FLYING SQUIRRELS. 89 



excavation, the woodchuck will sometimes take up its abode in rocky ledges or in 

 the hollow roots of trees. During the summer the greater number of these animals 

 live in the open fields ; but in the winter it appears that in the Adirondack region 

 at least they retire for the winter to burrows situated close to, or actually within, 

 the borders of woods. In the Adirondack^ the woodchucks become very fat in the 

 early autumn, and retire for their winter sleep — no matter what be the temperature 

 or the state of the weather — about the equinox, from which they do not awake 

 till the middle or latter part of March. Still more remarkable is the circumstance 

 that the animal often retires when the weather is genial and food abundant, while 

 at the time of its reappearance the ground is frequently deep in snow. 



" Woodchucks," writes Dr. Merriam, " are both nocturnal and diurnal, the 

 periods of feeding being determined, in a general way, by the time of the year, the 

 weather, and the proximity of enemies. In summer, throughout the farming 

 districts, they commonly leave their burrows early in the morning, late in the 

 afternoon, and dining moonlight nights ; but may sometimes be found abroad at 

 all hours. As autumn approaches, and they become more fat and sleepy, they 

 usually appear only in hue weather, and then but for a few hours in the hottest 

 part of the afternoon." Like the Old World species, the woodchuck when much 

 hunted becomes exceedingly wary and difficult to approach; but it differs from all 

 the latter in that it will sometimes ascend trees and shrubs — making these ascents 

 sometimes for pleasure and at others to avoid foes. Woodchucks live either singly 

 or in pairs : tin- young, which arc horn .'it t lie end of April or beginning of May in 

 the Adirondack district, remaining with their parents only a few months. The 

 number in a litter is usually from four to six. When the young iirst leave their 

 parents they take refuge in stone walls, hollow logs, or even hollow trees — habits 

 quite different from those of their Old World cousins, and showing a marked 

 approximation towards the chipmunks. 



In some parts of New Hampshire woodchucks are so numerous as to cause 

 serious inconvenience to agriculturists, and rewards have consequently been offered 

 by the State for their destruction. 



Extinct Marmot- Remains of extinct species of susliks occur in the higher 



like Rodents. Tertiary rocks of Europe ; in addition to which the Upper Eocene 

 beds of France yield evidence of an extinct but apparently allied genus, known as 

 PlesispermophiluS. More primitive are the forms described as Plesiarctomys, 

 which, while showing certain resemblances both to the marmots and the squirrels, 

 have triangular three-cusped upper molar teeth, and no bony process defining the 

 hinder limit of the upper border of the socket of the eye. These Eodents are 

 found in the Middle Tertiary deposits both of Europe and North America. 



The Flying Squirrels. 



Genera Sciwropterus, Pteromys, and JEupetaurus. 



The flying squirrels of the Northern Hemisphere, which are divided into the 

 three generic groups named above, are sufficiently characterised by possessing a 

 parachute-like membrane extending from the sides of the body to the toes, and 



