91 



There are still other writers who do not regard the costa as a true vein, 

 and, therefore, designate the subcosta as vein I. 



The result is that there are three distinct systems of numbering the wing- 

 veins, in addition to several old systems which were applied to single orders. 

 It seems better, therefore, to designate the wing-veins by names, and use 

 abbreviations of these names in lettering figures. 



Names of the cross-veins. — In the Diptera and in cer- 

 tain other orders of insects there are so few cross-veins that 

 it is practicable to apply names to them ; these are as follows : 



The humeral cross-vein. — This is a single cross-vein ex- 

 tending from the subcosta to the costa near the base of the 



C 



Fig. 3. — Fore wing of a butterfly with the veins and cells numbered. 



wing. This is the most constant of all of the cross-veins. 

 It is represented in Figure 2, but is not lettered. 



The radial cross-veiti. — This is a cross-vein which divides 

 cell R^. (The cells are defined a little later.) The radial 

 cross-vein is not represented in Figure 2. 



The radio-medial cross-veiti. — This is a cross-vein extending 

 fpom the radius to the media, usually near the center of the 

 wing, and is designated by the abbreviation r-fn. When in 

 its typical position this cross-vein extends from vein R^^^ to 

 vein J/,+j ; this results in one end being opposite cell R^ and 

 the other end opposite cell ist M,^. 



