9'^g] Homologies of Wing Veins 



121 



a terminology which has the same significance for not only the 

 closely related families of Aphididce, Aleurodidas, and Coccidae, 

 but the other insect orders as well. 



For instance it would certainly seem more convenient to say 

 "M + Cu is longer than the stem of R" than to resort to the more 

 tortuous statement of Maskell*: "the stalk of the lower branch 

 (cubitus) of the furcation of the primary vein is longer than the 

 stalk of the upper branch (subcosta)." 



At present the veins in the figures of the psyllid wings are 

 indicated by arbitrary letters or figures with no necessary relation 

 to symbols used by the same author for any other psyllid wing 

 or to those of any other author for the same wing. This hap- 

 hazard arrangement of lettering or numbering the figures of 

 psyllid wings increases the confusion caused by the fact that 

 the veins themselves are cumbered with such a system of nomen- 

 clature as the following: 



"Stalk of cubitus, lower branch of cubitus, lower fork of lower 

 branch of cubitus, upper fork of lower branch of cubitus," etc. 



But by the use of a uniform system of wing terminology the 

 abbreviation of the names of the veins become the natural and 

 inevitable symbols to use for lettering the figures of the wings, 

 and no confusion arises in associating Rs of the figure, for instance, 

 with the radial-sector of the text. 



The relative simplicity, ease of abbreviation and uniformity 

 of such a system of terminology is recommendation enough aside 

 from the homological significance it bears. f 



As is stated in the discussion of Redtenbacher's homologies 

 (see page 125) except for his interpretation of the alternate con- 

 cave and convex veins his terms for the psyllid veins are in the 

 main those applied in this present paper upon the basis of the 

 tracheation. 



ALEURODID^. 



Four fine but distinct trachea are present in the freshly 

 emerged wing of Aleurodes 5^.,— the costal, subcostal, radial and 

 cubital tracheae (fig. 44). All of these are uncoalesced to the 



* Maskell: Trans of the N. Z. Institute, Vol. XXII, 1899, page 158. 



t The Comstock-Needham system of terminology has been adopted by 

 Handlirsch in all his recent papers dealing with venation of fossil insects and in 

 his extended monograph of the fossil insects of the world. (Die F"o.ssillen Insek- 

 ten und die Phylogenie der Rezenten Formcn 1906-1908). It has been with 

 interest that the writer has noticed the application of this system of nomenclature 

 to the group of insects with which this present paper deals, especially as the basis 

 for his conclusion was a study of the treacheation of the wings. 



