136 RODENTS. 



usually from five to six young in a litter. It is considered by Brehm that there 

 is probably more than one litter in a season ; but precise information as to the 

 breeding-habits of these creatures is still a desideratum. 



It is probable that the periodical migrations of the lemmings are induced by a 

 scarcity of food. Brehm remarks that if an early spring following a wild winter 

 is succeeded by a hot and dry summer, everything will be favourable for an un- 

 wonted increase in the number of these animals. The dry summer will, however, 

 equally tend to diminish the quantity of vegetation available for their support, and, 

 accordingly, a migration to more fertile regions will be rendered necessary. Why, 

 however, the migration should be continued in this extraordinary manner is a 

 question which has not yet received a satisfactgry answer. The number of lem- 

 mings taking part in a migration has been estimated at many millions ; and on 

 such occasions every bush and every rock or large stone has a lemming hiding 

 under it, while sometimes even the towns swarm with these creatures. Not only 

 do the lemmings attempt to swim rivers and lakes which are too wide for them to 

 cross, but, writes Mr. T. T. Somerville, " they tumble into holes, wells, and brooks, 

 the sides of which are too steep for them to scramble out of again, so that frequently 

 people are at a loss to obtain water that is not polluted by their bodies. Doubtless 

 this accounts for an epidemic popularly termed 'lemming fever,' that is said to 

 prevail after the migration, and which is described as resembling ordinary typhoid." 



THE BANDED LEMMING. 

 Genus Cuniculus. 



The banded lemming (Cuniculus torquatus), from the circumpolar regions of 

 both hemispheres, differs in several important points from the true lemmings, and is 

 accordingly referred to a distinct genus. Externally it is distinguished by the 

 absence of conchs to the ear, the shorter and more thickly-formed feet, the practical 

 loss of the first toe of the fore-foot, which has only a rudimental nail, and also by 

 the great length of the claws of the third and fourth toes in the same limb. The 

 molar teeth are more like those of the voles than in the case of the true lemmings, 

 but the first of these teeth in the upper jaw is peculiar in having seven distinct 

 prisms. The banded lemming is so variable in coloration as almost to defy descrip- 

 tion. It may be said, however, in general that the fur of the upper-parts presents 

 a kind of " watered " appearance, owing to the intimate mingling of chestnut, rufous, 

 black, grey, and tawny; the under-parts being leaden-grey. Usually a more or 

 less distinct black line runs along the back from the muzzle to the tail ; while there 

 may be a greyish collar on the nape of the neck. 



The habits of the banded lemming are probably very similar to 

 those of the other species, although it does not undertake similar 

 periodical migrations to the same extent. Baron Nordenskiold states that there 

 are no lemmings in Spitzbergen, but that they must be exceedingly numerous at 

 certain seasons in Novaia Zemlia, where, in early summer, the grass is seen to 

 be traversed in all directions by the tracks made by these animals beneath the 

 snow. 



