They form separate Families, and are easily recognized as such by the difference in their external outline; but what is the anatomical difference which produces the peculiarity of form in each, by which they have been thus distinguished? It lies in the structure of the limbs, and especially in that of the wrist and fingers. In the Seal the limbs are short, and the wrists are on one continuous line with them, so that it has no power of bending the wrist or the fingers, and the limbs, therefore, act like flappers or oars. The Bear has a well-developed paw with a flexible wrist, but it steps on the whole sole of the foot, from the wrist to the tip of the toe, giving it the heavy tread so characteristic of all the Bears. The Dogs, on the contrary, walk on tip-toe, and their step, though firm, is light, while the greater slenderness and flexibility of their legs add to their nimbleness and swiftness. By a more extensive investigation of the anatomical structure of the limbs in their connection with the whole body, it could easily be shown that the peculiarity of form in these animals is essentially determined by, or at least stands in the closest relation to, the peculiar structure of the wrist and fingers. Take the Family of Owls as distinguished from the Falcons, Kites, etc. Here the difference of form is in the position of the eyes. In the Owl, the sides of the head are prominent and the eye-socket is brought forward. In the Falcons and Kites, on the contrary, the sides of the head are flattened and the eyes are set back. The difference in the appearance of the birds is evident to the most superficial observer; but to call the one Strigidae and the other Falconidae tells us nothing of the anatomical peculiarities on which this difference is founded.