Then the Copernican astronomy was finally established through the discoveries of Kepler and Newton, it might well have been pronounced the greatest scientific achievement of the human mind ; but it was still more than that. It was the greatest revolution that had ever been effected in Man's views of his relations to the universe in which he lives, and of which he is — at least during the present life — a part. During the nineteenth century, however, a still greater revolution has been effected. Not only has Lyell enlarged our mental horizon in time as much as Newton enlarged it in space, but it appears that throughout these vast stretches of time and space with which we have been made acquainted there are sundry well-marked changes going on. Certain definite paths of development are being pursued ; and around us on every side we behold worlds, organisms, and societies in divers stages of progress or decline. Still more, as we examine the records of past life upon our globe, and study the mutual relations of the living things that still remain, it appears that the higher forms of life — including Man himself — are the modified descendants of lower forms. Zoölogically speaking, Man can no longer be regarded as a creature apart by himself. We cannot erect an order on purpose to contain him, as Cuvier tried to do ; we cannot even make a separate family for him.