114 Amials Entomological Society of America [Vol.11, 



mal portions of cubitus and the first anal vein. The free part of 

 media occupies about the center of the distal half of the wing. 

 Its maximum number of branches is three, — Mj and M, and 

 M3 + 4 (fig. 8). The first step at reduction is in such wings as 

 Schizoneura and Mindanis where Mi and M, are coalesced, giving 

 a two-branched media Mj + j and M3 + 4 (figs. 20 and 23). These 

 two branches in turn are coalesced, resulting in the unbranched 

 media (M1 + 2 + M3 + 4)* in the wings having the most reduced 

 venation. 



The connection between the free parts of media, cubitus and 

 the anal vein and the composite main vein is frequently broken, 

 on account, probably, of the strong ridge in the wing caused by 

 this vein. This part of media being in the central portion of the 

 wing is not, apparently, so necessary to the strength of the wing 

 as the veins on either side, and starting from the broken basal 

 connection media is found in various degrees of atrophy, in some 

 species one-third to one-half of the base of the free part of media 

 being lacking (fig. 17). 



CUBITUS OF APHIDID^. 



Cubitus is present in all the genera of Aphididas and in all of 

 them unbranched. 



The tracheation of the freshly emerged wing and of the wing 

 pad explains cubitus and its relation to the other veins. 



x\ttention is called to figure 2 2 , Schizoneura rileyi, which gives 

 a fair illustration of the cubital trachea. Its basal portion is co- 

 alesced with those of the medial and anal tracheae. In most 

 wings the free portion of the cubital trachea originates about mid- 

 way between the medial and first anal tracheae. In some instances 

 however, the cubital trachea runs along parallel with the medial 

 trachea for some little distance. Figure 9, a mount of a newly 

 emerged hind wing of Macrosiphum pisi, is an unusual instance 

 even for the species in question, where the cubital trachea runs 

 parallel with the medial to almost the base of the wing before it 

 becomes coalesced. On the other hand, in the wing of Hamame- 

 listes spinosus (fig. 15) a greater degree of coalescence has taken 

 place and the cubital and first anal tracheae branch from the me- 

 dial on a common stem, and proceed ^ome little distance before 

 separating. 



* See page 106 for a discussion of the course of a vein. 



