92 THE COLOURS OF ANIMALS 



shrimps and prawns bury themselves in the sand by 

 day and swim about at night, exactly like the uninjured 

 animals. 1 



The seasonal change of colour in northern mammals 



The well-known fact that many northern quad- 

 rupeds become white in winter has given rise to a 

 great deal of discussion as to the manner in which 

 the change is brought about. Some have maintained 

 that the animals simply acquire a new coat of white 

 hair which conceals the darker fur beneath, while the 

 long hairs of the summer coat are believed to be shed. 

 Others believe that these latter actually change and 

 become white, and that, although an abundance of 

 new hairs also appear, nothing is shed. Most ob- 

 servers agree that the white hair is shed at the close 

 of winter : this is of course independently neces- 

 sary, in order to reduce the thickness of the winter 

 coat. 



I shall bring forward what appears to be conclusive 

 evidence that the latter view is the right one, at any 

 rate for certain species. But however the change is 

 brought about, it will be rightly considered in this 

 part of the subject, if it can be proved that it is called 

 up either directly or indirectly by the stimulus pro- 

 vided by the external conditions, and is not merely a 

 contemporaneous change, harmonising with those in 



1 L.c. p. 212. 



