THE HYMENOPTERA. 221 



Like the Neuroptera^ the insects of this order have 

 four membranous wings, but these are of a very 

 different construction. The posterior pair are always 

 much smaller than the anterior, with which they are 

 held in connexion during flight by a series of minute 

 hooks along a portion of their anterior margin, which 

 catch the hindmost vein of the anterior wing as the 

 latter slides over them in extension. During repose, 

 the wings are laid over eacli other upon the back of 

 the insect. 



The veins by which the membrane of the wings is 

 traversed are few in number when compared with 

 those exhibited by most of the Neuroptera; but to 

 make up for this comparative paucity, they are usually 

 arranged in such a manner as to produce several cells 

 of a very regular figure on the surface of the wing, 

 and the number and arrangement of these and of the 

 veins in general furnish some of the most important 

 characters for the determination of genera. Never- 

 theless, at the first glance, it might be supposed that 

 there was but little difference in the neuration of the 

 wings of the majority of the Hymenoptera ; and it is 

 only when we come to compare them carefully with 

 one another, that we recognize certain apparently 

 slight but characteristic peculiarities in the species 

 of nearly allied genera, which, however, are usually 

 so constant that the Hymenopterist can depend upon 

 them as distinguishing marks. It is to be observed, 

 however, that in some species, and even groups, the 

 number of veins is greatly reduced, and sometimes 

 the wings are almost destitute of them, whilst these 

 organs are wholly wanting in other cases. 



The head is usually rather large and broad, but is 

 always attached to the thorax by a distinct narrow 



