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 satisfactory 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 deserip- 
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 Nordenskiéld 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. 
Habits. 
