Dr. Pickering, of the U. S. Exploring Expedition[166]--who does not, however, commit himself to any specific distinctions--has arranged the various races of men on the very simple and obvious ground of color. He obtains in this way four races--the White, the Brown, the Blackish-brown, the Black. The distinction is easy; but it divides races historically, philologically, and structurally alike; and unites those which, on other grounds, would be separated. The white race includes the Hamite Abyssinian, the Semitic Arabian, the Japhetic Greek. The Ethiopian or Berber is separated from the cognate Abyssinian, and the dark Hindoo from the paler races speaking like him tongues allied to the Sanscrit. The Papuan, on the other hand, takes his place with the Hindoo; while the allied Australian must be content to rank with the Negro; and the Hottentot is promoted to a place beside the Malay. It is unnecessary to pursue any farther the arrangement of this painstaking and conscientious inquirer. It conclusively demonstrates that the color of the varieties of the human race must be arbitrary and accidental, and altogether independent of unity or diversity of origin. Some use has been made, by the advocates of diversity of species, of the quality of the hair in the different races. That of the Negro is said to be flat in its cross section--in this respect approaching to wool; that of the European is oval; and that of the Mongolian and American round.[167] The subject has as yet been very imperfectly investigated; but its indications point to no greater variety than that which occurs in many domesticated animals--as, for instance, the hog and sheep. Nay, Dr. Carpenter states[168]--and the writer has satisfied himself of the fact by his own observation--that it does not exceed the differences in the hair from different parts of the body of the same individual. The human hair, like that of mammals in general, consists of three tissues: an outer cortical layer, marked by transverse striae, having in man the aspect of delicate lines, but in many other animals assuming the character of distinct joints or prominent serrations; a layer of elongated, fibrous cells, to which the hair owes most of its tenacity; and an inner cylinder of rounded cells. In the proportionate development of these several parts, in the quantity of coloring matter present, and in the transverse section, the human hair differs very considerably in different parts of the body. It also differs very markedly in individuals of different complexions. Similar but not greater differences obtain in the hair of the scalp in different races; but the flatness of the Negro's hair connects itself inseparably with the oval of the hair of the ordinary European, and this with the round observed in some other races. It generally holds that curled and frizzled hair is flatter than that which is lank and straight; but this is not constant, for I have found