As man extended his acquaintance with the mammals, he found their number greatly increasing on his hands. Button, like Raleigh, though a professed naturalist, and a writer of admirable genius, had no very distinct notions of species. He was inclined to question whether even the ass might not be merely a degraded horse; and confounded many of the mammals of the New World with their representative congeners in the Old. And yet, in summing up his history of the mammaliferous division, he could state, that though it included descriptions of "a hundred and thirty-four different species of creatures that suckled their young, many of which had not been observed or described before," it was necessarily incomplete, as there were still others to add to the list, for whose history there existed no materials. At the same time he remarked, however, that the "number of quadruped animals whose existence is certain and well established does not amount to more than two hundred on the surface of the known world." Yet here was the extreme estimate made by Raleigh, with what he deemed large allowance for the unknown animals, fairly doubled; and under the hands of more discriminating naturalists, and in the inevitable course of discovery, the number has so enormously increased, that the "eighty-nine distinct species" known to the great voyager have been represented during the last thirty years by the one thousand mammals of Swainson's estimate, the one thousand one hundred and forty-nine mammals of Charles Bonaparte's estimate, the one thousand two hundred and thirty mammals of Winding's estimate, and the one thousand five hundred mammals of Oken's estimate. In the first edition of the admirable "Physical Atlas" of Johnston (published in 1848) there are one thousand six hundred and twenty-six different species of mammals enumerated; and in the second edition (published in 1856), one thousand six hundred and fifty-eight species. And to this very extraordinary advance on the eighty-nine mammals of Raleigh, and the two hundred mammals of Buffon, we must add the six thousand two hundred and sixty-six birds of Lesson, and the six hundred and fifty-seven reptiles of Charles Bonaparte; or at least,--subtracting the sea snakes, and perhaps the turtles, as fitted to live outside the ark,--his six hundred and _forty-two_ reptiles.[29]