nearly disappeared, and has been encroached upon and replaced by the old blood of the country, either Macedonian or Thracian. We are ignorant of the laws which govern the disappearance of one race in the sight of another. Sometimes it happens very rapidly; sometimes it does not show itself. The complex conditions which rule it enter into the great order of facts which Darwin has so ingeniously classed under the name of the _struggle for existence_. They have always seemed to us to present a complete analogy with the disappearance of certain animal species before others, the steps of which disappearance history sometimes allows us to measure; so that there seems to be a curious similarity between the great fluctuations of nations and of animals upon continents. We are almost tempted to say that the invasion of the West by the Barbarians, the black rat, and the field mouse, is the triple expression of one and the same biological law. The American population retrogrades, like certain animals;[262] that of the Australian coasts has disappeared; and we believe that the Negroes of Africa themselves will be called, at some distant period, to give up their place in their turn. We do not know any more about the conditions which allow two types to subsist indefinitely one near the other: must we attribute this resistance to the country, or the races which are always before them? Why, if the Normans have disappeared in America, Italy, and Asia, should they still remain in Normandy, few in number, it is true, but always the same, and perfectly described by Linnæus, when he said of the Goths in the Scandinavian peninsula, “They have smooth, fair hair, and the iris of the eye is of a bluish colour.”[263] Even when cross-breedings take place between more than two races,--even when these various influences are mixed together, struggled with, and assisted in a thousand ways, so that the question has become almost inextricable to the anthropologist, in the midst of the varied produce resulting from all these combinations, we are astonished to see here and there individuals who have the absolute and complete character of one of the original stock. Whilst there remains among a people a considerable amount of mixed blood, we may always expect to see some one appear who will have the pure characteristics of the race which was believed to be extinguished, and mingled for ever with the blood of others.[264]