30 BEES AND WASPS [OH. 



two-thirds of its length from the attachment to the 

 body. From the stigma there starts a nervure which 

 at first sweeps backwards (in the outstretched wing) 

 and then forward again and outward up to the front 

 margin so as to enclose an area termed the marginal 

 cell. The two other horizontal nervures, taken in 

 order, are respectively the median and the posterior. 

 In order to explain the peculiarity of the forewing 

 of a Crabro we must crave the indulgence of the 

 reader a little further, and mention a few of the 

 nervures which run across the wing in a more or less 

 transverse direction the remainder of these shown 

 for the sake of completeness in fig. 4 need not here 

 concern us. The first of these transverse nervures, 

 starting from the body, occurs at about a third of 

 the length of the wing and extends from the post- 

 costal across the median to the posterior nervure : it 

 is known as the basal nervure, and is not straight but 

 more or less zigzag with distinct angles along its 

 course. It will be seen that this basal nervure marks 

 out two "cells"; one, the upper basal cell, between 

 the post-costal and median nervures; the other, the 

 lower basal cell, between the median and the pos- 

 terior nervures. The basal nervure thus forms the 

 outer boundary of both these cells. From about 

 the middle of both the upper and the lower part 

 of the basal nervure, i.e. from about the centre of 

 the outer boundary of both the upper and lower 



