MAMMALIA. 463 
less of rivers or mountains; and while no obstacle can impede their 
progress, they devastate the country through which they pass. ‘Their usual 
residence appears to be the shores of the Arctic Ocean. ‘Two species of 
this genus are found in North America. 
The lemming of Hudson’s Bay has become the type of the genus Myodes, 
which differs slightly from the genus Lemmus. Its specific name is M. hud- 
sonius. The two middle toes of the fore feet seem to have double claws, 
which is owing to the skin at the end of the toe being callous and projecting 
from under the nail. Of the size of the rat, and lives under the ground. 
The genus /%ber contains but one species, peculiar to North America, 
the musk-rat (/. zibethicus). The lower incisors (two in number as above) 
are sharp-pointed and convex in front; the molars, three on each side, 
above and below, have a flat crown furnished with scaly transverse zigzag 
lamine. ‘The fore feet have four toes with the rudiment of a thumb, and 
the hind feet five, the edge furnished with stiff hairs, which assist the 
animal in swimming, the hind toes semi-palmated. The tail is long, com- 
pressed, granular, nearly naked, having a few scattered hairs. A gland 
near the origin of the tail secretes a white, musky, and somewhat offensive 
fluid. The musk-rats are nocturnal in their habits, consequently their 
manners and customs are difficult to observe. In winter they construct a 
hut on the ice, in which several of them reside together. ‘A pond,” say 
Audubon and Bachman, ‘supplied chiefly, if not entirely, by springs, and 
surrounded by low and marshy ground, is preferred by the musk-rats; they 
seem to be aware that the spring-water it contains probably will not be 
solidly frozen, and there they prepare to pass the winter. Such a place, as 
you may well imagine, cannot, without great difficulty, be approached until 
its boggy and treacherous foundation has been congealed by the hard frost, 
and the water is frozen over; before this time the musk-rats collect coarse 
erasses and mud, with which, together with sticks, twigs, leaves, and any- 
thing in the vicinity that will serve their purpose, they raise their little 
houses from two to four feet above the water, the entrance being always 
from below. We have frequently opened these nests, and found in the 
centre a dry, comfortable bed of grass, sufficiently large to accommodate 
several of them. When the ponds are frozen over, and a slight fall of snow 
covers the ground, these edifices resemble small haycocks. There is another 
peculiarity that, it appears to us, indicates a greater degree of intelligence 
in the musk-rat than we are usually disposed to award to it. The animal 
seems to know that the ice will cover the pond in. winter, and that if it has 
no places to which it can resort to breathe, it will be suffocated. Hence 
you here and there see what are called breathing-places. These are covered 
over with mud on the sides, with some loose grass in the centre, to preserve 
them from being too easily frozen over. We have occasionally seen these 
winter huts of the musk-rat, in the vicinity of their snug summer retreats 
in some neighboring river’s bank, and have sometimes been half inclined 
to suppose that, for some cause or other, they gave a preference to this 
kind of residence. We are not, however, aware that these nests are made 
use of by the musk-rat in spring, for the purpose of rearing its young. We 
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