diverse as the greyhound and the fox terrier can be crossed. Here again
there are wild forms, like the wolf and fox and jackal, so like the
domesticated members of the dog tribe that we cannot fail to recognize a
common "dog-_ness_" and its significance as evidence of the relationship
in ancestry of all these animals.

Extending our survey so as to include the other tribes of flesh-eaters,
identical principles come to light. One is compelled to regard the polar
and grizzly bears as obvious blood relatives of the brown bear, and even
of the raccoon of our own territory. Instead of walking upon their toes
like cats and dogs, these animals plant their feet flat upon the ground;
and they agree in many other details of structure that place them
together, but somewhat apart from the other tribes. The many kinds of
seals and walruses and sea elephants form still another group displaying
similar bodily characters, but differing more widely from the "cat theme"
in these differences. They are all true carnivora, but in the course of
their evolution they have progressively changed so as to be adapted to
life in the water where they find their prey. The bones of the limbs are
the same in number and arrangement as in the cat's limb, but the seal's
anterior appendage or "arm" has altered in numerous ways so as to become
an efficient flexible paddle, while the hind limbs have shifted
posteriorly, very much as screw propellers have evolved in the history of
steam vessels. How the members of the seal tribe have changed in their
descent from purely terrestrial ancestors is partly explained by such
intermediate animals as the otter. This form is adapted by its slender
body and partly webbed feet to a semi-aquatic life; it seems to have
halted at a point beyond which all of the seals have passed in their
evolution.

Each one of these tribes by itself provides conclusive evidence of