STRICTLY INCOG. 55 



cover him and pounce down upon him off-hand ; while, 

 conversely, the fox himself, if red or brown, could never 

 creep upon the unwary hare without previous detection, 

 which would defeat his purpose. For this reason, the 

 ptarmigan and the willow grouse become as white in winter 

 as the vast snow-fields under which they burrow ; the 

 ermine changes his dusky summer coat for the expensive 

 wintry suit beloved of British Themis ; the snow-bunting 

 acquires his milk-white plumage ; and even the weasel 

 assimilates himself more or less hi hue to the unvarying 

 garb of arctic nature. To be out of the fashion is there 

 quite literally to be out of the world : no half-measures will 

 suit the stern decree of polar biology ; strict compliance 

 with the law of winter change is absolutely necessary to 

 success in the struggle for existence. 



Now, how has this curious uniformity of dress in arctic 

 animals been brought about ? Why, simply by that un- 

 yielding principle of Nature which condemns the less adapted 

 for ever to extinction, and exalts the better adapted to the 

 high places of her hierarchy in their stead. The ptarmigan 

 and the snow-buntings that look most like the snow have 

 for ages been least likely to attract the unfavourable atten- 

 tion of arctic fox or prowling ermine ; the fox or ermine 

 that came most silently and most unperceived across the 

 shifting drifts has been most likely to steal unawares upon 

 the heedless flocks of ptarmigan and snow-bunting. In 

 the one case protective colouring preserves the animal from 

 himself being devoured ; in the other case it enables him 

 the more easily to devour others. And since 'Eat or be 

 eaten ' is the shrill sentence of Nature upon all animal life, 

 the final result is the unbroken whiteness of the arctic 

 fauna in all its developments of fur or feather. 



Where the colouring of nature is absolutely uniform, as 

 among the arctic snows or the chilly mountain tops, the 



