200 



THE AMERICAN NATURALIST 



[Vol. LII 



as a percentage of that of the body, is to a considerable 

 extent independent of the size of the animal. Larger 

 mice, it is true, have relatively somewhat shorter tails 

 than do smaller ones. But the differences are so slight 

 that they may be overlooked, unless the mean size of the 

 two groups under comparison differs considerably. The 

 relative tail lengths of our four races of mice may be com- 

 pared in the following table. 8 This shows the same rela- 

 tions as were portrayed by the graphs. It also shows 

 that there are no significant differences between the sexes 

 as regards the length of this member. 



TABLE III 



rubidus, <? (84) 104.45 ± 0.38 



rubidus, $ (57) 103.37 ± 0.52 



Berkeley gambeli, <J (26) 81.69 ± 0.55 



Berkeley gambeli, £ (21) 81.76 ± 0.65 



La Jolla gambeli, <$ (99) 84.36 + 0.35 



La Jolla gambeli, ? (45) 83.04 + 0.43 



sonoriensis, <? (75) 81.29 ± 0.44 



The distribution frequencies for these various lengths 

 are represented by the histograms (Fig. 8). From these 

 it is evident that only an occasional Eureka mouse has as 

 short a tail as the longest tailed members of any of the 

 other three races. The latter, however, differ from one 

 another but slightly. 



(4) In respect to foot length likewise (Figs. 9, 10) the 

 Eureka mouse is very distinct from the other three races, 

 while the latter show no significant differences among 

 themselves. It is of interest, however, that in all four of 

 these races the female has, on the average, a slightly 

 shorter foot than the male. If any one still entertains the 



sowing to a slight -change in the manner of measurement, which was 



animals of my series have been rejected from the computations. This proce- 

 dure has affeeted particularly the numbers of the Berkeley series. 



