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MAMMALS OF MINNESOTA. 171 
largest living species, and but few fossil forms could have much 
excelled it, the gigantic Casteroides, elsewhere mentioned, be- 
ing perhaps the largest as it was nearly the size of a black bear. 
A detailed account of the anatomy of the animal is given in 
Capt. Morgan’s work already referred to, to which the reader 
is referred. 
The natural history of the beaver makes a pleasing chapter 
in science both on account of the charming social habits of the © 
animal and the intelligence indicated by his architectural 
powers. The beaver is par excellence the builder among our 
native animals and the forethought evidenced by the dams and 
other structures compels interest. 
With the teeth for ax and chisel and the tail as trowel, the 
beaver is able to perform feats of mechanical engineering 
wortky of human tools and ingenuity. The fore feet, although 
small and useless in swimming, are dexterously employed in 
building, there being considerabie play between the bones of 
the fore arm. The claws are strong and and adapted to bur- 
rowing as the animal is regularly fossorial. The hind feet are 
fully webbed and the claw of the second toe has a curious pro- 
jection below peculiar to this animal. The hearing and smell 
are acute and in part compensate for rather imperfect sight. 
Although social, the social instinct extends but little beyond 
the family circle and is by no means so extended as often 
imagined. 
From two to six young are born after a period of gestation of 
about three or four months. The young are born in May and 
may be weaned in six or eight weeks. 
The food of the beaver consists almost entirely of the bark 
and wood of deciduous trees, birch, cottonwood, willow, poplar 
and maple being preferred. In order to obtain the green 
nutritious bark of the branches, trees of astonishing size, 
considering theimplement used, are cut down and dismembered. 
In preparing for winter great industry is shown. As the 
beaver does not hibernate, he requires suitable food laid away 
for four months of enforced confinement. Like the pocket 
gophers, they are equal to the emergency. Commencing in 
September they cut and store their winter’s food. Though this 
labor is performed chiefly at night, beavers are not strictly 
nocturnal. In regions where they have been unmolested they 
swim freely by day and sun themselves like the mnskrat. 
The location of the burrow and the building of the lodges in- 
dicate great skill, judgment or instinct. 
