b 



the genitalia of Insects as guides in Phijlogeny. 301 



seems to foreshadow the Muscid type, in the syniuietry and 

 regularity of the lateral processes, while the forms found 

 in CvJcx and Gynoplista do not seem to bo represented in 

 later families. 



The Tabanidse and Leptida3 are closely allied on the 

 venation, but far apart on the characters of the mouth 

 parts, the details of structure being without suggestion 

 of affinity, the mandibles having disappeared, and a much 

 simjaler armature being usually found in the latter family. 

 The genitalia in T. Iromim, L., ^, are very complicated in 

 the details of the ejaculatory apparatus, yet these com- 

 plications are closely reproduced in Lcptis consjucmc, Mg,, 

 and with less difference than is often found between the 

 species of the same genus. 



Another point that suggests affinity is similarity of 

 arrangement. In a number of families in Diptera, the 

 hypopygium is turned in under the abdomen ; but in only 

 one, the Dolichopodida^, and that only in certain genera, 

 are the appendages that surround the penis displayed 

 and disposed outside the cavity. An examination of the 

 armature in the Phoridifi shows a prominent hypopygium, 

 but the microscope shows that it consists of two portions, 

 a segment supporting the anus and the representatives of 

 the larger hooks (Dr. J. H. Wood's " anal protuberance "), 

 and a second segment often with aculeations, containing 

 the penis. This second segment, judging from numerous 

 points of comparative anatomy, homologises with the 

 appendages that surround the penis (theca), which are, as 

 in Dolicliopiis, displayed outside the hypopygium. 



This similarity of arrangement exists without the least 

 trace of similarity of detail (unless it be in Conicera) or of 

 structure suggesting affinity ; but as there are striking 

 points in the antennae, the mouth and general structure 

 that show an affinity between the Phorida) and the 

 Dolichopodida^, the similarity of arrangement appears, 

 especially as it is so singular, to be of Phylogenetic value.* 

 A remarkable development of the genitalia, both in the 

 male and the female, in some of the Acalyptrate MuscidjB 

 has been undervalued by systematists. It is true that in 

 Osteu-Sacken's list of 1878 and Verrall's British list of 



* In soino rare cases asymmetrical forms of the inner parts are 

 found, as in Fcripldnpta, and I have also foiuid such a state in tlie 

 "second" segment (the corresponding part) and its contents in some 

 Phorida?. 



