100 



The Mechanism of Evolution in Leptinotarsa 



In figure 4 I have shown in condensed schematic form the results of this 

 study of L. diversa at the source of material at Orizaba and of L. signaticollis 

 at Cuernavaca, through the years 1904 to 1909. This study of the form-index 

 in each of the two sources of materials shows clearly that the condition is not 

 only stable for the species in the location, but also that, taking the location as a 



2.600-2.6')9 



Pig. 5. — Diagram of apparatus for control of relative humidity in the breeding 

 room. The figure shows the complete apparatus. (For explanation of Its parts and 

 working see description in the text.) 



whole through the period of observation, it has the same index as determined 

 from the random samples shown in figure 3. Some divergence of the polygons 

 of distribution in each of the species is shown for the species mode in different 

 years, but no divergence of this sort has been found to have any permanency. 



