574 



THE PANORPOID COMPLEX, 111., 



formed. In any case, the two-branched condition must be the 

 more specialised. .For, if M g had any part in the formation, 

 then the complete fusion, which brought about the two-branched 

 condition, is more specialised than the partial fusion, which left 

 the three-branched condition. But, if M s did not extend so 

 far distally, and dthe whole formation belongs to Cu, then the 

 natural explanation would be that the Mecoptera, Paratrichop- 

 tera and Diptera had lost the fork, which all the other Orders 

 have retained. 



Finally, it is necessary to add a word or two about the limits 

 of Cu in the Diptera. Text-fig. 48 shows the cubitus and por- 



M 



l-A- 



m.-ca- 



Text-Fig.48. 

 Structure of the media and cubitus in the forewing of a Dipteron, Rhy- 

 phus brevis Walk. (fam. Rhyphidae). The true medio-cubital 

 cross-vein, ni-cu, carries no macrotrichia. Lettering- as on p. 535. 

 (x 87.) 



tion of the media in the archaic Rhyplius, with the trichiation 

 in situ. It will be seen that the vein named by Comstoek Quj 

 (15, fig. 357) is really M 4) the basal portion connecting it with 

 Cu proper being a true cross-vein, without any lnacrotrichia, 

 while the short piece connecting it with M, which Comstoek 

 names the cross-vein m-cu, carries strong macrotrichia, and is 

 therefore the true basal portion of the main vein, M 4 . 



Further evidence on the same lines may be obtained by a 

 study of certain archaic Tipulid genera, such as the Australian 

 Gynoplistia, in which the original position of the branches of 



