20 THOMAS SAY FOUNDATION 



three of these were of common occurrence: the others 

 were erratic. 



There is much variation in the position of the cross- 

 veins, y-m and m-cu, in relation to the adjacent forks, af- 

 fecting thus the position of the cord. The crossvein was 

 situated before the fork of the median vein 5 times, and 

 beyond that fork 67 times. Likewise the terminal cross- 

 vein in the intercubital space of the fore wing was situ- 

 ated before the fork of the cubital vein 47 times, opposite 

 that fork 5 times, and beyond that fork 20 times. 



Variation in Neoperla clymene. — This was studied in 

 25 specimens, 13 males and 12 females, collected at 

 Ithaca, N. Y. The variation in the number of crossveins 

 between costal and subcostal vein was as follows : 



No. of crossveins 1 2 3 4 5 6 7 8 9 10 11 12 



Times occurring, fore wing 5 9 10 14 8 4 



Times occurring, hind wing 1 2 2 2 3 11 18 10 1 



Thus the normal number is 10 in the fore wing and 7 in 

 the hind wing. 



The variation in costal crossveins in the apical series 

 was as follows : 



No. of crossveins 12 3 4 5 



Times occurring, fore wing 7 20 19 4 



Times occurring, hind wing 5 20 23 1 1 



Thus, 2 or 3 is the normal number for this species with no 

 material difference for fore and hind wings. 



The variation in crossveins of the median series is as 

 follows : 



No. of crossveins 3 4 5 6 7 



Times occurring, fore wing 2 12 21 12 3 



These are entirely absent from the hind wing. 



The variation in crossveins of the cubital series was as 

 follows : 



No. of crossveins 3 4 5 6 7 8 



Times occurring, fore wing 1 13 14 16 5 1 



Times occurring, hind wing 2 17 22 8 1 



Thus the mode is at 6 in the fore wing and at 5 in the 

 hind wing. 



Only 25 extra crossveins occurred in all these wings, all 

 of them in 12 specimens, and 10 of them in two specimens. 

 All but 6 of them were in the apical radial area. 



The variation in branches of the radial sector was as 

 follows : 



No. of branches 2 3 4 



Times occurring $ and $ 9 84 7 



There was practically no difference between fore and 

 hind wing, nor between the sexes. There was a little 



