Linnaeus, son of a Lutheran pastor, born at Roeshult, in Sweden, in 1707, had barely passed his twenty-fifth year before laying the ground-plan of the system of classification which bears his name, a system which advance in knowledge has since modified. Based on external resemblances, its formulation was possible only to a mind intent on minute and accurate detail, and less observant of general principles. In brief, the work of Linnaeus was constructive, not interpretative. Hence, perhaps, conjoined to the theological ideas then current, the reason why the larger question of the fixity of species entered not into his purview. To him each plant and animal retained the impress of the Creative hand that had shaped it "in the beginning," and, throughout his working life, he departed but slightly from the plan with which he started, namely, "reckoning as many species as issued in pairs" from the Almighty fiat. Not so Buffon, born on his father's estate in Burgundy in the same year as Linnaeus, whom he survived ten years, dying in 1788. His opinions, clashing as they did with orthodox creeds, were given in a tentative, questioning fashion, so that where ecclesiastical censure fell, retreat was easier. As has been seen in his submission to the Sorbonne, he was not of the stuff of which martyrs are made. Perhaps he felt that the ultimate victory of his opinions was sufficiently assured to make self-sacrifice needless. But, under cover of pretence at inquiry, his convictions are clear enough. He was no believer in the permanent stability of species, and noted, as warrant of this, the otherwise unexplained presence of aborted or rudimentary structures. For example, he says, "the pig does not appear to have been formed upon an original, special, and perfect plan, since it is a compound of other animals; it has evidently useless parts, or rather, parts of which it cannot make any use, toes, all the bones of which are perfectly formed, and which, nevertheless, are of no service to it. Nature is far from subjecting herself to final causes in the formation of her creatures." Then, further, as showing his convictions on the non-fixity of species, he says, how many of them, "being perfected or degenerated by the great changes in land and sea, by the favours or disfavours of Nature, by food, by the prolonged influences of climate, contrary or favourable, are no longer what they formerly were." But he writes with an eye on the Sorbonne when, hinting at a possible common ancestor of horse and ass, and of ape and man, he slyly adds that since the Bible teaches the contrary, the thing cannot be. Thus he attacked covertly; by adit, not by direct assault; and to those who read between the lines there was given a key wherewith to unlock the door to the solution of many biological problems. Buffon, consequently, was the most stimulating and suggestive naturalist of the eighteenth century. There comes between him