MURID^E 469 



entirely vegetable, especially grass-roots and stalks, shoots of the 

 dwarf birch, reindeer-lichens, and mosses, in search of which they 

 form, in winter, long galleries through the turf or under the snow. 

 They are restless, courageous, and pugnacious little animals. When 

 suddenly disturbed, instead of trying to escape they will sit upright, 

 with their back against a stone or other coign of vantage, hissing 

 and showing fight in a very determined manner (Fig. 208). 



The circumstance which has given more popular interest to the 

 Lemming than to a host of other species of the same order of 

 animals is that certain districts of the cultivated lands of Norway 

 and Sweden, where in ordinary circumstances they are quite un- 

 known, are occasionally and at very uncertain intervals, varying 

 from five to twenty or more years, literally overrun by an army of 

 these little creatures, which steadily and slowly advance, always in 

 the same direction, and regardless of all obstacles, swimming across 

 streams and even lakes of several miles in breadth, and committing 

 considerable devastation on their line of march by the quantity of 

 food they consume. In their turn they are pursued and harassed 

 by crowds of beasts and birds of prey, as bears, wolves, foxes, dogs, 

 wild cats, stoats, weasels, eagles, hawks, and owls, and never spared 

 by man ; even the domestic animals not usually predaceous, as 

 cattle, goats, and reindeer, are said to join in the destruction, 

 stamping them to the ground with their feet, and even eating their 

 bodies. Numbers also die from diseases apparently produced from 

 overcrowding. None ever return by the course by which they 

 came, and the onward march of the survivors never ceases until they 

 reach the sea, into which they plunge, and swimming onwards in 

 the same direction as before perish in the waves. These extra- 

 ordinary and sudden appearances of vast bodies of Lemmings, and 

 their singular habit of persistently pursuing the same onward course 

 of migration, have given rise to various speculations, from the 

 ancient belief of the Norwegian peasants, shared in by Olaus 

 Magnus, that they fall down from the clouds, to the almost equally 

 untenable hypothesis, ingeniously maintained by the late Mr. W. 

 D. Crotch, that they are acting in these migrations in obedience to 

 an instinct inherited from vastly ancient times, and are still seeking 

 the congenial home in a supposed submerged Atlantis, to which 

 their ancestors of the Miocene period were wont to resort when 

 driven from their ordinary dwelling-places by crowding or scarcity 

 of food. The principal really ascertained facts regarding these 

 migrations seem to be as follows. When any combination of cir- 

 cumstances has occasioned an increase in the numbers of the 

 Lemmings in their ordinary dwelling-places, impelled by the rest- 

 less or migratory instinct possessed in a less developed degree by 

 so many of their congeners, a movement takes place at the edge of 

 the elevated plateau, and a migration towards the lower-lying land 



