74 



ANIMAL COLORATION. 



are offered by the raven on the one band and tbe Arctic fox 

 on tbe otber ; it does undergo a certain amount of change at 

 the beginning of winter, becoming not white, but greyer. 



Sometimes closely allied forms show a difference in their 

 susceptibility to these climatic changes. One species of hare 

 turns white in the winter, another does not. 



The Hudson's Bay lemming (Cuniculus torquatus) under- 

 goes the change of colour, but its near relation the Scau- 



Fis. 1. -Arctic 



dinavian lemming (Jft/ocks lemmas) does not undergo this 

 change. The principal animals which change to white in 

 winter, in addition to those already referred to, are the 

 ptarmigan, the American hare (Legits americanus), the ermine 

 and stoat. With regard to the Arctic fox (Cant's lagopus) it 

 has been stated* that this animal does not alter its colour 

 according to the season, and that the change is merely a 

 question of age and sex ; only the old males are white, and 

 * Trouessart," La GeogrdpTiie Zoologique" Paris, 1890, p. 29. 



