No. 587] 



CALIFORNIA DEER-MICE 



695 



(the same order holds with respect to their rainfall), we 

 have the series: (1) Victorville, (2) La Jolla, (3) 

 Berkeley and (4) Eureka. Correspondingly, the desert 

 mouse (sonoriensis) is the palest of the lot, while the La 

 Jolla mouse, the Berkeley mouse and the Eureka mouse 

 follow in the order of increasing pigmentation. This 

 relation, when viewed in connection with a wide range of 

 known facts, and with certain experimental data to be 

 noted later, can hardly be regarded as accidental. Any 

 exact quantitative determination of the density of pig- 

 mentation would of course be difficult, and it has not yet 

 been attempted. But the width of the dorsal median 

 stripe of the tail is found to serve in some measure as an 

 index of the extension of the darkly pigmented areas. It 

 is interesting to note, in order of increasing width: 

 sonoriensis (28 per cent.), gambeli (32 per cent.) and 

 rubidus (43 per cent.). (The gambeli considered are 

 from La Jolla.) 



Let us grant then, provisionally, some sort of causal 

 relationship between atmospheric humidity and the quan- 

 tity of pigment in the hair or feathers. Now, aside from 

 our ignorance of the physics and chemistry of the proc- 

 esses here involved, there is still a most important bio- 

 logical question left unsolved: Are these differences in 

 pigmentation between the various geographical races 

 germinal in their origin or are they purely somatic and 

 individually acquired? 



It was but a few years ago that Mr. J. A. Allen 13 was 

 shocked by the very moderate suggestion of President 

 Jordan's 14 that perhaps some of our subspecific differ- 

 ences were "ontogenetic," and not racially fixed. Mr. 

 Allen was shocked, though unable to offer any really sub- 

 stantial evidence in reply. In this uncertainty over so 

 elementary a matter of fact, everybody suggested decisive 

 experiments for some one else to perform, but somehow 

 no one seemed disposed to perform them. At least the 



is Science, January 26, 1906. 

 " Science, December 29, 1905. 



