CHAPTER VII. 



THE VENATION OF THE WINGS OF INSECTS. 



In form an insect's wing is a large, membranous append- 

 age, which is thickened along certain lines. These thick- 

 ened lines are termed the veins or nerves of the wing ; and 

 their arrangement is described as the venation or neuration 

 of the wings. 



It has been found that the venation of the wings of closely 

 allied insects is very similar, and that great differences in 

 this respect exist between insects remotely connected. Hence, 

 the wings afford excellent characters for use in the classifica- 

 tion of insects. In fact, as slight differences in venation are 

 easily observed, the wings being spread out like an open 

 page, these differences are probably the most available charac- 

 teristics of insects for taxonomic work. It is important, 

 therefore, that the student of entomology should learn earl} 7 

 in his course the more important facts regarding this subject. 



A careful study of the wings of many insects has shown 

 that the fundamental type of venation is the same in all of 

 the orders of winged insects. But this fact is evident only 

 when the more primitive or generalized members of different 

 orders are compared with each other. In most of the orders 

 of insects the greater number of species have become so 

 modified or specialized as regards the structure of their wings 

 that it is difficult at first to trace out the primitive type. 



The specimens indicated for the student to study in the 

 following part of this course have been selected with care to 

 illustrate gradually increasing degrees of divergence from 

 the primitive type. In the case of each order studied the 

 work begins with a comparatively generalized form, and 

 passes step by step to those that are more specialized. 



