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 evolution, for it is most reasonable to regard the "theme" in every case as a product of common inheritance, while the variations of any theme are best understood as the results of adaptive changes in various directions. But the examples have disclosed a larger relation and a principle of wider scope, as indeed the assignment of all these tribes to the single natural group of the _carnivora_ implies. These tribes are put together because comparative anatomy finds that the common characters of all cats are fundamentally like those of all dogs and bears and seals, and in these common qualities the carnivora differ from all other mammalia. Does this mean that the branches which bear respectively the various members of the several tribes are outgrowths of a single limb of the evolving animal tree? Science does not hesitate to give an affirmative answer, because, as in the case of the similar but varying domestic cats, no other explanation of tribal resemblance in structure seems so reasonable and natural.