NUMBER XXXIX 

 THE WHITE WINTER COAT 



WHEN winter draws near we think of a change 

 of dress. We clothe ourselves in the skins 

 of other mammals, putting on layer after layer 

 of wool, and, it may be, a fur coat on the top. 

 Similarly many mammals grow a thicker and longer 

 coat of hair as the days become colder. But there 

 is also in some creatures a change of colour to white, 

 as we see it, for instance, in the mountain hare, 

 among mammals, and in the ptarmigan, among 

 birds. How does this change come about, and what 

 is its meaning ? 



Changing to white in winter is exhibited by dis- 

 tinctively northern creatures the Arctic fox, the 

 Hudson's Bay lemming, the ermine, the mountain 

 hare, the American hare, and the ptarmigan. This 

 is interesting, since permanent whiteness is charac- 

 teristic of many northern animals, such as Polar 

 bear and American Polar hare, Greenland falcon, 

 and snowy owl. It is likely, therefore, that chang- 

 ing to white is advantageous for the same reasons 

 as permanent whiteness. 



Some of the mammals that usually turn white 

 do not always change, and this is connected with 



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