198 HEREDITY AND ENVIRONMENT 



each race and were of course inherited. Jen- 

 nings has found races of Paramecium which 

 show hereditary differences of .005 mm. in 

 length (Fig. 44). Nettleship says that the 



Fig. 44. Diagram of eight different races of I'aram.eciimi, 

 each horizontal row (A — H) representing a single race. The 

 individual showing the mean size in each race is indicated by 

 -[- ; the mean of all the races is shown by the line X — X. 

 The numbers are- the lengths in micra (-thousandths of 

 a millimeter), X ^3. (After Jennings.) 



