WHITE RABBITS AND WHITE HARES. 145 



Here for the most part the conditions remained so 

 similar that the various animals underwent no material 

 differentiation : though they vary slightly from place to 

 place in the degree to which they retain the habit of 

 turning white in winter. 



In those countries where the snow lies long on the 

 ground they keep up the change of coat as a protection 

 against their enemies, natural selection effectually cutting 

 off any specimen which varies toward brown or black at 

 that season : and here the stoats also for the most part 

 assume the white ermine dress in winter, so as to come 

 upon them unawares. The black tips to the ears doubt- 

 less serve to guide the leverets in following their dams 

 across the snow, without being so conspicuous as to 

 betray the animal to its enemies from a little distance. 

 On the other hand, in northern Siberia, where snow lies 

 almost all the year round, the blue hare has a per- 

 manently white coat ; but in southern Russia it hardly 

 alters in hue, except on the back and sides. 



The Irish hare is regarded by competent authorities 

 as a variety of the blue hare, produced under the ex- 

 ceptionally favourable circumstances of a very warm 

 insular habitat, combined with freedom from competi- 

 tion. In America the closely similar species locally 

 called the rabbit accommodates itself in much the 

 same way to the different zones of climate being white 

 in winter in the north, and yellowish-brown all the year 

 round in the middle and southern States. In this case 

 the two varieties mix so much in the uninterrupted 

 land-surface between the Arctic regions and the Gulf of 

 Mexico that they could not readily grow into distinct 

 species. But in the case of the red grouse of Britain 



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