68 



THE GENERAL FEATURES OF WINGS 



indicate this fact. In the wing of Rhyphiis (Fig. 52), for example, radius 

 is only three-branched; but it would be misleading to designate these 

 branches as Ri, R2, R3, for this would indicate that R4 and R5 are lacking. 



/?, ^.+3 



id A 

 Fig. 52. — Wing of Rhyphus. 



The first branch is evidently Rr, the second branch is composed of the 

 coalesced Ro and R3, it is, therefore, designated as R2+3; and the third 

 branch, which consists of the coalesced R4 and R5 is designated R4+5- 



The wing of Rhyphus illustrates also the other method of reduction of 

 wing- veins, as the basal part of media has faded otit. 



A second method of coalescence of veins is illustrated by the wing of 

 Tahanus (Fig. 53). In this wing the tips of cubitus-two and the second 

 anal vein are united; here the coalescence began at the margin of the wing 

 and is progressing towards the base. The united portions of the two veins 

 are designated as 2d A + Cu2. 



In those cases where the reduction of the venation has proceeded very 

 far, as in some of the smaller Hymenoptera for example, the logical carrying 



2d A^'^Cu, 

 FiS- 53- — Wing of Tahanus. 



out of the plan of designating a compound vein by a combination of the 

 names of all of the veins that have entered into the composition of it would 

 result in a very cumbersome terminology. Such a designation, however 



