Comparison of Normal and Brachypterous Wings.

Forewing.

C is absent from both; Sc is two branched, and the large space between the first veinlet across the costal space and the humeral is a constant feature. In both, M arises from R, whilst this latter is typically two-branched, R₁ always being straight and undivided. Rs, however, in brachypterous forms may or may not divide; if it does, it usually bifurcates into R₂ + ₃ and R₄ + ₅. M is two-branched, but in brachypterous forms M₁ + ₂ may fuse distally with R₄ + ₅. Cu bifurcates into Cu₁ and Cu₂, the former, however, in the normal wing has accessory veins, which are usually lacking in the abnormal. The remaining veins are all similar, and cross-veins occur irregularly in both.

Hindwing.

The veins in these are similar except in the case of R and M. M, in the brachypterous forms, may or may not be branched into M₁ + ₂ and M₃ + ₄, and when this latter occurs, M₁ + ₂ may fuse with R₄ + ₅, while M₃ + ₄ is always fused with Cu₁. Only the former fusion has been observed as a variation in the normal wing. In the brachypterous type cross-veins are developed to a much less extent.

The venation of brachypterous male on the whole conforms with that of the normal male, but is much more variable. The distal branching of Rs, M, and Cu show the greatest variation, and the development of cross-veins is greatly reduced.