168 FOREST ENTOMOLOGY. 



on this account and partly because they divide the wing into areas 

 named from them, and from these areas again are named most of 

 the (transverse) 'nerves' and the 'cells' or divisions of the areas 

 bounded by them. 



" Starting from near each other, and near the base of the wing, five 

 main ' veins ' run, all more or less in the direction of its apex, but 

 radiating apart, like the fingers of an extended hand. 



" The first pair start at a and b : these are the costa and the sub- 

 costa. The costa follows the actual margin of the wing, and the 

 sub-costa runs nearly parallel to it for about half the length of the 

 wing, when it bends upwards and unites with the costa at /, just 

 before the stigma (the shaded area in fig. 159). 



"From d and e start another pair, the brachius and the humerus. 



Fig. 159. Typical tipper wing of saw-fly. (Sketch by Rev. F. D. Morice. From 

 'Entomologist's Monthly Magazine.') 



These run both somewhat parallel to the lower margin of the wing, 

 but neither of them coinciding with it. Again, for about half the 

 total length of the wing, the humerus turns upward and joins the 

 brachius at g (just as at / the sub-costa joins the costa). The 

 brachius is continued a little farther to x, and there disappears. 



"The fifth of these 'veins,' starting at c, is called the medius. It 

 runs at first straight along the middle of the wing (equidistant, there- 

 fore, between the two pairs described above) for half its length. Then 

 it bends downwards as though to join the brachius, but at t turns 

 suddenly off, resuming its horizontal course, then (at u) is again 

 deflected, and reaches the margin at v. 



" Besides the above five main veins, we have two which may be 

 called subsidiary. They are confined to the superior (apical) quarter 



