292 



ROBERT M. YERKES 



TABLE 3 



Summary of Results for First Generation Hybrids, F x (Narrow X Wild) 



36 F, 

 females 



48.75 



25-81 

 da. 



3.67 



1-4 



Distribution of rats in 

 grades 0-5. 



4.39 





 2 

 

 3 

 8 

 23 



2.5 



3.31 





 3 



7 



8 



12 



6 



4.44 





 1 

 

 3 

 10 

 22 



3.22 







2 



10 



9 



8 



7 



3 . 78 4 . 19 





 

 3 

 11 

 13 

 9 





 1 

 3 

 2 

 12 

 18 



2.64 







6 



13 



7 



3.33 









 10 



8 

 14 



4 



the modal grade, we have, in the case of the first tests for both 

 males and females, 5 as the modal grade. In other words, this 

 group of F x hybrids attain the maximal grade of savageness, 

 wildness, and timidity with modal frequency. 



Turning now to a comparison of the results of table 3 with 

 those for the second generation hybrids as presented in table 4, 

 we discover, first cf all, that the F 2 individuals, numbering one 

 hundred and fifteen, grade very much lower on the average in 

 savageness, wildness, and timidity than do the F x hybrids. A 

 comparison of the results for the two sexes indicates a marked 

 difference in that, whereas the F x females grade higher than the 

 males, the F 2 males grade higher than the females. With re- 

 spect to the distribution of individuals there is a great differ- 

 ence for the two generations, for whereas the F t individuals 

 attain as their mode the grade of 5, the F 2 individuals in no 

 instance attain a grade higher than 2 as the modal grade, and 

 in most cases it is either o or 1. Thus, it may be noted in table 



