BEAVER — LODGES. 371 



full development of the newer instinct, is immaterial. 

 Probably, I think, looking to the high antiquity of the 

 building instinct, and also to its being occasionally mani- 

 fested by the Califomian beavers, their case is to be re- 

 garded as one of relapsing instinct. 



In selecting the site of their lodges beavers display 

 much sagacity and forethought. 



The severity of the climate in these high northern latitudes 

 lays upon them the necessity of so locating their lodges as to be 

 assured of water deep enough in their entrances, and also so 

 protected in other respects, as not to freeze to the bottom ; ^ 

 otherwise they would perish with hunger, locked up in ice- 

 bound habitations. To guard against this danger, the dam, 

 also, must be sufficiently stable through the winter to maintain 

 the water at a constant level ; and this level, again, must be so 

 adjusted with reference to the floor of the lodge as to enable 

 them, at all times, to take in their cuttings from without as they 

 are needed for food. When they leave their normal mode of Hfe 

 in the banks of the rivers, and undertake to live in dependence 

 upon artificial ponds of their own formation, they are compelled 

 to prevent the consequences of their acts at the peril of their 

 lives. 



On the upper Missouri, where the banks of the river 

 are for miles together vertical, and rising from three to 

 eight feet above its surface, the beavers resort to the de- 

 vice of making what are called ' beaver slides.' These are 

 narrow inclined planes cut into the banks at intervals, the 

 angle of inclination being 45° to 60°, so as to form a gradual 

 descent from a point a few feet back from the edge of the 

 bank to the level of the river. As Mr. Morgan observes, 

 ' they furnish another conspicuous illustration of the fact 

 that beavers possess a free intelligence, by means of which 

 they are enabled to adapt themselves to the circumstances 

 in which they are placed.' 



Coming now to the habits of these animals in connec- 

 tion with the procuring and storing of food, it is first to 

 be observed that ' the thick bark upon the trunks of large 

 trees, and even upon those of medium size, is unsuitable 



' To obviate this possibility, they often select as their site a place 

 where a spring happens to rise in the bottom of the lake or pond. 



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