ith 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.

These few examples, selected purposely among closely allied and
universally known animals, may be sufficient to show, that, beyond the
general complication of the structure which characterizes the Orders,
there is a more limited element in the organization of animals, bearing
chiefly upon their form, which, if it have any general application as
a principle of classification, may well be considered as essentially
characteristic of the Families. There are certainly closely allied
natural groups of animals, belonging to the same Order, but including
many Genera, which differ from each other chiefly in their form, while
that form is determined by peculiarities of structure which do not
influence the general structural complication upon which Orders are
based, or relate to the minor details of structure on which Genera are
founded. I am therefore convinced that form is the criterion by which
Families may be determined. The great facility with which animals may
be combined together in natural groups of this kind without any special
investigation of their structure, a superf