These consist of a pair of beavers and their young, and sometimes the young of one or more of these, but the Indians say that it is rare to find more than twelve beavers living together, in the same lodge, because the lodge is not large enough to accommodate more than that number comfortably. From two to five young beavers are born at one time, and when they are two years old, by which time they are almost full-grown, they are not allowed to continue any longer in the parent lodge, but have to go out into the world, to find mates and make lodges for themselves. This, at least, is what the Indians say, and no doubt it must be so, in the greater number of cases. Still as a family of five young beavers, with the two parents, would only make seven in all, and as sometimes more than seven beavers are found living together in one lodge, it seems plain that in these cases some of the young beavers must have stayed in the home circle a little longer, and brought their mates there to live with them. Probably the numbers are in accordance with the size of the interior chamber, for if a beaver felt uncomfortable in his lodge, he would, no doubt, leave it, as we should leave our house or lodgings, but without giving any notice. As I say, the floor of the beaver-house is of mud, but round the outer border of it, next to the wall, the beavers lay down grass, which they use, both to sleep on and also to make nests for their young. The latter are nourished, for six weeks, by their mother, after which, and for the rest of their lives, they live principally on bark. It is not the thick bark, at the base of the trunks of trees, that beavers like, but that which clothes the smaller limbs, for this is both tenderer and more nutritious. This is one great reason for the cutting down of trees, so that the beaver was, no doubt, a tree-feller before he came to be a dam-builder, for food comes first, both with men and animals, and houses and engineering works afterwards.