THE CONQUEST OF THE DRY LAND 217 
become longer and thicker at the beginning 
of winter, and the hairs fall out again in 
spring. The same kind of animal may have 
a thicker or a thinner coat according to the 
temperature of the region in which it lives. 
The tiger, for instance, is perhaps commonest 
in the hot jungles of India, but the same 
species spreads far north to very high-lying 
and very cold regions, and tigers living in the 
north have much thicker and longer-haired 
coats than those in the south. 
A very effective way of meeting the dangers 
of a cold winter after a warm summer is to 
avoid them by going to sleep. This is called 
hibernating, and there are many degrees of it. 
The squirrel, the dormouse, the marmot, and 
many others fall into a light slumber in their 
nests beside the heap of nuts and fruits they 
have laid in, but they wake up and have a 
meal, and even gather in a few more stores 
whenever the sun is bright and the day warm. 
We may take as an example of the heavy 
sleepers our common British hedgehog. When. 
winter approaches he chooses a hole in an old 
wall, or under a hedge, or among tree roots, 
fills it with withered leaves, buries himself 
among these, rolls up into a tight ball, and goes 
