Nos. 618-619] INHEBITANCE IN PEEOMYSCUS ' 



2«)7 



nearly midway between the mean widths found in the 

 parent races. (2) There is no increase in the variability 



TABLE VII 



of tliis character in the F 2 generation. Indeed, the stand- 

 ard deviation for the latter animals chances to be the 

 lowest of the four values given. 



It seems worth while to indicate the actual distribution 

 frequencies of the tail-stripe measurements for these four 

 groups of mice (Table VIII). 



TABLE VIII 



In contrast to this case of the tail-stripe, it is interest- 

 ing to note that, in respect to relative tail length, the F 2 

 generation shows a somewhat higher variability than the 

 F a generation or than either of the parent races. But it 

 so happens that this is a character in which the parent 

 races do not appreciably differ. 



In reality, it is probable that none of these differences 

 in variability is significant, in view of the small numbers 

 of individuals concerned. The explanation offered for 

 certain differences between other hybrids to be discussed 

 later— namely, that the F\ and F 2 generations differed in 

 the relative degree of abnormality— does not seem to ap- 

 ply here. The mean body length is about equal in the 

 two generations, as well as the mean length of tail and 

 foot. 



The crosses between the Eureka and the La Jolla races 

 have not been carried far enough to render any report 

 upon them possible at present. 



