38 



CHARLES A. COBURN 



this case are 0.0071 grade for wildness and 0.0067 grade for 

 savageness. These represent the grade-lowering effect of 

 age and the presence of the experimenter exerted each day on 

 the mice of Fib when they receive their first test at the average 

 age of 53 days. Likewise the rates per day for wildness and 

 savageness of the younger mice of Fb are, respectively, 0.0328 

 grade and 0.0309 grade, and for the older mice of F2b, 0.00075 

 grade and 0.00829 grade. It would thus seem that age and 

 the presence of the experimenter have an effect in lessening the 

 grade of wildness and savageness of the mice inversely in pro- 

 portion to the age of the mouse, providing the first test is given 

 when the mice are between 33 and 60 days old. The rates ac- 

 cording to sex are as follows: 



From these results it is seen that the females had a higher 

 rate of decrease per day for both wildness and savageness ex- 

 cept in savageness of the Fib and the F2b (Old), in which cases 

 it was zero for the former and a negative quantity (0.00339) 

 for the latter. 



C. Results from crossing wild females with tame males in com- 

 parison with the results from crosses of tame females 

 with wild males 



The hybrids used by Professor Yerkes in his study were 

 all obtained by crossing tame female rats with wild male rats. 

 It was to neutralize the effect due to the possibility of the par- 

 ent of one sex exerting a stronger hereditary and environmental 

 influence on the offspring than the parent of the opposite sex 

 that the first generation hybrids of both series of this study were 

 obtained about equally from wild females crossed with tame 



