50 THE CANADIAN ENTOMOLOGIST 



ready outlined may stand forth on. general characters, it is never- 

 theless true that the recognition of the family groups which the\" 

 typify does not facilitate synoptic treatment. Their employment 

 does not elucidate the subject, but rather obscures it. They are 

 often incapable of concise limitation and hence of compact synop- 

 tic definition on either external, reproductive or early-stage charac- 

 ters. Thus it is necessary to sidetrack them in actual synoptic 

 practice and drop to lower categories. The group-unit is the 

 category that here lends itself most conveniently to taxonomic 

 manipulation. The reason for this lies in the fact that the charac- 

 ters of the reproductive system, egg and early stages, which can 

 not always be conveniently interpreted as of family value, and 

 often of subfamily or even of subtribal value, are much more 

 pronounced and readily apparent, therefore more comprehensi^'e, 

 than those characters of the external anatomy of the fly which 

 largely mark convenient family to subtribal divisions. While the 

 characters of the facial plate and various supporting characters 

 of family to subtribal importance exhibited by other external 

 adult structures are often by themselves almost impossible of 

 correct interpretation, so much so that hardly any two persons 

 can be expected to read them alike, those of the reproductive 

 system, egg and early stages are unmistakable and impossible of 

 confusion. 



Such external adult characters as the more or less ciliate 

 facialia, degree of hairiness of eyes, apical cell ending at or near 

 wing-tip, presence of true macrochaetae, hind tibia? ciliate or 

 pectinate, relative length of aristal and antennal joints, relative 

 development of antennae, mouth-parts and palpi, and especially 

 exact plan of facial plate specialization including degree of con- 

 striction by vibrissal angles and their comparative degree of 

 removal from the oral margin with the conformation of latter. 

 in fact the majority of the external adult characters in these flies. 

 are very difficult to describe accurately and few persons will be 

 able correctly to interpret the descriptions in any event. More- 

 over these characters indicate close relationships only in certain 

 cases, while in others they are the result of evolutional trend in 

 stocks considerably removed from each other. For this and 

 other reasons their value runs out at times. In certain groups 



