PROGRESS OF THE BACKBONED FAMILY. 749 



bear, and the armadillo, whose back is covered with long shields like 

 the crocodile. 



Having now taken leave of the curious pouch-bearers and the 

 strange primitive sloths and armadillos, we find ourselves left to deal 

 with an immense multitude of modern mammalia, which have spread in 

 endless variety over the earth, and which may be divided into five great 

 groups : the Insectivora, or insect-eaters ; the Rodents, or gnawers ; 

 the climbing and fruit-eating lemurs and monkeys ; the Herblvora, 

 or large vegetable-feeding animals ; and the Carnivora, or flesh- 

 eaters. 



It is clear that the Rodents and Insectivores do not hold their place 

 in the world by strength or audacity. Both lowly groups, of simple 

 structure and with comparatively feeble brains, they have chiefly 

 escaped destruction from higher forms by means of their nocturnal 

 and burrowing habits or arboreal lives, and the marvelous rapidity with 

 which they breed, combined with their power of sleeping without food 

 during; the winter in all cold countries. But the insect-eaters have no 

 water-animal to match the beaver among rodents in sagacity or engi- 

 neering. With his chisel-like front teeth he gnaws a deep notch in 

 the trunk of a larch or pine or willow, and then, going round to the 

 other side, begins work there till the trunk is severed and falls heavily 

 on the side of the deep notch, and therefore away from himself. He 

 always makes the deep notch in the trunk on the side near the water, 

 so that the tree in falling comes as near as possible to the stream. 

 Then, after stripping off the bark and gnawing the trunk into pieces 

 about six feet long, he uses his fore-paws and his teeth to drag them 

 into position to build his dam. He does not always clear away all the 

 branches, but he and his companions place the logs with these lying 

 down the stream, so that they act as supports to resist the current and 

 prevent the dam being washed away. Thus they make a broad foun- 

 dation, sometimes as much as six feet wide, and upon this they pile 

 logs and stones and mud till they have made a barrier often ten feet 

 high and more than a hundred feet long. The lighter branches he 

 uses to make his oven-shaped lodge, laying them down in basket-work 

 shape, plastering them with mud, grass, and moss, and lining the cham- 

 bers with wood-fiber and dry grass. 



There remain to be noticed two groups of much larger animals : 

 first, the Herblvora, or grass-feeders ; and, secondly, their great ene- 

 mies, the Carnivora, or flesh-feeders. We shall see that the vege- 

 table-feeders have filled every spot where they could possibly find a 

 footing, and if we could only trace out their pedigree Ave should be 

 surprised to find how wonderfully each one has become fitted for the 

 special work it has to do. But three things they all require and have. 

 The first of these is a long face and freely-moving under jaw, with 

 large grinding teeth to work up and chew the vegetable food ; the 

 second, a capacious stomach to hold and digest green meat enough to 



