It is time now to conclude the task, the accomplishment of which has carried me far beyond the limits I had at first proposed to myself. If I have so long detained the reader on the threshold of the edifice, it was to facilitate his after progress, and to give him a chart, that he may not lose himself in the vast field it covers. There he may often meet me again, and if I be sometimes deemed officious with my proffered explanations, he will at least give me credit for good intentions, and he may, if he chooses, pass me without recognition. Both this introduction and notes in the body of the work were thought necessary for several reasons. First, the subject is in some measure a new one, and it was important to guard against misconception, and show, right at the beginning, what was attempted to be proved, and in what manner. Secondly, the author wrote for a European public, and many allusions are made, or positions taken, upon an assumed knowledge of facts, of which the general reader on this side of the ocean can be supposed to have but a slight and vague apprehension. Thirdly, the author has, in many cases, contented himself with abstract reasoning, and therefore is sometimes chargeable with obscureness, on which account familiar illustrations have been supplied. Fourthly, the volume now presented to the reader is one of a series of four, the remainder of which, if this meets the public approbation, may in time appear in an English garb. But it was important to make this, as much as possible, independent of the others and complete in itself. The discussion of the moral and intellectual diversities of the various groups of the human family, is, as I have before shown, totally independent of the question of unity or diversity of species; yet, as it increases the interest attached to the solution of that question, which has been but imperfectly discussed by the author, my esteemed friend, Dr. J. C. Nott, who has so often and so ably treated the subject, has promised to furnish, in notes and an appendix, such additional facts pertaining to his province as a naturalist, as may assist the reader in arriving at a correct opinion.