MURIDE 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 
