146 
MAMMALIA. 
wholly cut off from food during this period. Thus the gray squir- 
rel, being able to find a certain amount of sustenance when the 
ground is covered with snow, remains dormant during severe cold 
only ; and the chipmunk, which lays up a great store of provision, 
frequently awakes to eat, and is at all times easily aroused ; while 
the Woodchuck, whose food is of such a nature that he can neither 
gather a supply for winter’s use, nor find any were he to go in 
search of it, must needs sleep long and soundly or starve. 
The Woodchuck and the flying squirrel occupy the two extremes 
of the family to which both belong, while the ground squirrels and 
spermophiles hold intermediate positions. The flying squirrel is 
the most highly specialized form, showing the most perfect adapta- 
tion of structure to habit; while the Woodchuck must at present 
be regarded as the most generalized type of the living members of 
the group. These animals are so widely different that, taken 
alone, they would naturally be regarded as pertaining to separate 
families ; but a careful study of the numerous intermediate forms 
not only proves this view to be incorrect, but also shows that the 
gradation of connecting species is so complete that it is even diffi- 
cult, in many cases, to draw the line between genera. 
The Woodchuck lacks the grace and agility of the arboreal 
squirrels, but his heavy body and powerful paws are well adapted 
to his terrestrial mode of life. Both animals are modified, but to 
widely different ends. 
Woodchucks are both nocturnal and diurnal, the periods of feed- 
ing being determined, in a general way, by the time of the year, 
the weather, and the proximity and nature of enemies. In summer, 
throughout the farming districts, they commonly leave their bur- 
rows early in the morning, late in the afternoon, and during moon- 
light nights ; but may sometimes be found abroad at all hours. As 
autumn approaches, and they become more and more fat and sleepy, 
they usually appear only in fine weather, and then but for a few 
hours in the hottest part of the afternoon. 
