THE TUNDRA AND ITS ANIMAL LIFE. 75 



explains some phenomena of its life which were long considered 

 unintelligible : the almost abrupt occurrence of well-nigh unlimited 

 fertility, and the vast, apparently organized migrations of the 

 animal. In ordinary circumstances the lemming leads a very com- 

 fortable life. Neither in summer nor in winter has he any anxiety 

 about subsistence. In winter he devours all sorts of vegetable 

 matter, moss-tips, lichen, and bark; in summer he lives in his 

 burrow, in winter in a warm, thick - walled, softly - lined nest. 

 Danger indeed threatens from all sides, for not only beasts and 

 birds of prey, but even the reindeer devour hundreds and thousands 

 of lemmings; 10 nevertheless they increase steadily and rapidly, until 

 special circumstances arise when millions, which have come into 

 existence within a few weeks, are annihilated within a few days. 

 Spring sets in early, and a more than usually dry summer prevails 

 in the tundra. All the young of the first litter of the various 

 lemming females thrive, and six weeks later, at the most, these also 

 multiply. Meantime the parents have brought forth a second and 

 a third litter, and these in their turn bring forth young. Within 

 three months the heights and low grounds of the tundra teem with 

 lemmings, just as our fields do with mice under similar circum- 

 stances. Whichever way we turn, we see the busy little creatures, 

 dozens at a single glance, thousands in the course of an hour. They 

 run about on all the paths and roads ; driven to extremity, they 

 turn, snarling and sharpening their teeth, on the defensive even 

 against man, as if their countless numbers lent to each individual 

 a defiant courage. But the countless and still-increasing numbers 

 prove their own destruction. Soon the lean tundra ceases to afford 

 employment enough for their greedy teeth. Famine threatens, per- 

 haps actually sets in. The anxious animals crowd together and 

 begin their march. Hundreds join with hundreds, thousands with 

 other thousands: the troops become swarms, the swarms armies. 

 They travel in a definite direction, at first following old tracks, 

 but soon striking out new ones; in unending files defying all com- 

 putation they hasten onwards; over the cliffs they plunge into 

 the water. Thousands fall victims to want and hunger; the army 

 behind streams on over their corpses ; hundreds of thousands are 



