204 



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 

 average length (Fig. 44). Nettleship says 



X 105 



Fig. 44. Diagram of eight different races of Paramecium, 

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

 individual showing the mean size in each race is indicated by 

 -j- ; 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 43. (After Jennings.) 



