ANATOMY AND PHYSIOLOGY 



47 



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

 branched, as in Fig. 67. 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. 



E! R2 



R3 



FIG. 68. Wing of a fly, Rhyphus. Lettering as before. 



The anal veins (A) are typically three, of which the first is generally 

 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 primi- 

 tive type of venation; which is well preserved, also, in the more general- 

 ized 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 NS^X^ \^ ^\ ^m M2 



of all but one anal vein in 

 Rhyphus (Fig. 68) and other 

 Diptera, and the absence of 

 the base of the media in 

 Anosia (Fig. 69) 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 coales- 



2dA 



FIG. 69. Wing of a butterfly, Anosia. Lettering as 

 before. 



