“The same step-ladder which is exhibited by the whole animal kingdom, the steps of which are the different races and classes, with at the one extreme the lowliest animals and at the other the highest, is exhibited also by every higher animal in its development, since from the moment of its origin until it has reached its full development it passes through—both as regards internal and external organisation—the essentials of all the forms which become permanent for a lifetime in the animals lower than itself. The more perfect the animal is, the longer is the series of forms it passes through.” So J. Fr. Meckel wrote in 1812 in his “Handbook of Pathological Anatomy,” _with no thought of descent_. And the facts which led to the construction of the biogenetic law were discovered in no small measure by Agassiz, who was an opponent of the doctrine of descent.(31) But the advance from the doctrine of evolution to that of descent was imperatively prompted by a recognition of the fact that the earth is not from everlasting, and that the forms of life upon it are likewise not from everlasting, that, in fact, their several grades appear in an orderly ascending series. It is therefore simpler and more plausible to suppose that each higher step has arisen from the one before it, than to suppose that each has, so to speak, begun an evolution on its own account. A series of corroborative arguments might be adduced, and there is no doubt, as we have said before, that the transition from the general idea of evolution to that of descent will be fully accomplished. But it is plain that the special idea of descent contributes nothing essentially new on the subject. It is an oft-repeated and self-evident statement, that it is in reality a matter of entire indifference whether man arose from the dust of the earth or from living matter already formed, or, let us say, from one of the higher vertebrates. The question still would be, how much or how little of any of them does he still retain, and how far does he differ from all? Even if there be really descent, the difference may quite as well be so great—for instance, through saltatory development—that man, in spite of physical relationship, might belong to quite a new category far transcending all his ancestors in his intellectual characteristics, in his emotional and moral qualities. There is nothing against the assumption, and there is much to be said in its favour, that the last step from animal to man was such an immense one that it brought with it a freedom and richness of psychical life incomparable with anything that had gone before—as if life here realised itself for the first time in very truth, and made everything that previously had been a mere preliminary play.