THE MOUNTAIN OR BLUE HARE 321 



Physiological necessities, chemical and climatic, 1 rather than 

 the need of being inconspicuous, appear to have been the 

 factors responsible for the evolution of these divergent pelages. 

 Indeed it looks as if any shade of grey or brown must be 

 equally valuable or valueless for protective purposes in summer. 

 In the short, dark, winter days of the north the importance of 

 any particular shade of colour is problematical, and in any case 

 the white tints would be more advantageous against winged 

 enemies hunting by sight in daylight, than against carnivorous 

 mammals scenting their prey by night. 



During the transition from summer to winter pelage, con- 

 spicuous white patches appear, apparently recapitulating a 

 stage through which the animals passed in the course of their 

 original attainment of the white winter coat. A protective 

 whiteness would surely have been evolved by a general and 

 uniform lightening of the entire pelage ; and it looks as if any pro- 

 tective value which the change may possess is purely incidental. 



The summer pelage is advertising, not protective, directly 

 the animal moves, for then the quite brilliant white under 

 side contrasts sharply with the pigmented upper surface. Even 

 when viewed from behind, the white under parts being then 

 invisible, the glistening upturned tail, 2 and, in the varying 

 hares, the lighter bases of the ears, attract the eye. The 

 suggestion is that the animals are coloured to be conspicuous 

 in motion rather than for invisibility when at rest. 



I cannot find that Mr Abbott H. Thayer's 3 theory of 

 obliteration through countershading is true for hares or for 

 the Rabbit. The white chest, belly, and tail are particularly 

 conspicuous whenever these parts can be seen, which is 

 practically at all times when the animals are not squatting. 

 But they habitually squat when danger threatens, 4 especially 



1 See Proc. Roy. Irish Acad., xxiv., B, 303-314, 1903 ; also F. C. Selous's views 

 in African Nature Notes and Reminiscences, 1908, xiv., n and 41. These ideas are 

 further elaborated in the article on the " Common Stoat." 



2 In the Rabbit the tail is also conspicuous when viewed from the front of the 

 animal, as when it approaches up a hill. Viewed from behind, the black of the 

 upper side sometimes shows up around the white under surface as a dark margin. 



3 Op. cit. supra., p. 223. 



4 When in their forms they constantly jerk their heads up and down, and thus 

 observe anything unusual while at some distance ; they squat on the near approach 

 of a possible enemy. 



