We repeat, then, that in a large number of _genera_, the species cannot be separated by any anatomical characters, and that it is from their history alone naturalists have arrived at those minute divisions now generally received. We may, without the fear of contradiction, go a step further, and assert that several of the races of men are as widely separated in physical organization, physiological and psychological characters, as are the canidæ, equidæ, felines, elephants, bears and others. When the white races of Europe, the Mongols of Asia, the aborigines of America, the black races of Africa and Oceanica are placed beside each other, they are marked by stronger differences than are the species of the genera above named. It has been objected that these gaps are filled by intermediate links which make the chain complete from one extremity to the other. The admission of the fact does not invalidate our position, for we have shown elsewhere (see _Types of Mankind_) _gradation_ is the law of nature. The extreme types, we have proven, have been distinct for more than 5000 years, and no existing causes during that time have transformed one type into another. The well-marked negro type, for example, stands face to face with the white type on the monuments of Egypt; and they differ more from each other than the dog and wolf, ass and _Equis Hemionus_, lion and tiger, &c. The hair and skin, the size and shape of head, the pelvis, the extremities, and other points, separate certain African and Oceanican negroes more widely than the above species. This will not be questioned, whatever difference of opinion may exist with regard to the permanency of these forms. In the language of Prof. Leidy, "the question to be determined is, whether the differences in the races of men are as permanent and of as much value as those which characterize species in the lower genera of animals." These races of men too are governed by the same laws of geographical distribution, as the species of the lower genera; they are found, as far back as history can trace them, as widely separated as possible, and surrounded by local Floræ and Faunæ. VARIETIES.