STUDIES OF VARIATION IN INSECTS 



275 



left or right elytron or both showing longitudinal confluence 

 (fig. 50, F and G). 



The following frequency polygon represents these fre- 

 quencies graphically : 











FIG. 51. Frequency polygon of the variation in elytral pattern of 905 speci- 

 mens of the flower beetle, Diabrotica soror, collected at Stanford University, 

 October, 1901. 



A second series of 906 individuals was collected just one year 

 later, /. e., October, 1902, from the same chrysanthemum gar- 

 den that furnished most of the first series (1901) and examined 

 and classified as follows : 



Class A: 313 individuals with all spots separate. Class B: 

 40 individuals with left middle pair cqnfluent. Class C : 55 

 individuals with right middle pair confluent. Class D : 388 in- 

 dividuals with both middle pairs confluent (the mode). Classes 

 E, F, G and H : 109 individuals with left or right or both 



