1«0 THE AMERICAN NATURALIST [Vol. LI 



the loose, sandy character of the soil— where, indeed, any 

 real soil exists— and to the comparative lack of shelter 

 from the prevailing westerly winds. Evaporation here is 

 doubtless more rapid than in the comparatively stagnant 

 air of the forests. 



To my surprise, the footprints of mice and other small 

 mammals were abundant, even on the shifting sands, in 

 the areas of sparsest vegetation. Since these tracks, for 

 the most part, were effaced every day by the wind, the 

 animals must have been present in large numbers. In- 

 deed, it was in or close to the dune region that I trapped 

 most of the twenty-eight Peromyscus. It seems more 

 than possible, therefore, that the predominantly paler 

 shade of the mice dwelling here may be due to the same 

 causes which are operative in producing the yet paler 

 hues of many of the desert rodents. 



What the effective factors are can not yet be stated 

 with certainty in either case. Protective coloration is of 

 course an obvious explanation, but it is one of doubtful 

 applicability in the case of animals which are almost 

 wholly nocturnal in their habits. For this and other 

 reasons it seems more likely that the pale coloration of 

 these mice stands in some more direct relation to the 

 humidity of their immediate surroundings. That it is 

 not, however, a strictly ''somatic" phenomenon, called 

 forth anew in each generation, I have already shown for 

 the desert race, P. m. sonoriensis.^ 



Whether or not the peculiar color of the pelage in the 

 Samoa race is likewise hereditary I have endeavored to 

 test experimentally. Seven living females and a number 

 of males were brought to La J olla in June, 1916. Unfor- 

 tunately, it was not possible to obtain more than two 

 broods of young, comprising three individuals, one male 

 and two females. These animals were carefully examined 

 at the age of five months, in comparison with over forty 

 individuals, derived from tlie redwood stock, which were 



