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 
