1909] * Homologies of Wing Veins 113 



lies uniformly parallel to the radial trachea, usually separated 

 from it by an appreciable distance, though often touching it, but 

 not, except in rare instances,* really coalesced with the radial 

 trachea. As we approach the wings most specialized by reduc- 

 tion of tracheae, we come first to Schizoneura (fig. 22) and Min- 

 dariis (fig. 19) as examples of the medial trachea with but two 

 branches, and then to such wings as those of Pemphigus, Tetra- 

 neura, Hamamelistes and Chermes, where media is unbranched. 

 The migration of the medial trachea to approximately the position 

 occupied by the radial sector which in turn migrates to meet the 

 margin of the stigma, is characteristic of the Chermesinse, and has 

 just been discussed under the treatment of radius. 



The tracheation of the adult wing, however, does not suffice 

 to make perfectly evident the relation of media to cubitus. For 

 instance, so far as has yet been demonstrated, what is here inter- 

 preted as M3 + 4 (fig. 22) might perhaps be understood as cubitus 

 coalesced with media as Vickeryf has explained it, or what is 

 here interpreted as cubitus might be homologized as a branch of 

 media as Handlirsch| has done. Fortunately the tracheation of 

 the wing pad of the nymphs of certain species make this point 

 entirely clear. Reference to the nymphal pad of Schizoneura 

 rileyi (fig. 21) gives an unmistakale demonstration concerning the 

 point at issue. Four main tracheae are seen to be separate to the 

 place of connection with the body trachea. These are the fore- 

 runners of radius, media, cubitus and the first anal vein. The 

 two-branched media and the unbranched cubitus of Schizoneura 

 are thus clearly seen to be preceded by distinct tracheae separate 

 to the base of the wing pad, and the relation of media to cubitus 

 in the mature wing becomes at once apparent and the degree of 

 basal coalescence evident. 



After the foregoing discussion of the tracheation little remains 

 which needs to be said concerning the vein media. For approxi- 

 mately one-half the length of radius media is coalesced with 

 R-1-Sc.|| and nearer the base of the wing similarly with the proxi- 



* For discussion of coalescence and anastomosis of the tracheae, see page 106. 



t Vickery, '08, page 9. Figure 2. 



i Handlirsch. Die Fossilen Insekten und die Phylogenie der Rezentcn For- 

 men. 1906-08. Taf. VIII, figures 9 and 10. 



II "The figures show that in some cases what appears as a single vein is 

 formed about two closely parallel tracheas. This is shown in the case of the 

 bases of the second and third principal tracheae, counting from the costal margin 

 of the wing, the radial and medial tracheae. This illustrates a fact of frequent 

 occurrence, that what appears to be a single vein may be formed by the coales- 

 cence of two primitive veins." Comstock-Needham, Wings of ln.sects, p. 48. 



