290 ROBERT M. YERKES 



TABLE 1 



Results of Successive Tests of First Generation, F 1( (Narrow X Wild) 



Hybrid Rats 



Rat Age Date Savageness Wildness Timidity 



19$ 58 days Sept. 25 5 4 4 



Oct. 2 4 4 3 



"17 3 4 3 



"24 1 2 2 



20? 58 days Sept. 25 5 5 5 



Oct. 2 5 5 4 



"17 5 5 4 



"24 2 3 2 



94? 45 days Aug. 7 1 1 1 



"13 2 2 2 



Sept. 25 1 3 2 



Oct. 2 2 2 



21cT 58 days Sept. 25 5 5 5 



Oct. 2 4 4 3 



"17 3 4 3 



"24 2 3 2 



22c? 58 days Sept. 25 5 4 4 



Oct. 2 4 4 3 



"17 2 3 2 



"24 1 3 2 



80c? 50 days June 20 2 1 



July 5 1 2 1 



Aug. 7 1 1 



"13 



In tables i and 2 are presented, for contrast, typical results 

 obtained with groups of F x (first hybrid generation) males and 

 females and F 2 (second hybrid generation) males and females. 



The individuals of these tables are all the offspring of crosses 

 between narrow tame rats and wild rats. The results indi- 

 cate (1) diminishing savageness, wildness, and timidity with 

 repetitions of the tests; (2) sex differences; (3) marked differ- 

 ences for the two generations. The F t individuals grade much 

 higher, on the average, in savageness, wildness, and timidity 

 than do the F 2 rats. 



The results for seventy-eight F x individuals are summarized 

 in table 3. All of these individuals were the offspring of narrow 

 by wild crosses. The table presents, in the first horizontal line, 

 (a) the average age; (b) the range in age of the group; (c) the 

 average number of tests; (d) the range of tests; (e) the average 



