Here, then, we have a whole group of quickwitted tree-monkeys, which, from their structure, we know must have started long ago on a line of their own, wandering down into South America, where they had but few enemies except the boas and pumas and birds of prey, till man came to kill and eat them. And if we wonder how they have gained their quick mischievous intelligence in those quiet pathless forests, we must remember that though a grasping hand and foot seem at first sight of very little importance, yet by means of them the monkey moves rapidly from place to place, swinging, leaping, running, and climbing along the boughs, which are its paths from tree to tree. And since rapid change of any kind makes the eye quick of sight, the ear acute, and the brain active and alive to take in new impressions, it is no wonder that the monkey mind has become alert and ready during the ages that these animals have been chasing and cheating and outwitting each other, or tenderly rearing their young ones among the dangers of the forest. And now if we turn back to the Old World, it is not so much the smaller active tree-monkeys that interest us, for they live much the same life as their American cousins, although they differ from them in never having grasping tails, in having thirty-two teeth like man, in the openings of their nostrils which turn downwards[155] like our own, and in having either cheek-pouches to stow away their food, or stomachs with three compartments like animals that chew the cud, so that they can keep a store within. But in spite of these differences they appear outwardly much the same as the American monkeys; they leap and jump among the trees, and it is not till we come to the Baboons and the tailless man-like apes, that we find ourselves studying quite another kind of life.