1909] Homologies of Wing Veins ^y 



the hind wing lacks the cubitus and is, therefore, a step in the 

 dn'ection of Chermes. 



Although we find the same veins in the hind wings of Macrosi- 

 phum solanifoln (fig. 8) and Pemphigus acerifolia (fig. 13) for 

 nistance, these two wings appear different on account of the 

 difference of position of the veins. The radial sector takes the 

 same course m both wings, but the free part of cubitus originates 

 much nearer the base of the wing in Macrosiphum while usually 

 m Pemphigus cubitus is coalesced with media to the point where 

 media branches off from the course of radius. This peculiarity 

 IS correlated with a similar manifestation in the front wincr of 

 Pemphigus and is doubtless due to the long narrow wino-s of this 

 genus. ^ 



In Chermes (figs. 30 and 3 1) as was stated in the discussion of 

 the tracheation, only veins radial sector and media are repre- 

 sented, and the hind wing of Phylloxera (fig. 32) has retained only 

 the radial sector. 



PSYLLIDyE. 



_ The tracheation of the psyllid wing is instructive both because 

 It throws light upon the interpretation of the venation of the 

 psylhd wmg and because it bears strong additional evidence in 

 support of the conclusions arrived at for the aphid wings. 



Fig. 3T> gives the tracheation of the fore-wing pad of'the nymph 

 of Psylla fioccosa Patch. It will be seen by reference to this that 

 there is no coalescence for these tracheae at this stage. They all 

 branch separately from the body trachea. There are seven\ra- 

 chese : the costal : a short trachea lying at the verv margin of the 

 wmg pad; the unbranched subcostal extending in a line about 

 parallel to the costal margin of the pad and lying very close to 

 the costal trachea at the base; the radial, terminating in two lon^ 

 branches, the forerunners of R, and Rs; the two-branched medial" 

 the typical two-branched cubital; and two anal tracheae 



This comes surprisingly close, for a wing so highly specialized 

 to the hypothetical type of Comstock-Needham. 



The newly emerged wing shows a decided change in the appear- 

 ance of the tracheae, but the change is due to basal coalescence 

 instead of any radical change in the number or branching of the 

 trachea. 



The tradieation of the freshly emerged wing of Psylla fioccosa 

 {tig.i, 4} shows the degree of this change. The costal trachea has 



