"The number of species here given will appear to many as preposterous. To all such I extend a cordial invitation to visit the National Museum and see for themselves what the bear skulls show. Recognition of species is a matter of interpretation. If the material is adequate there can be little room for difference of opinion; if inadequate, many important points must remain in doubt. It is not the business of the naturalist either to create or to suppress species, but to endeavor to ascertain how many Nature has established, and having discovered this, to point out their characters and learn as much as possible about them. "One of the unlooked-for results of the critical study of the American bears is the discovery that the big bears, like mice and other small mammals, split up into a large number of forms whose ranges in some cases overlap so that three or more species may be found in the same region. "Another surprising result is the discovery that Admiralty Island in Southwestern Alaska appears to be inhabited by no less than five distinct species, each of which is obviously related to and representative of an adjacent mainland species.... "SEXUAL DIFFERENCES "In most species of bears the males are much larger than the females. In some the disparity in size is very remarkable, as in _middendorffi_ of Kodiak Island and _magister_ of southern California. In a few cases the difference is slight, as in _kidderi_ of Alaska Peninsula. "AGE DIFFERENCES "Bear skulls undergo a series of changes from early life to old age, and in most species do not attain their mature form until seven or more years of age. In species having the frontal shield highly elevated, as in _middendorffi_, _kluane_, _stikeenensis_, and _mirabilis_, the frontals reach their maximum of arching or bulging in early adult life (about the sixth year), after which they gradually become flatter.... "CLASSIFICATION OF GRIZZLY AND BIG BROWN BEARS