402 



THE WINGS OF INSECTS 



the variations from this type are the result of either the coalescence of veins 

 or the atrophy of veins or of both of these processes. This fact is expressed 

 by the statement that in these orders the wings are specialized by reduction. 



In certain other orders of insects, of which the Neuroptera is one, the 

 wings that most closely resemble the hypothetical primitive type are those 

 that have few wing-veins compared with the wings of other members of the 

 order. In these orders the wings are specialized by addition. 



In those wings where the specialization has been by addition there are 

 usually many cross- veins; these, as a rule, are inconstant in number and 

 position, consequently, except in the case of a few of the more important 



Jf f rr ^7-7-77-7^77^. 



Fig. 418. — Wings of Polystoecholes punctatus. 



ones, which are not discussed in this brief introductory course, no effort is 

 made to name them. 



Accessory veins. — The added longitudinal veins are of two types, each 

 characteristic of different orders of insects. In the order Neuroptera, the 

 added longitudinal veins are of the type that has been designated as 

 accessory veins; they are \^eins that have been developed as branches of the 

 primitive longitudinal veins. 



The wings of Polysioechotes punctatus (Fig. 418) can be taken as an illus- 

 tration of wings that have been specialized by addition. In these wings 

 there are few cross-veins compared with what is usually the case in highly 

 specialized neuropterous wings; but these wings illustrate well a high 

 development of accessory veins. 



