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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



illary affects the anterior group of veins in the same manner as does 

 the corresponding plate of the forewing. 



When the distal part of the third axillary is lifted by the pull 

 of the flexor muscle, the median plate turns the preanal area of the 

 wing posteriorly and toward the body, and at the same time deflects 

 it to an almost vertical position, with the costal margin downward. 

 The wing surface makes a double fold along the vena dividens (figs. 

 45 B, 50 B, VD), and the area between the vena dividens and the 



AF lA 2A 3A 



2Cu 



^--iCu 



R+M 



S" 



Fig. 50. — Positions of the flexed wings of Dissosteira. 



A, vertical cross-section through fourth abdominal segment, with wings folded 

 over body, seen from behind. B, section of right hind wing more enlarged. 



lA, 2 A, ^A, 7 A, first, second, third, and seventh primary anal veins; AF, 

 anal fold ; C, costa ; iCu, first cubitus ; 2Cu, second cubitus ; /, intercalary vein ; 

 i, j, secondary veins of first anal plait ; k, first concave anal vein ; /, second con- 

 cave anal vein ; M, media ; R, radius ; R -]- M, combined basal shafts of radius 

 and media ; S, sternum ; T, tergum ; VD, vena dividens. * 



first principal anal vein {lA) is folded outward beneath the preanal 

 area, with the secondary vein k in the ventral angle of the fold (fig. 

 50 B). While these maneuvers are taking place in the anterior and 

 middle parts of the wing, the anal fan is bent downward as it comes 

 against the side of the abdomen, and its ventral surface is turned 

 outward beneath the deflected preanal area. The membrane of the 

 fan is plaited between each two of the first seven principal anal veins 

 (fig. 50 B, lA-yA), with the secondary veins occupying the ventral 

 lines of the folds. The posterior part of the fan spreads out against 

 the upper part of the side of the abdomen (A). 



