BEAVER— LODGES. 
371 
full development of the never 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 Californian beavers, their case is to be re- 
garded as one of relapsing instinct. 1 
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 ; 2 * 
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 life 
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 6 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 T feet back from the edge of the 
bank to the level of the river. As Mr. Morgan observes, 
6 they furnish another conspicuous illustration of the fact 
that beavers possess a free intelligence, by means of wffiich 
they are enabled to adapt themselves to the cm um stances 
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 6 the thick bark upon the trunks of large 
trees, and even upon those of medium size, is unsuitable 
1 See also Mental Evolution in Animals , p. 249. 
2 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. 
