107 



two causes results the transverse bracing of the radial area 

 of the wing, which is a very characteristic feature of the 

 venation of the wings in this order. 



The details of these changes will be made clear by an ex- 

 amination of Figures 8 and 9. The former represents the 

 primitive mode of branching of the radius ; the latter, the 

 radial area of the typical hymenopterous wing (Fig. 6). In 

 the hymenopterous type veins Jt z+3 and -/? 4+s of the primitive 



FIG. 8. The typical radius. 



FIG. 9. The radius in Hymenoptera. 



type coalesce so far that the branches of the sector arise 

 from a common stem ; and the tips of all of them have 

 moved away from the apex of the wing, veins ^? 2 and R^ 

 following the costal margin of the wing ; and veins R^ and 

 R^ following vein M r 



In the Hymenoptera the radial cross-vein is frequently 

 preserved; it is marked c v in figures 6 and 9. 



The student who has followed this discussion and has 

 understood it will be prepared to make original investiga- 

 tions of the venation of the wings of Hymenoptera. But no 



