118 SECRETS OF ANIMAL LIFE 



collecting of blankets against the winter's cold, as 

 is illustrated by the non-conducting scales around 

 the buds, by the sleeping-sacks which caterpillars 

 fashion before sinking into their chrysalid lethargy, 

 by the soft quilts gathered into their winter resting- 

 places by dormice and other true hibernators. The 

 blanching of mountain hare and ptarmigan is also a 

 protective preparation. In the fourth place, there 

 is what one may dare to call the circumvention of 

 difficulties. The clearest illustration is in the 

 migration of the majority of North Temperate birds 

 to comfortable winter quarters in the South. They 

 evade impending disasters so triumphantly that 

 they know no winter in their year. Or, again, in 

 true hibernation of hedgehog and bat, dormouse 

 and marmot, there is a relapse from the normal 

 " warm-bloodedness," a seasonal sinking back to- 

 ward an ancestral " cold-bloodedness," which leaves 

 the creature less open to the assaults of the winter; 

 able, indeed, to defy them, especially within a 

 secluded, confined, and often well-blanketed sleeping 

 chamber. Even in the lethargy of tortoise and frog, 

 snail and chrysalid, which must not be mixed up 

 with true hibernation (confined to a few mammals), 

 there is the same general idea of relapse into a 

 condition of " lying low " physiologically, which 

 renders the creature much less open to attack. The 

 fire of life, well banked up, almost smothered in its 

 own ashes, burns very low through the night of 

 winter, and " keeps in." No doubt the fall of the 

 year means retrenchment and sacrifice, retreat and 



