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 

 worthy of human tools and ingenuity. The fore feet, although 

 small and useless in swimming, are dexterously employed in 

 building, there being considerable 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 the implement 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. 



