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THE AMEBIC AX XAITUALIST 



[Vol. LII 



ferences between males and females, computed according 

 to a method earlier described by me (1915, pp. 345, 346), 

 are: 



(5) In respect to ear length, we find a quite different 

 set of relations. It is the La Jolla mouse in which 

 these appendages are the longest, the Berkeley mouse in 

 which they are the shortest, while the redwood and the 

 desert animals occupy an approximately intermediate 

 position and scarcely differ significantly from one an- 

 other. It is here to be noted that the two extremes of 

 the series, in respect to this character, have been placed 

 by the systematists in the same ' ' subspecies" (gambeli). 



(6) The counting of the tail vertebra, like the other 

 measurements of skeletal characters, has not yet been 

 completed. I have, however, determined the number in 

 25 specimens each of the Eureka, La Jolla and Victor- 

 ville races. The fifth vertebra, counting from the most 

 anterior one in the sacrum, has been regarded as the first 

 of the caudal series. The averages and the frequency 

 distributions are indicated in the following table. 



The significance of these differences seems highly prob- 

 able, despite the small numbers. That between rubidiis 

 and sonoriensis can hardly be questioned. It seems plain, 

 however, that the differences in tail length between these 

 various races is not accounted for by the differences in 

 the number of the vertebra?. Thus the Eureka mouse 

 has a mean tail length which is 28 per cent, (of the smaller 

 number) longer than that of the desert mouse. The pre- 



