VOL. I. ] Colors of West Coast Mammals. 211 
upon the tenability of the theory of physiological selection, about 
which scientists have not yet reached any unanimity, fascinating 
and plausible as it certainly appears. If incipient species are sterile 
when crossed, then any markings which would enable the individuals 
readily to distinguish their own kind from the allied form would be 
an advantage, and it would seem that natural selection would en- 
courage it. Weare here stopped again by the question: What if 
the two incipient species did cross and the result prove to be infer- 
tile? Would this be a disadvantage to the individuals concerned, 
or to the race ingeneral? Clearly to the race and not to the partic- 
ular individuals. But if this be the case, how could natural selection 
favor these markings any more than it could the ones previously 
considered ? 
There are some interesting examples of recognition markings 
among west coast mammals, one of the most striking being the an- 
telope squirrel ( Zamias leucurus), to which Dr. C. Hart Merriam 
has already called attention.* Following are his words: “ The 
antelope squirrel and its geographical races afford striking illustra- 
tions of the exhibition of two principles of color adaptations com- 
___ bined in the same individual. When at rest the animal is seldom 
seen, its color and markings being in complete harmony with its 
- surroundings, in obedience to the law of protective coloration. But 
pee the instant it starts to run, the tail is elevated and its conspicuous 
white under-side is turned towards the observer, forcing itself upon 
the eye whether on the lookout for it or not.’’ This is clearly a 
~ ease of directive coloration, and I am at a loss to consider in what 
other manner this marking could be construed. Any one who has 
: seen a party of these little chipmunks skurrying away across the 
desert with their white tails elevated must admit that so conspicuous 
a marking can only be explained as a means for enabling the lag- 
_ gards and stragglers to travel with the main body of the party 
away from danger. Harris’ chipmunk ( Zamias harrisi) resembles 
the preceding species very closely, the only conspicuous difference 
being that it has the under surface of the tail black instead of white. 
~ Having never seen this species alive, it is impossible for me to say 
how conspicuous this black under tail would be in a state of nature, 
but it certainly cannot be as conspicuous as the white tail. This 
iy * North American Fauna, No. 3, p. 52- 
