I08 THE FOUNDATIONS OF ZOOLOGY 



the migration of our gray squirrels, although the phenomenon has 

 been most carefully studied in the Norwegian lemmings, whose 

 remarkable migrations have figured in literature for centuries. 



The lemming is a small, restless, pugnacious, and very prolific 

 .rodent, somewhat like a guinea pig in shape, which, at uncertain 

 intervals of from five to twenty years, migrates from its ordinary 

 home in the central mountains of Norway and invades the low 

 lands so suddenly and in such numbers that it is still popularly 

 believed to drop from the sky, as in the day of Olaus Magnus, 

 who wrote of it in 1490. 



The great army of lemmings moves on in a straight line and 

 overruns the cultivated country, swimming the lakes and rivers, 

 and causing so much destruction that a special formula to be 

 used against it was authorized by the church, which attempted to 

 check its march by exorcism, as the Bishop of Montreal once 

 tried to exorcise the wild pigeons. The lemmings journey at 

 night, but their march is not continuous, for they make long 

 stops in fertile spots, where they are even more prolific than they 

 were at home, so that they become more and more numerous, 

 although they are attended by bears and wolves, dogs, eagles, 

 hawks, owls, and other birds and beasts of prey, and although 

 even the cattle and reindeer are said to kill and eat them. The 

 march may last for several years, but as they never go back, but 

 continue to move forwards, they at last reach the ocean, and, 

 attempting to swim this, as they have the rivers in their course, 

 all are drowned, like the rats of Hamlin. 



While the migration of the lemmings is undoubtedly due to 

 scarcity, it is difficult to understand its use, for the only ones 

 which profit by it are the ones which have it least developed and 

 stay at home in the mountains, although it may have been useful 

 before the low lands were occupied by man, who now destroys 

 the stragglers and prevents them from scattering and finding per- 

 manent homes. 



While the determining influence is the scarcity of food which 

 comes from crowding, we have no reason to believe that the 

 lemmings consciously and deliberately set out in search of a new 

 feeding ground, or that they have traditions of the rich low lands 

 which attract them as the wealth and luxury of China and Meso- 



