314 THE BIOLOGY OF THE SEASONS 



IV 



To the cold and the scarcity of food which Winter in- 

 volves in this and more northerly latitudes there is great 

 variety of response or reaction on the part of living creatures. 

 Of this variety let us take a few illustrations. Thus most 

 of our birds, emblems of freedom, escape the spell by 

 flight ; and, though death is often fleeter still and overtakes 

 them by the way, there can be no doubt that the migration- 

 solution is an effective one. Literally, they have no 

 Winter in their year. Among those partial migrants who 

 are hardy enough or foolhardy enough to risk remaining 

 with us in Winter the mortality is often disastrously high. 

 Winter after Winter may be weathered, and then, as we 

 have already noticed, there may be a severe thinning of 

 the ranks. 



Other creatures, unequal to the long and adventurous 

 journeys of the birds, retire into winter-quarters, in which 

 they lie low, awaiting happier days. Thus the earth- 

 worms burrow more deeply than ever below the reach of 

 the frost, the lemmings tunnel their winding ways beneath 

 the icy crust of the Tundra, all manner of insects in their 

 pupa-stages lie inert within cocoons or other protective 

 envelopes in sheltered corners, the frogs bury themselves 

 deeply in the mud of the pond, and the slow-worms coil 

 up together in the penetralia of their retreats all trying 

 to get below the deadly grip of the frost's fingers. 



Others, again, such as the Arctic fox, the mountain hare, 

 the ermine, the Hudson's Bay lemming, and the ptarmigan, 

 face the dread enchantment of Winter, but turn paler and 

 paler under the spell, until they are white as the snow 

 itself a safety-giving pallor. They have a constitutional 

 tendency to change their colour, and the external cold 

 pulls the trigger that sets the process at work. It is well 



