HEEEDITY, VARIATION 131 



and the onward march of the survivors never ceases until they reach 

 the sea, into which they plunge, and swimming outwards in the 

 same direction as before, perish in the waves. ... So extraor- 

 dinary was the sudden appearance of these vast bodies of Lem- 

 mings to the Norwegian peasants, that they supposed they must 

 have fallen from tiie clouds. 



" The principal really ascertained facts regarding these migra- 

 tions seem to be as follows : When a combination of favourable 

 circumstances has occasioned a great increase in the numbers of 

 Lenmiings in their ordinary dwelling-places, a movement neces- 

 sarily occurs at the edge of the elevated plateau, and a migration 

 towards the low-lying land begins. The whole body slowly moves 

 forward, advancing in the same general direction in which they 

 started, but following more or less the course of the great valleys. 

 They only travel by night, and they also stay in congenial places 

 for weeks or months, so that, with unaccustomed abundance of 

 food, notwithstanding all the destructive influences to which they 

 are exposed, they multiply excessively during their journey, having 

 families still more numerous and more frequently than in their 

 usual homes. The progress may last from one to three years, ac- 

 cording to the route taken and the distance to be traversed until 

 the sea coast is reached, which, in a country so surrounded by 

 water as the Scandinavian peninsula, must be the ultimate goal of 

 such a Journey. This may be either the Atlantic or the Gulf of 

 Bothnia, according as the migration has commenced from the west 

 or east side of the elevated plateau. Those that finally perish in 

 the sea are only acting under the same blind impulse which has 

 led them previously to cross smaller pieces of water with safety." 



The strange history of these small creatures, besides showing 

 the enormous powers of increase in various types of life, also 

 furnishes us with a fine example of adaptation to what would 

 be, to most animals, extremely adverse conditions — high 

 plateaus within or bordering on the Arctic circle, with its 

 intense cold, its long periods of darkness, buried in snow in 

 winter and with a scantv and stunted vegetation. Yet thev 

 appear to have a most enjoyable existence, and would evidently 

 be able to overrun and occupy a much larger extent of sim- 



