608 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



ening the stigniatal region of the front wing, the second, the apex 

 of the first anal eell of the front wing, and the third, the stigmata! 

 region of the liind wing. The stigma, as already shown above, is the 

 cell Sc.,, in which the wing membrane is almost as strongly chitinized 

 as the veins surrounding it. In generalized genera it is a broad ovate 

 area, which undergoes a great reduction in the highly specialized 

 genera luitil it becomes a long, narrow cell, pointed at both ends. It is 

 located at the point where the greatest stress is exerted, and is in realit}' 

 a solid truss placed like a cap over this area subject to the greatest 

 stress. So that we have in the shape of the stignm a readily observed 

 criterion for judging the efficiency of the tiight of any species, and there- 

 fore the degree of specialization to which the species has attained. Now 

 if the stigmatal region of the front wing is examined, the following 

 conditions arc found. A large truss, truss 1, whose apex is near the 

 middle of the stigma, with one of its Ijasal angles at the base of the 

 wing, and the othei' at the apex of R,. Truss 2 has its apex near the 



2^^! 34 



:-^ r^ \ 





-THK I'KdNT \VIN(, ok BLENNOCAMl'A AND ITS TRUSSES. 



base of the stigma, with one of its basal angles at the point of separa- 

 tion of R and M, and the other in the angle formed by R^ and Mj. 

 Truss 3 has its apex near the middle of the stigma with one of its basal 

 angles in the angle between the medio- cubital cross-vein and cubitus, 

 and the other in the angle formed by R^ and Mj. Truss 4 has its apex 

 near the apex of the stigma with one of its basal angles at the point of 

 separation of R; and R«, and the other in the angle formed by the 

 radial cross-vein and ^,,+^. Truss 5 has its apex in the angle formed by 

 Ri and R„ with one of its basal angles in the angle formed by the medio- 

 cubital cross-vein and cubitus, and the other in the angle formed by R^ 

 and Mj. Truss 6 has its apex in the angle formed by R and M, with one 

 of its basal angles in the angle formed by the medio-cubital cross- vein 

 and cubitus, and the other in the angle formed by Mg+j and Mj+g. 

 Truss 7 has its apex at the point where the free part of R^ arises, with 

 one of its basal angles in the angle formed by Mg and M^, and the other 



