98 



The Mechanism op Evolution in Leptinotaesa 



The form-index of the two species was first determined from a series of 

 random samples, and the results are shown graphically in figure 3, showing the 

 low range of variability of the value, as well as the distinct grouping of the two 

 species about separate modes. The overlapping of the two polygons does not 

 seem to have more than the significance of ordinary fiuctuating variations of 

 integral variates, and although the attempt has been made to breed pure lines 



L. signaticollis. 



Fio. 3. 



from the extremes of these polygons, no results have come therefrom, so that as 

 far as experience goes the value is a single one, with the fluctuation common in 

 graduated varieties. 



In that this first determination was made upon materials from many localities 

 and in different years, confessedly heterogeneous materials as regards genetic 

 relationships, a second study was made upon materials from the two locations 

 most used as the source of materials for this work. 



