28 MAMMALIA. 



outlines and hides their movements, that the larger number do their 

 hunting. Many of them are also out during cloudy days and moon- 

 light nights ; and in winter, when the ground is white with snow, 

 they apparently circumambulate all night long. 



The phenomenon of hibernation, which enables many mammals 

 to endure a climate to the severity of which they would inevitably 

 succumb were they to remain active throughout the year, and to 

 thrive in regions where they would starve during certain seasons 

 but for their ability to become dormant when scarcity of food pre- 

 vails, is well exemplified in a number of our species. The following 

 are known to pass a greater or less period of the winter season in a 

 condition of lethargy : the Bear, Raccoon, Bats, Gray Squirrel, Chip- 

 munk, Woodchuck, and Jumping Mouse. Of these the Woodchuck 

 affords the most remarkable example. With astonishing regularity 

 and precision, and utterly regardless of the state of the weather or 

 condition of his food supply, he sinks into his burrow about the 20th 

 of September, and is rarely seen again before the middle of March. 

 It frequently, indeed usually, happens that the time chosen for enter- 

 ing upon the execution of this singular proclivity is during fine warm 

 weather and at a time when the fields are clothed with a luxuriant 

 growth of his favorite food, clover. In fact the Woodchuck retires 

 to the cold clank recesses of his cheerless subterranean abode to 

 commence a period of voluntary seclusion, to enter upon a state of 

 complete oblivion and absolute lethargy, at the very time when one 

 would naturally suppose he would most enjoy himself above ground. 



The Gray Squirrel, on the other hand, remains out nearly the entire 

 winter and withdraws to its nest, in some hollow tree, only during 

 the severest weather. The Raccoon and the Bear furnish examples 

 of animals whose dormant periods are intermediate in duration be- 

 tween those above cited. 



Hibernation is, after all, merely a profound sleep, intensified and 

 protracted. During ordinary sleep respiration is slackened and 

 the temperature of the body is lower than when the animal is awake. 



