

ANATOMY AND PHYSIOLOGY 



55 



The radius (R), though subject to much modification, is typically 

 five-branched, as in Fig. 69. The second principal branch of the 

 radius is termed the radial sector (Rs). 



The media (M) is often three-branched and is typically four- 

 branched, according to Comstock and Needham. 



The cubitus (Cu) has two branches. 



Rl R2 



Cu> 

 FIG. 70. Wing of a fly, Rhyphus. Lettering as before. 



The anal veins (^4) are typically three, of which the first is usually 

 simple, while the second and third are many-branched in wings that 

 have an expanded anal area. 



The Plecoptera, as a whole, show the least departure from the 

 primitive type of venation; which is well preserved, also, in the more 

 generalized genera of the Trichoptera. 



Starting from the primitive type, specialization has occurred in two 

 ways: by reduction and by 

 addition. Reduction occurs 

 either by the atrophy of veins 

 or by the coalescence of two 

 or more adjacent veins. 

 Atrophy explains the lack of 

 all but one anal vein in 

 Rhyphus (Fig. 70) and other 

 Diptera, and the absence of 



the base Of the media in A no- FlG - 7 1 Wing of a butterfly, Anosia. Lettering 



as before. 



sia (Fig. 71) and many other 



Lepidoptera; in the pupa of Anosia, the media may be found com- 

 plete. Coalescence " takes places in two ways: first, the point at 

 which two veins separate occurs nearer and nearer the margin of the 

 wing, until finally, when the margin is reached, a single vein remains 

 where there were two before; second, the tips of two veins may approach 

 each other on the margin of the wing until they unite, and then the 

 coalescence proceeds towards the base of the wing." (Comstock and 



