146 



THE WINGS OF NEUROPTERA 



(b) THE SPECIAL FEATURES OF THE WJNGS OF THE NEUROPTERA 



In the order Neuroptera there are several very distinct types of speciali- 

 zation of the wings. Some of these are described in the accounts of the 

 wings of the families in which they occur; but there are others that are 

 characteristic of more than one family ; these are described here in order to 

 avoid repetition. 



The accessory veins. — In some Neuroptera the development of acces- 

 sory veins has progressed to a very limited extent ; but in a much larger 



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Fig. 137. — Wings of Osmylus hyalinalus. 



number of representatives of this order the most striking features of the 

 wings are produced by accessory veins. It is here that the development of 

 accessory veins, both definitive and marginal, reaches its most perfect 

 condition, and wings of wonderful beauty of form are the result. 



The definitive accessory veins of the Neuroptera are produced in two 

 ways ; in some cases they are added distally by successive splittings of the 

 tip of a principal vein, thus forming a regular series; in other cases, the 

 number of accessory veins is increased in an irregular manner, by the split- 

 ting of branches of the principal veins. Wings illustrating each of these 

 methods of increase in the number of accessory veins are figured later. 



