82 THE PTARMIGAN. 



find it pretty generally extended ; birds and rapacious 

 animals become lighter in winter ; and so does the old 

 hair upon cattle, and other quadrupeds, that are left out 

 for the winter in exposed situations. The ermine, 

 which does not need much protection, except from 

 man, becomes white in winter ; and many animals that 

 are dark on the upper part of the body, are light, or 

 were white on the under, that an equal temperature of 

 the vital parts may be preserved. 



This curious seasonal change has not been very 

 carefully investigated ; and, therefore, the precise way 

 in which it is brought about cannot be ascertained. 

 Attempts have been made to explain it, by urging that, 

 when animals are exposed to strong light and heat, the 

 deoxydising rays of the sun decompose carbonic acid, 

 and as that is given out at the surface, the carbon is 

 precipitated upon the rete mucosum, and produces the 

 black colour ; but the lips and tips of the ears in the 

 alpine hare retain their blackness in winter ; and there- 

 fore the several parts of the skin would require to be 

 endowed with different powers ; and in the grouse of 

 Labrador, the feathers of the tail remain black during 

 the winter, as do some feathers on the breast of 



THE PTARMIGAN. 



THE PTARMIGAN, rock grouse, or white partridge, 

 (Tetrao lagopusj) which is another inhabitant of the 

 most elevated parts of mountains ; and, except in lofty 

 and lonely places, it is rather a rare bird. It resembles 

 the common red grouse in form, only it is, perhaps, a 

 little less, the length being about fifteen inches, the 

 breadth two feet, and the weight nineteen ounces. 



