6o 



ENTOMOLOGY 



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 complete. Coalescence " takes place in two ways : 

 first, the point at which two veins separate occurs nearer and 



/ A 



Wing of a fly, Rhyphus. Lettering as before. 



nearer the margin o,f 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 



R3 



Cu2 



2dA 



Wing of a butterfly, Anosia. Lettering as before. 



proceeds towards the base of the wing." (Comstock and Need- 

 ham.) The former, or outward, kind of coalescence is com- 

 mon in most orders of insects; the latter, or inward, kind is 

 especially prevalent in Diptera. 



Specialization by addition occurs by a multiplication of the 

 branches of the principal veins. 



