105 



FIG. 40. Diagram showing the variations in size of eight different races of 

 paramecium. Each horizontal row represents a race derived from a 

 single parent individual. The individual showing the mean size in 

 each race is indicated by a cross placed above it. The mean of the 

 entire lot is shown at X X. The numbers show the measure- 

 ments in microns. (After Jennings.) 



112 



