204 



THE WINGS OF NEUROPTERA 



"4. The reduction of media in the fore wing to an apparently simple vein, the base 

 of M3+4, appearing as an oblique cross-vein joining Cui. When this ceases to be oblique, 

 the forking of media is entirely obscured. 



"5. The development of a triangular brace across the basal third of both wings, 

 similar in form but unlike in composition. This is a striking example of parallelism 

 in vein development. This brace is formed about a strong secondary fork in a principal 

 vein. The vein is Cui in the fore wing, M3-I-4 in the hind wing. Beyond the fork this 

 vein in the fore wing fuses with M3-|-<i in such manner and to such extent that the boun- 

 daries between the two are no longer traceable. In the hind wing vein IM3+4 is con- 

 tinued free to the wing margin. 



"The secondary posterior branch is joined at its more or less decurrent tip to the 

 vein behind it — to Cu2 in the fore wing; to Cui in the hind wing — thus forming an 

 elongate and sinuous enclosure or loop in the posterior and basal side of the brace. 



rca 



Fig. 200. — Wings of Palpares aeschnoidcs, var. lihelluloides. 



From the outer end of this loop often a short secondary vein springs forward and 

 outward transecting the area of the fork. Since homologies are diflferent in the two 

 wings while the braces are closely parallel, the parts may be conveniently designated as 

 follows: [See Figure 200.] 



"The entire structure may be called the trigonal brace. 



"The strong fork (in Cu], fore wing; in hind wing M3+4) may be called the trigonal 

 fork. 



"The continuation of the vein beyond the fork may be called the trigonal vein. 



"The enclosure behind the fork may be called the trigonal loop. 



"The curved vein arching forward from near the apex of the trigonal loop may be 

 called the trigonal arc. 



"6. The development of gradate series of cross-veins in four dilTerent wing areas: 



"a) A scries of costal gradates in the costal space before the stigma, these cross- 

 veins connecting in regular series the small branches that spring from vein Sc. [See 

 Figure 156.I 



