Europe during the Tertiary period was invaded by successive races of animals driven from their head quarters by press of numbers or by famine, or allured by some modification of circumstances that was specially adapted for their well-being, in precisely the same way as it was subsequently invaded by successive races of men. Eocene Mammals were followed by Miocene, and those again by Pliocene, Pliocene by the Pre-glacial division of the Pleistocene, and, finally, the latter by the Post-glacial or Quaternary, in obedience to the same natural laws which compelled the Stone- to vanish away before the Bronze-folk, and the Kelt to yield to the Teuton. The parallel between the conquest of Europe by the ancient mammalia and that by man is most exact. In both cases the conquering race absorbed a greater or less proportion of the conquered. Thus the Hippopotamus major and Rhinoceros hemitæchus of the Pliocenes of Italy lingered on in France and Germany in association with, or, as it were, in a kind of helotage to, the Post-glacial fauna, just as the Kelt still survives in the midst of his Teutonic conquerors in Britain. In both there is the same uncertainty as to the ancient head-quarters of each race, except the last one, from which the present inhabitants of Western Europe are descended.