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ENTLEMEN: I shall to-day continue the Natural History of Man, which I have undertaken to give you entire. Those of you who were present at our first lecture know that it was devoted to the examination of a fundamental question. We inquired if all the men living upon earth, however they may differ among themselves, are of one and the same species; that is, if they are to be regarded as descended from a single primitive pair.

To answer this question, we appealed to science alone. We started with the principle that, so far as the body is concerned, man is an animal—nothing more, nothing less; that, consequently, all the general laws to which animals are subject bear upon him, and he cannot evade their dominion.

We then asked, not only of animals, but also of plants, What is meant by the word species? and we were led to distinguish species from race.

Without going into the details I then gave, this distinction is easily established. When two individuals of different species unite, the union is almost always infertile, and, if the first union is fertile, the offspring, either immediately or at the end of a few generations, will reproduce no more. So that, between two species, we cannot establish a third series of individuals, starting at first with a father and a mother taken from two distinct species. The examples I gave are known to you all. When we unite a jackass with a mare, an ass with a stallion, we obtain a mule or a hinny, and never a horse or an ass; and, to get mules, it is always necessary to have recourse to a jackass and a mare.

When, on the contrary, we take two individuals of two different races of the same species, whatever their differences of exterior conformation, the resulting individual is fertile, and may give birth to an intermediate series of individuals between the two races.

As examples, I took the different races of dogs, of sheep, of cattle. Whatever the skin, the color, the form, the proportions of the dog, he remains a dog; whatever the proportions, the figure, the color of horses or of oxen, they remain horses and oxen. So, when we cross a water-spaniel with a greyhound, a lap-dog with a Havana dog, the offspring are fertile, and we get what are called fertile mixed races.

Now, when human beings unite with each other, whatever their exterior differences, whether they are white, or black, or yellow, these marriages are fertile. From this fact, verified a thousand times, we