I OUR GRAY SQUIRRELS 29 
effect of natural selection in adapting the animal 
(in color) to its surroundings, by tending to make: 
it less conspicuous in an exposed than in a con- 
cealed habitat, is also to be considered here. 
Quite distinct from this, however, seems to be 
the tendency to melanism, which is so strongly 
marked in several of our sciurids. Among flying- 
squirrels, red squirrels, and chipmunks, a black 
one is as rare as an albino — probably more rare; 
but in the cases of the gray and the fox squirrels 
black examples are extremely common in some 
parts of the country, and are popularly considered 
a wholly separate species. But no such rule of 
climate as mentioned above seems to control this 
phenomenon, since black or dusky forms of both 
species are as likely to be southern as northern in 
their habitat. Where melanism occurs, it is likely 
to prevail over a considerable district, sometimes 
nearly if not quite to the exclusion of squirrels of 
the normal tint. This shows that, though sporadic, 
it “runs in families,” descending from parents to 
young ; yet not inevitably so, for many litters pro- 
duced by black parents will contain a member or 
two gray, or red, or grizzled, and black and normal 
individuals mate freely. The “color-line”’ is not 
drawn in sciurine society. Black ones, however, 
are never, or very rarely, seen east of the Hudson 
River; and, furthermore, the northeastern black is 
often rusty or brownish in tone, rather than pure, 
especially in its summer pelage. 
