^98 Mr. W. Wesche's Notes on the value of 



most conservative in form), the male genitalia follow 

 closely a common type. 



Further, comparing family with family, one realises 

 that cases of parallel development or degeneration occur. 

 Many instances are found in the tropin ; the mouth parts 

 in Conops, certain Cyrtidai, Proscna and Glossina are much 

 alike in appearance, and the proboscis is formed in all 

 cases from a modification of the under plate (mentum), 

 and only differs in detail, yet this similarity is clearly no 

 indication of affinity. 



In the genitalia, the ovipositor may be especially modi- 

 fied and hardened into a boring apparatus as in the 

 Phytomyzidse, but a somewhat similar chitinising of the 

 extremity in the viviparous Phora rnficoTnis, Mg., is no 

 sign of relationship. 



The degeneration of the wings is another similar 

 character, and I think we must admit a tendency in the 

 smaller forms in families, towards a simplification of the 

 venation, and this must go into the same category. It 

 is obvious that these parallel developments or degenera- 

 tions must be recognised and ignored, when taking into 

 consideration any Phylogenetic characters. 



The lines of modification in the male genitalia all tend 

 to two ends, an effective fertilisation of the female and an 

 effective isolation of the species; so that these may come 

 under the head of parallel developments, but as the second 

 cause must result in very varied morphology, it can be 

 excepted from the above generalisation. Indeed in these 

 variations in the inner parts (the penis and its append- 

 ages) are to be fouml the more valuable Pliylogenetic 

 characters ; the outer claspers (the forcipes superiores and 

 iuferiores of Dziedzicki) are sometimes of generic, but 

 oftener only of specific value, as may be seen in Anopheles 

 and Tanypus. 



In families which may be considered some of the oldest 

 in the Nematocera, three types of penis are found : (1) a 

 long styhform tube as in Tipula ; (2) a prominent chitinous 

 process with lateral processes, as in FtAjclioptcra ; (3) and 

 a low membranous process supported by lateral chitinous 

 hooks or levers, as in the Australian genus Gynoplistia 

 and in Culex. 



Of these three forms the most striking is that of 

 2\'pula, and I think it can be clearly shown by methods 

 of comparative anatomy, that modifications can be traced 



