"The dates, however, of the several passages in question are sufficient to explain the differences in their tenor, in a manner worthy of Buffon. Where are the passages in which Buffon affirms the immutability of species? At the beginning of his work. His first volume on animals[55] is dated 1753. The two following are those in which Buffon still shares the views of Linnaeus; they are dated 1755 and 1756. Of what date are those in which Buffon declares for variability? From 1761 to 1766. And those in which, after having admitted variability and declared in favour of it, he proceeds to limit it? From 1765 to 1778. "The inference is sufficiently simple. Buffon does but correct himself. He does not fluctuate. He goes once for all from one opinion to the other, from what he accepted at starting on the authority of another to what he recognized as true after twenty years of research. If while trying to set himself free from the prevailing notions, he in the first instance went, like all other innovators, somewhat to the opposite extreme, he essays as soon as may be to retrace his steps in some measure, and thenceforward to remain unchanged. "Let the reader cast his eye over the general table of contents wherein Buffon, at the end of his 'Natural History,' gives a _resume_ of all of it that he is anxious to preserve. He passes over alike the passages in which he affirms and those in which he unreservedly denies the immutability of species, and indicates only the doctrine of the permanence of essential features and the variability of details (toutes les touches accessoires); he repeats this eleven years later in his 'Epoques de la Nature'" (published 1778).[56] But I think I can show that the passages which M. Geoffroy brings forward, to prove that Buffon was in the first instance a supporter of invariability, do not bear him out in the deduction he has endeavoured to draw from them. "What author," he asks, "has ever pronounced more decidedly than Buffon in favour of the invariability of species? Where can we find a more decided expression of opinion than the following? "'The different species of animals are separated from one another by a space which Nature cannot overstep.'" On turning, however, to Buffon himself, I find the passage to stand as follows:-- "_Although_ the different species of animals are separated from one another by a space which Nature cannot overstep--_yet some of them approach so nearly to one another in so many respects that there is only room enough left for the getting in of a line of separation between them_,"[57] and on the following page he distinctly encourages the idea of the mutability of species in the following passage:--