22 THOMAS SAY FOUNDATION 



terms of the r-m crossvein (whether it is in or out in re- 

 lation to crossvein r) was as follows : 



Ajog in ereet out 



Times occurring, fore wing 34 9 7 



Times occurring, hind wing 5 5 41 



Variation in Isoperla bilineata. — This was studied in 

 24 specimens, 12 males and 12 females, collected at Old 

 Forge, N. Y. 



The variation in crossveins in the space between costal 

 and subcostal veins was as follows : 



Xo. of crossveins 3 4 5 6 7 



Times occurring, fore wing 3 15 26 33 1 



Times occurring, hind wing 25 23 



Thus the mode in the fore wing was 5 and in the hind 

 wing 3. 



The variation in crossveins in the apical space was as 

 follows : 



No. of crossveins 1 2 3 



Times occurring, fore wing 30 17 1 



Times occurring, hind wing 40 7 1 



Thus a single crossvein is the mode for both wings. 



The variation of crossveins in the median space was as 

 follows : 



No. of crossveins 12 3 4 5 6 



Times occurring, fore wing 8 20 9 1] 



Times occurring, hind wing 47 1 



Thus 5 is the mode for the fore wing while in the hind 

 wing they are normally lacking. 



The variation in crossveins in the intercubital space 

 was as follows : 



No. of crossveins 12 3 4 5 6 7 



Times occurring, fore wing 2 17 20 8 1 



Times occurring, hind wing 43 5 



Here again the mode for the fore wing was 5, and as in 

 the preceding the ranges of variation for fore and hind 

 wings did not overlap. 



The crossvein m-cu was present in a third of the wings 

 and had disappeared by fusion in the other two-thirds. 

 The fusion was for a distance about equal to the length of 

 the radial crossvein in most cases but it was often longer 

 and in one wing it extended to the wing border. 



The matchings of the two crossveins of the cord, r and 

 r-m, upon the radial sector was as follows: 



Jog of r-m in relation to r in erect out 



Times occurring in fore wing. 6 13 29 



Times occurring in hind wing 3 9 36 



The branches of the radial sector were 2 (a single fork) 



