WHITE RABBITS AND WHITE HARES. 13? 



intervening seas or plains, across which they are never 

 reinforced by stray fresh arrivals of solitary individuals. 

 The blue hare thus exhibits on the whole the perma- 

 nence of species under identical conditions, as the red 

 grouse and the willow grouse exhibit the tendency 

 toward variability in species where the conditions have 

 become more or less dissimilar. 



We now know pretty accurately how these little isolat- 

 ed colonies got stranded so far apart from one another 

 on the tops of the hillier regions or in the colder parts 

 of the Eurasiatic continent. During the pleistocene 

 period, before and between the recurrent glacial epochs, 

 the ancestors of the blue hare spread over the whole 

 central plain of Europe, which was then cold enough to 

 suit their peculiar tastes ; and their bones, essentially 

 identical with those of the existing individuals, are 

 found in cave deposits of pleistocene date as far south as 

 the Swabian grottos. At that time they ranged over 

 the chilly lowlands of Belgium, Germany, and the North 

 Sea, in company with the reindeer, the arctic fox, the 

 musk sheep, and the lemming, which have now been 

 driven back "again to the snow-bound regions of the 

 north ; as well as with the Alpine marmot, the chamois, 

 and the ibex, which at present inhabit only the higher 

 ranges of the Alps, the Pyrenees, the Sierra Nevada, or 

 the Caucasus. There they were hunted by the men of 

 the earlier. stone period, who used only weapons of chip- 

 ped flint, unground and unpolished, and who lived for 

 the most part in the limestone caverns now filled in by 

 later accumulations. 



As the climate grew warmer, however, after the 

 clearing away of the ice, the temperate fauna began once 

 more to replace the arctic or sub-arctic kinds in Britain 

 and Germany. The cold period when these northern 



