POCKET GOPHERS—GRINNELL 353 
Valley, but west of the river, is angularis again; to the eastward 
of the San Joaquin river flood-bottom is pascalis, chiefly in the 
bottom lands of the smaller rivers making down from the Sierras; 
and higher, on the hard-soiled foothills, is mewa. Bottae is dark- 
est colored of all, pascalis is palest colored in this series; bottae 
is largest, but angularis and pascalis are also large; diaboli and 
mewa are small, the latter smallest. It would appear that the effects 
of varying rainfall, or of cloudiness, or of relative humidity of 
the air, are registered in varying tone of color. And soil texture 
affects size. The trend of the long, narrow area of occurrence of 
each of these races happens to be with the trends both of the 
rainfall belts and the mountain axes. The comparative study of 
the outlines of the ranges of animals brings clues as to the essential 
conditions for the special existence of each animal. 
This matter of coloration of gophers presents a rather bafiling 
problem. The paler colored forms are generally associated with 
arid habitats; the darker colored with jhumid habitats. Bottae 
of the coast belt as compared with the almost white albatus of 
the Colorado delta presents an extreme amount of difference. Is 
the factor which has to do with these diverse conditions of color- 
ation, light, or temperature, or is it humidity of the air? 
Let us remember that whatever the locality, the pocket gopher 
stays fully 99 per cent of its time within the underground bur- 
row; and this burrow in desert territory, as well as elsewhere, may 
run through soil that is nearly or quite saturated with water, 
though, more often, it must be said, in deserts it extends through 
soil of relative dryness. In defense of the theory of concealing 
coloratien, it can be urged that the moment of greatest hazard 
to the animal is the moment when the gopher exposes itself to 
view at the mouth of its burrow in pushing out earth, even though 
the total time involved may comprise only a minute a day. It 
may be that the pallor of the desert-inhabiting gopher, like canus 
or jisheri, in a statistical majority of cases, brings success in elud- 
ing enemies. Not so consistent with this theory is the fact that 
there are dark-colored gophers which inhabit the white sands of 
river valleys in relatively humid and cloudy belts; also there are 
pale gophers in arid territories, which live in very dark-colored 
soil, as in the case of fishgvi in parts of the Mono Lake district. 
While in this particular matter of coloration no immediate explana- 
tion of the differences between the races is forthcoming, yet I have 
confidence that not only this, but each and every other character 
which we find to distinguish races, has its full adaptive justification 
in the scheme of existence. 
