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 (I/) is often three-branched and is typically four-branched, 

 according to Comstock and Needham. 



The cubitus (Cu) has two branches. 



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 

 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. 



