HYMENOPTERA 



885 



The membranous nature of the wings, which suggested the name 

 of the order, is not a distinctive characteristic, for it is possessed by 

 the wings of many other insects. 



The two pairs of wings are similar in texture. The wings of each 

 side are held together by a row of hooks, the hamuli, on the front mar- 



Fig. 1 1 26. — The veins of a typical hymenopterous wing. 



gin of the hind wing (Fig. 11 25); these hooks fasten to a fold in 

 the hind margin of the front wing, so that the two wings present a 

 continuous surface. The hind wings are smaller than the fore wings 

 and have a more reduced venation. Some forms are apterous. 



This is one of the orders in which in the specialization of the 

 wings the wing-venation is reduced. In the more generalized members 

 of the order this reduction of the wing-venation is slight, but in the 

 more specialized forms it is extreme. Even in the more generalized 

 forms, where nearly all of the veins are preserved, the courses of the 

 branches of the forked veins have been greatly modified. This has 

 been brought about by the coalescence of veins from the margin of 



Pig. 1 127. — The cells of a typical hymenopterous wing. 



the wing inward. To understand this one should study a series? of 

 wings of Diptera in which all stages of the modification of the venation 

 in this way are illustrated, for in the H}Tnenoptera only the later 

 stages are shown. The series of figures illustrating the coalescence 

 of veins Cu2 and 2d A in the Diptera will aid in understanding what 

 has happened in the Hymenoptera. 



Figures 1126 and 11 27 represent what may be regarded as a 



