No. ()03j 



THE HOLE OE ISOLATION 



183 



Eureka region in regard to both the length of the tail and 

 that of the ear. In respect to the former character, they 

 agree pretty closely with the Samoa race, the difference 

 from the redwood stock being statistically even more cer- 

 tain in this case. To still further complicate the situation, 

 we find that the ear, instead of being longer, is shorter 

 than that of the redwood mice by about half a millimeter, 

 and thus averages about one and one half millimeters 

 shorter than in the peninsula race. Here, too, the dif- 

 ferences are even more certain statistically than those 

 which distinguish the Eureka and Samoa series. 



The numbers are small, of course, only twenty-eight 

 of the Little Eiver mice having been available for meas- 

 urement. But as regards tail length, the ditference be- 

 tween the averages is seven to nine^*^ times its probable 

 error, so that the likelihood of its being due to random 

 sampling is very small. 



Have we, then, here merely another example of incon- 

 clusive data, which might best have been left unpublished? 

 I do not think so. The mere existence of these local dif- 

 ferences in color and in the size of parts deserves careful 

 description, whatever interpretation we may place upon 

 them. 



Moreover, I am disposed to believe that the case of coat 

 color is not entirely comparable with that of the length 

 of the appendages. In another article^ ^ I have given 

 reasons for thinking that some of the differences in the 

 former may have arisen in nature as more or less direct 

 effects of environmental conditions. On the other hand, 

 I have shown that such an explanation would be of very 

 difficult application as regards some of the measurable 

 differences in the parts of the body, even though the latter 

 are known to be readily influenced by various experi- 

 mental agencies. 



Now the evidence at hand is sufficient to show that any 

 environmentally produced modifications of coat color are 



10 Depending on whether the comparison is made with the Eureka males 

 or females, the sexes being combined in the case of the Little River group. 



