This course of classification might have been followed to a much greater extent, for the differences among men are so great that if strict rule is not adhered to it is impossible to fix any limit to species. Unless therefore the principle of unity has been fully conceded at starting, the investigation may result in the admission of a truly indefinite quantity. This is the principle which pervades the writings of the most learned of all the anthropologists of our age, Dr. Pritchard, author of a _Natural History of Man_, which in the original text formed ten volumes, but of which the French language possesses but a very incomplete translation. Dr. Pritchard holds that all people of the earth belong to the same species; he is a partisan of the unity of the human species, but is not satisfied with any of the classifications already proposed, and which were founded upon organic characteristics. He, in fact, entirely alters the aspect of the ordinary classifications which are to be met with in natural history. He commences by pointing out three families, which, he asserts, were in history the first human occupants of the earth: namely, the _Aryan_, _Semitic_, and _Egyptian_. Having described these three families, Pritchard passes to the people who, as he says, radiated in various directions from the regions inhabited by them, and proceeded to occupy the entire globe. This mode of classification, as we have pointed out, leaves the beaten track trodden by other natural historians. For this reason it has not found favor among modern anthropologists, and this disfavor has reacted upon the work itself, which, notwithstanding, is the most complete and exact of all that we possess upon man. Although it has been adopted by no other author, Pritchard’s classification of the human race appears to us to be the most sound in principle. The classification of the human race which we propose to follow, modifying it where in our opinion it may appear to be necessary, is due to a Belgian naturalist, M. d’Omalius d’Halloy. It acknowledges five races of men: the white, black, yellow, brown, and red. When we examine the form and relative size of the brain in ascending the series of mammiferous animals, we find that this organ increases in volume, and progresses, so to say, toward the superior characteristics which it is to display in the human species. The brain increases in importance from the zoophyte to the ape. But, in comparing the brain of the ape with that of man, an important difference becomes at once apparent. The brain of the gorilla, orang-outang, or chimpanzee, which are the apes that bear the greatest resemblance to man, and which for that reason are designated _anthropomorphous_ apes, is very much smaller than that of man.