STUDIES OF VARIATION IN INSECTS 



303 



females 12 to 16. The mode for the outer row in both males 

 and females is 12, for the inner row 12, with 13 nearly as fre- 

 quent. Although the series are too short to afford fair con- 



FIG. 64. Frequency polygon of the variation in number of spines in the 

 inner row on right tibiae of 36 male red-legged locusts Melanoplus femur-rub rum. 



elusions from statistics, it is obvious that the frequency and 

 range of the numbers of spines above the mode are larger than 



FIG. 65. Frequency polygon of the variation in number of spines in inner 

 row of left tibiae of 39 male red-legged locusts, Melanoplusfemur-rubrum. 



those below the mode, indicating the course of evolutionary 

 movement. 



