Such are the absolute rules which have always acted as my guide in anthropological studies. I do not pretend to have invented them. I have scarcely done more than formulate what has been more or less explicitly admitted by Linnæus, Buffon, Lamarck, Blumenbach, Cuvier, the two Geoffroy St.-Hilaire, J. Müller, Humboldt, etc. But, on the one hand, my illustrious predecessors have seldom treated the subject with sufficient precision, and have too often omitted to give the reasons for their decisions. On the other hand these principles have been, and are daily forgotten by men who, in other respects, enjoy with justice the title of great authorities. As I shall be compelled to disagree with them, I thought it necessary to show clearly the general ideas which serve as a foundation for my own scientific convictions. The reader will thus be able to appreciate and discern the causes of this difference of opinion. CHAPTER II. GENERAL ANTHROPOLOGICAL DOCTRINES; MONOGENISM AND POLYGENISM. I. As soon as we have determined the place which should be assigned to man in the great order of the universe, the first question which rises is, whether there is one human species, or several. It is well known that this question has caused a division amongst anthropologists. The _Polygenists_ regard the differences of height, features, and colour, which distinguish the inhabitants of different countries of the globe, as fundamental; the _Monogenists_ consider these differences merely as the result of accidental conditions, which have modified, in various degrees, a primitive type. The former hold that there are _several_ human _species_ perfectly independent of each other; the latter that there is _but one species_ of man which is divided into several races, all of which are derived from a common stock. However slight may be our familiarity with the language of zoology and botany or their applications, it is evident that the question before us is a purely scientific one, and entirely within the province of the natural sciences. Unfortunately the discussion has by no means been confined to this ground.