VOL. II. | Colors of West Coast Mammals. —=—.203 
some other. It is sticky, not powdery, and seems to adhere to the 
cell walls unless artificially removed. 
This paper aims to be suggestive rather than convincing, and 
especially to show how much more remains to be learned than has 
_ yet been discovered. 
NOTES ON THE COLORS OF WEST COAST MAMMALS. 
BY CHARLES A. KEELER. 
In considering problems in the domain of evolution, it is neces- 
sary to recognize the frequently slighted fact that natural selection 
is never creative, but simply selective in its workings. Every modi- 
fication in an organism must have some more fundamental factor to 
originate it, upon which natural selection may subsequently act. 
Whether we recognize with Spencer the Lamarckian factors of use 
and disuse, or follow Weismann and Wallace in excluding the in- 
: _ heritance of acquired characters, we must agree in positing individ- 
- ual, and what, for lack of a more significant name, has been called 
a fortuitous variation, as propensities of organic beings, without which 
: natural selection would be impossible. But it still remains to be 
aks accounted for why the tendency to vary is directed along definite 
lines, and the answers commonly given to this question seem insuf- 
ficient to explain it. 
Taking a concrete example of this from west coast mammals, the 
_ black-headed ground squirrel of Lower California ( Spermophilus 
grammurus atricapillus) belongs to the same group as S. grammu- 
rus beecheyi, of central California, into which variety it shades by 
insensible gradations. It is distinguished from the latter roughly - 
by the darker color of the back, especially of the anterior parts, 
which in typical specimens are black. From characteristic lo- 
poe calities the black is very constant, and so strongly marked as to 
_ make a strikingly distinct species were there no intergradations 
_ in other regions. Now some shade of brown or gray was in all 
_ probability the original color of this species, judging both from 
_ the fact that these colors are naturally more primitive than black, 
that the black races are more local than the lighter ones, and that 
_ the young are much paler than the adult. It then becomes proper 
to ask how this black color has been derived. eee 
Mr. Walter E. Bryant, who discovered the race, says that it is 
