406 



THE WISGS OF INSECTS 



of the Neuroptera are de\^eloped- In the Ephemerida the added longitudinal 

 veins are de\'eloped in each case as a thickened line more or less nearly 

 midway between two preexisting veins; for this reason they are termed 

 intercalary veins. 



Fig. 422. — A fore wing of a May-fly. The convex veins are marked 

 + ; the concave veins — . 



When it is desirable to refer to a particular intercalary vein it is done 

 by connbining the initial I, indicating intercalary, with the designation of 

 the area of the wing in which the intercalary vein occurs. For example, 

 in the wings of most May-flies in which the venation is not reduced, there 

 is an intercalar\' vein between veins Cui and Cu2, i. e. in the area Cui. This 

 intercalary vein is designated as ICui. This and other intercalary veins 

 are represented in Figure 422. 



IDENTIFICATION OF THE WIXG-VEIXS AND OF THE CELLS OF THE WINGS IN 



HYMENOPTERA 



The determination of the homologies of the wing-veins of Hymenoptera 

 is very difficult, as even in the most generalized of the living members of the 

 order the venation of the wings departs widely from the primitive type. 



In the Hymenoptera, as in the Diptera and in the Lepidoptera, the 

 specialization of the wings is by a reduction in the ntmiber of the wing- 

 veins, the more generalized forms possessing the maximum nimiber of wing- 

 veins found in the order. In the more generalized families the reduction of 

 the wing-venation is slight; in the more specialized families, it is extreme. 



The most characteristic method of modification of the wings of Hymen- 

 optera is by the coalescence of veins from the margin of the wing towards the 

 base of the wing. This results frequently in a branch of a longitudinal 

 vein becoming transverse, so that it appears like a cross-vein ; and in some 

 cases, where the coalescence has been carried still farther, a branch of a 

 longitudinal vein has been so diverted from its primitive course that it 



