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- 



