HEREDITY, VARIATION 



129 



for wealth, it should have so devastated a whole continent as 

 not to leave room in it for the continued existence of such 

 grand and beautiful life-fomis as the bison and passenger 

 pigeon. 



Equally remarkable, perhaps, is the Norwegian lemming, a 

 little animal somewhat larger than our short-tailed field-mouse, 



Fig. 12. — The Lemming {Myodes lemmus). 



but with a tail only half an inch long. This creature is always 

 abundant in Lapland and northern Scandinavia, but only ex- 

 traordinarily so at long intervals, when favourable conditions 

 lead to its almost incredible multiplication. At intervals of 

 from ten to twenty-five years a great army of them appears, 

 which devours every green thing in its path. Great bands 

 descending from the highlands of Lapland and Finland march 

 in parallel lines about 3 feet apart, never turning aside, cross- 

 ing lakes, and rivers, and even eating through com and hay- 

 stacks when these cross their path. The following recent 



