THE A M ERIC AN NA T U BALI ST [ Vol. LII 



quite independently. There is no single graded series 

 for all the characters, which would lead us to suppose that 

 they are in some way correlated or " linked" together. 



When pigment characters alone are considered, the 

 Berkeley mice are certainly intermediate between the La 

 Jolla and the Eureka ones, and to that extent may be said 

 to "approach rubidus." 10 But this is not true of the 

 length of the tail, the foot or the ear. Indeed, as regards 

 the first of these appendages, the Berkeley race diverges 

 even farther from the Eureka race than does that of La 

 Jolla. 11 



The question whether any of these various character 

 differences may be physiologically or genetically linked 

 together, so as to exhibit concomitant variations, is an 

 interesting one, which I hope, in time, to treat rather 

 fully. But I have already computed coefficients of cor- 

 relation between two pairs of characters, viz.: between 

 tail length and width of tail stripe, and between tail length 

 and foot length. 



In obtaining the former, I have based the coefficients 

 upon the deviations from the mean relative tail length of 

 each race and each sex, taken separately. Of these coeffi- 

 cients, three are positive and five negative. They range 

 from - 0.23 to + 0.09, the mean being — 0.03. Thus, it 

 is plain that there is no appreciable correlation, within a 

 single race, between the width of the tail stripe and the 

 length of the tail, despite the fact that these characters 

 seem to be associated, when certain darker races of the 

 northwest coast are compared with more southward rang- 

 ing forms. 



There is, however, a quite marked correlation between 

 the length of the tail and that of the foot. I do not here 

 refer to the obvious fact that larger animals have larger 



io Osgood, 1909, p. 69. This author likewise states that Berkeley speci- 

 fies of Berkeley mice which were not included in Table III. The two sets 

 were trapped in two different localities in the Berkeley hills. 



