 distinct families have for a century been classed as 

 congeneric, and the external differences between them are some- 

 times so inconspicuous that careless workers have even pronounced 

 them conspecific. These facts serve to emphasize the invaluable 

 aid to be derived from the reproductive and early-stage characters, 

 and the necessity for taxonomic manipulation of the superfamily 

 by means of smaller groups than families, subfamilies, tribes, 

 and subtribes. 



The following tabular summary will be useful. It shows 

 the known main differentiations of the female reproductive system, 

 eggs and first-stage maggots in /the eleven muscoid families here 

 recognized, exemplified by group-units. The group-unit consists, 

 as already stated, of the typic genus plus the atypic genera which 

 belong with it, and is a. division of the subtribe. 



Its ending is i(2, which is added to the root of the name of 

 its typic genus. 



1. Elongate macrotype eggs deposited 

 subcutaneously without incuba- 

 tion, no uterus — Phasiiae. 



2. Flattened subovate macrotype eggs 

 deposited supracutaneously with- 

 out incubation, no uterus — Ecto- 



^^ phasiia?, Trichopodiae, Xanthome- 



I. PHASIID.E 



