100 



University of Calif or nia PuUications. [Entomology 



The costa had been crushed in the region of lines 4-6, but 

 otherwise the wing is normal. The character of some of the 

 irregularities here indicated is shown much more clearly on 

 the accompanying figure of a fragment of the same wing (Fig. 



FIG. 83. Fragment of the wing of Hexagenia hilineata, sliowing by 

 contour Unes and shadings the heights of the various portions of the 

 wing. The unshaded areas are the highest, and the solid black the 

 lowest. 



33). This shows the region between the primary vein and the 

 first strong convex vein behind it, the one indicated by the 

 twelfth column of the above taV)le. The levels are shown by 



contour lines, the 

 black and shaded 

 portions being lower 

 than the unshaded 

 part, as the figures 

 in the table indicate. 

 These data show 

 that there is without 

 question more in this 

 matter than alter- 

 nate veins of differ- 

 ent character. The 

 mechanical problem 

 of producing the 

 adequate stiffness of 

 the wing is the most 

 important factor. 



Aside from the 

 matters already dis- 

 cussed and those 



FIG. 34. Abnormal venations in Ephemerid:e after arising OUt of the 

 Eaton. A, Palingenia. B, Elassoneura. C, Callibsetis. j„„*.;,,,, ^f +u^ k4„ j 



D, Cxnis. reduction oi tne nind 



