Thus we might continue with explanations of terms, but it requires only a few such words and their derivations to make us understand how easy it is, after all, to keep in mind the main families and orders and groups under which all the different animals are classified. And we will soon become so well acquainted with our numerous animal friends in their native homes, and grouped in their proper families, that we can easily recognize many of the animals that must be crowded out of a book of this size. Because we know the meaning of the term used to describe a particular animal, we can place him in the family to which he belongs, and then understand something of his life and habits by comparing them with those of his well-known relatives. [Illustration: FLYING SQUIRRELS.] Quadrumana—The Four-Handed Mammals. WE will begin with the Monkey family in learning about our animal friends, because they resemble mankind more closely than any other animal. Although Darwin and other Naturalists have spent years of their lives in tracing the resemblances between the Human and the Monkey family we had much rather trace the points of difference, for it is not pleasant to claim a very close relationship to some of the hideous monsters who make their homes in the dense forests or distant countries. Although the formation of the body, especially the skull, and the features, are more like ours, than are those of other animals, the first great point of difference is their four hands, those of the legs being formed the same as those of the arm, with thumbs and long flexible fingers, which enables them to climb trees quickly and swing from branch to branch with fearless activity, because they can grasp the limbs of the trees with any one of their four hands. Some of them also use their tails to assist them in climbing, and the Monkeys are sometimes classified under the “prehensile tailed” and the “non-prehensile” tailed according to whether the tails are formed for seizing or grasping the limbs of the trees. And there is still another family of tailless Monkeys. But while many of the different Monkeys are very active in trees, in which they spend the greater part of their time, when in their native homes, this formation of hands instead of feet on their legs, makes them very awkward when standing erect or walking. Even in the most man-like Apes, these hands that serve as feet, are not placed at right angles to the legs, so as to come flat upon the ground like ours; but when the legs are extended, the soles nearly face each other, so that, when erect, the whole weight of the body rests upon the outer edge of the sole of this strange foot, or as it should be more properly called, the palm of the hand. In addition to this peculiarity, the legs are bent inwards to enable them firmly to grasp the boughs of the trees, and this makes them very awkward when trying to walk upright on the ground.