1909] Homologies of Wing Veins 105 



the best results were obtained. However, none of the aphids 

 are so easy to manipulate for the tracheation of the wing pads as 

 are the fiat padded psyllids. 



* »!» »t* %s^ %^ 



^^ ^t* ^* *!* 



Although the possibilities of interesting features of wing tra- 

 cheation of the aphids were by no means exhausted with any 

 species; for the problem at issue, — the homologies of the wing 

 veins, — -no point was left in question. Wings of more than two 

 thousand of newly emerged aphids were examined. Where 

 possible a single point was verified for all the variations of wing 

 types from Lachnns to Chermes. Where a point arose that cer- 

 tain species showed better than others it was exhaustively studied 

 by making numerous mounts of those species which had any bear- 

 ing upon it. 



As for the range of material used, approximately 100 species 

 belonging to 16 genera were drawn upon. Many of these were 

 discarded after a few mounts, — as for instance after the condition 

 for the genus Aphis was clearly ascertained other species of this 

 genus did not give additional data. Many species were found 

 unsatisfactory to work with by reason of size, density of color 

 or other conditions and were discarded after a few trials. 



The genera from which most of the data were accumulated 

 and in all of which the tracheation was demonstrated repeatedly 

 and conclusively, are Lachnus, Melanoxanthus, Callipterus, Chai- 

 tophorus, Myzus, Macrosiphum, Rhopalosiphum, Aphis, Schizo- 

 neura, Mindarus, Pemphigus, Tetraneura, Hamamelistes, Cher- 

 mes and two new genera still in manuscript. These genera pre- 

 sent practically the w^hole variation of the types of aphid venation 

 from the more generalized to the more specialized. 



The more logical presentation of the four families considered 

 in this paper would be in the following order, — Psyllidee, Aphididae, 

 Aleurodidas and Coccidce, but as the problem was undertaken 

 primarily for the Aphididae and as the investigation was devoted 

 for the most part to them, the part dealing with the aphids is 

 presented first. The work with the other families, though suffi- 

 cient to indicate the homologies of the veins, has been so much 

 slighter in amount that it seems more fitting to give secondary 

 place to the Psyllidse even though this necessitates a break in the 

 systematic sequence. 



