754 



PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi 



of it, are two parallel veins, separated by a single row of cells, anal 

 ogou's to the veins 31^ and J/^ in the Odonata. (3) Behind these is si 

 transverse bracing of the basal part of the wing, analogous to the 

 trianole in the Anisoptera, and to the special braces beyond the quad 

 ranfflc in Z(n\^ and Jletxrlna. 



^^ XJfi^. 



Fig. 42.— Diagram (hypothetical) of the evolytion of a brace for a unilateral fork; 1, 2, 3, 



SUCCESSIVE stages. 



We have shown that the brace vein to the stigma and the supple 

 nients, etc., arc independently developed in several groups. We hav( 

 shown that the sectors interpolated between the tips of veins in severa 

 oroups have become attached to veins, making the latter appear forked 

 bur illustrations of this were veins /i-v in the Aeschnin*, and vehi 

 i/g and M^ in Clialmpteryx (fig. 22) ; but if one wishes to see how fa 



Fig. 43. — Wings of Ncurobash kaiipii Brauer. 



this process has been carried on independent lines, let him examiii 

 such wings as those of Megaloprepus (fig. 37) and Vestalis (fig. 41). 



There is one frequent tendency toward purel}' mechanical improve 

 ment of which we have given but a single example— the bridge, joinin 

 the radial sector to vein M^^^. It is manifest alwaj^s in a brace ( 

 the same kind as the one which we have technically designated as th 

 bridge, and is formed at a point where a branch springs from the sid 

 of a straight vein and then bends parallel. The accompanying diagrai 



