1909] Homologies of Wiitg Veins 115. 



The tracheation of the wmg itself, however, is not sufficient 

 to define cubitus beyond cjuestion, and numerous mounts of 

 nymphal wing-pads were examined with this end in view. Per- 

 haps the most satisfactory is that. of Schizoneura rileyi (fig. 21) 

 in which a portion of the body trachea is seen with four main 

 wing tracheae, the fore-runners of radius, media, cubitus and the 

 first anal vein. 



Cubitus is here clearly shown in its relation to media and the 

 first anal and the peculiar complications of the venation of the 

 adult wing are thus explanable as coalescences with media on the 

 one hand or the first anal on the other. Schizoneura rileyi was 

 the only species in which the writer has succeeded in getting the 

 connection of these four nymphal wing tracheae with the body 

 trachea, but mounts of Callipterus ulmifolii showed four main 

 trachea? distinct to the base of the pad, as did also mounts of 

 Aphis sp. In the last nymphal stage there is a tendency, in 

 some species at least, for the basal portions of the medial, cubital 

 and first anal tracheae to become coalesced, giving the two main 

 tracheal stems of the mature wing. This is shown in a wing 

 pad of the last nymphal stage of Mindarus (fig. 18) where the 

 four main tracheae are distinct nearly to the base of the pad where 

 three of them become coalesced before reaching the body trachea. 



The vein cubitus so closely follow^s the cubital trachea that 

 a further discussion concerning it is not necessary. 



THE ANALS OF APHIDID^E. 



The same mounts which explain cubitus show just as clearly 

 the first anal and its relation to the other veins. We have then 

 the unmistakable homologies of four of the wing veins of Aphidi- 

 dse traced in the courses of the trachea of the freshly emerged 

 wings and the wing pads of the nymphs: the "first discoidal" 

 being the first anail, the "second discoidal" being the cubitus, 

 the "third discoidal" or "cubital vein" being the media and the 

 "fourth discoidal" or "stigmal vein" being the radial sector. 



This seems enough to ask of the tracheae of a highly specialized 

 wing, but they do tell even more. They give constantly the sec- 

 ond anal which appears in the freshly emerged wings for all the 

 genera studied by the writer, as a delicately marked and fairly 

 regularly placed trachea. No vein is formed about this trachea 

 so that it has no other significance for the venation than to help 

 determine that the anal vein here homologized as the first anal 



