750 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



daughters showed a productiveness just about equal to that of the A' sub- 

 family under the same conditions. The average brood of the cross-bred 

 mothers was 237, that of the purely mated A' mothers was 242. 



TABLE III. 



Effect of Crossing Races M and N, each Inbred for Twenty-four 



Generations. 



TABLE IV. 



Effect of Crossing Races A and M, Inbred for Fifty-five and 

 Twenty-four Generations respectively. 



TABLE V. 



Effect of Crossing Races A and N, Inbred for Fifty-five and 

 Twenty-four Generations respectively. 



