MIDWINTER 131 



degrees of perfection, to adjust the internal produc- 

 tion of heat to the external loss of it, and thus keep 

 an approximately constant body-temperature all the 

 year round. In some mammals in which this 

 " thermotaxis " arrangement is less perfect than 

 usual, there is a breakdown when the cold comes 

 on. The creature gives up the contest and sinks 

 into deep slumber in some confined space, to the 

 temperature of which that of the sleeper approxi- 

 mates. If the external temperature does not fall too 

 far, this hibernation may be life-saving. Similar, 

 but less effective, is the lethargy of cold-blooded 

 animals like tortoises and frogs, the vital collapse 

 of snails and chrysalids, and the inactivity of many 

 humble creatures in sheltered nooks and crannies. 

 They evade the winter by their extreme passivity; 

 they cannot carry on, but they do not die. 



We are led to think of stores, whether inside the 

 body in the form of fat which may be slowly burnt 

 away in winter months, or outside the body in the 

 form of nut-pits, seed-granaries, meat-larders, and 

 what not. The climax on the instinctive tack of 

 evolution is to be found in the societary stores made 

 by ants and bees. Of another solution we are 

 reminded by the ptarmigan and the hare that we 

 startled, good examples of creatures that turn 

 pale under the spell of winter till they are white 

 as the snow itself. The white cloak may help in 

 concealment and in the chase; it also furnishes the 

 physiologically most comfortable dress for a warm- 

 blooded animal in very cold surroundings. We 



