the genitalia of Insects as guides in Phytogeny. 299 



through a immber of families in the Neiriatocera and the 

 Brachycera, and are in these cases useful Phylogeuetic 

 characters. It can be recognised in Scatopse, more par- 

 ticularly owing to the characteristic structure of the 

 ejaculatory sac. Pachyrrhina has only specific differences 

 from Tipvhi. In the Stratiomid Sarginse and Bering 

 great changes have taken place resulting m a shortening 

 and thickening of the style, and a simplification of the 

 ejaculatory apparatus ; but the type remains the same, a 

 chitinised process acting as a guide to a chitinised tube, 

 which expands into an ejaculatory apparatus. Quite close 

 to this are the forms of penis generally found in the 

 Asilida? and Dolichopodidse, while in some species of 

 Einpis they are very near Tvpukt in the flagellum, and 

 resemble the Stratiomyidye in the ejaculatory sac. The 

 Pipunculid Ghalitrusspurius, Fin., also has a styliform penis, 

 but differs in the ejaculatory sac which is membranous. 



The extraordinary contradictions in characters, struc- 

 tures which are usually only found in the older families 

 persisting side by side with late specialisations, show us 

 that reliance cannot be placed on any single character as 

 a test of Phylogeny. Whether that character be venation, 

 mouth part, genitalia, shape or microscopic structure, 

 unless supported by another character, it is apt to mislead. 



This is demonstrable by comparison of the mouth parts 

 of Glossina and Stomoitys ; both are, as is well known, 

 specialised for blood-sucking, and are somewhat alike in 

 appearance and arrangement of the parts. The impression 

 derived from a comparison of the male genitalia is very 

 different ; Stomoxys * is close to the normal Muscid type, 

 while in Glossina a remote and curious modification of 

 that type is established, which appears to be a generic 

 character, as I have found it common to the six species I 

 have examined. The venation also shows that while 

 Stomoxys approximates to the Cyrtoneurinoe, Glossina is 

 closer to the later Muscid type, as it is found in Calli- 

 phora, or as Mr. E. E. Austen points out to me, is nearly 

 identical with the OEstrid Hypoderhia. 



* The late F. Tullock, in his pa])er " On the internal anatomy 

 of Stomoxys," Proc. Roy. Sue, vol. 77 B, 1906, p. 525, describes the 

 penis as of the "same type as Glossina." In the sense that both 

 are Muscid in type, I am with him — but farther I cannot folhnv, 

 as the com])arison suggests to me an extremely remote degree of 

 relationshi]), or rather, a great divergence. 



