I OUR GRAY SQUIRRELS 27 
but attacks their green husks, and his paws get 
richly stained with their brown juices. His power- 
ful chisel-teeth quickly strip the shagbark nuts, 
but the clinging shucks of the pignut hickory are’ 
cut through. So rapidly does he work that a hard 
dry walnut will be opened and cleaned out in less 
than a minute. Those squirrels that inhabit co- 
niferous forests subsist upon the seeds of the 
spruce and pine. These are procured by snipping 
off the scales, beginning at the butt end of the 
cone and following the spiral arrangement. They 
are also said by a writer in the Bulletin of the 
Nuttall Ornithological Club (VII, 54) to suck sap 
from certain trees. 
Certain differences of size and coat noticeable 
between types of the North American gray squir- 
rel from widely separated parts of the country, 
accompanied by local peculiarities of habit, led at 
first to the naming of several supposed species. 
This doubt in the past as to specific unity well 
illustrates the principle that variations in size and 
color among all North American mammals and 
birds are correlated with geographical distribution, 
and seem to conform to varying conditions of 
climate. In general, it may be said that our ani- 
mals show:an enlargement of peripheral parts, 
that is, have longer limbs, tails, etc., in southern 
latitudes than toward the northern limits of their 
range; that the colors also increase in intensity 
southward; and third, that colors are more in- 
