No part of science became in the succeeding decades so fruitful for Darwinistic purposes as geology. It might very well be called a continuous argument for Darwin; from the little slab of Solenhofen Jurassic schist that yielded, in 1861, the first impression of the archeopteryx, the real connecting link between the lizard and the bird, to the incomparable discoveries of Othniel Marsh, Cope, and Ameghino in America, which put whole sections of the genealogical tree of the mammals before us, on to the skull and thighbone of the ape-man (pithecanthropus) of Java, found by Eugen Dubois, which brings so vividly home to us the transition from the gibbon to man. But, as if it had been scared away by the new idea of evolution and its demand for proof, the most and the best of this material was not forthcoming until after Darwin was pretty firmly established everywhere. At the earlier date we are dealing with it was quite possible for a geologist to play the sceptic with a shadow of justification. We need not go into the point to-day. It is ancient history. But there is an incidental point in Volger’s criticism and the reply it provoked from Haeckel that calls for notice. Volger declared that Darwinism in general was an unsupported hypothesis, but he made a concession. The species of animals and plants need not be absolutely unchangeable. The only thing that is impossible is a continuous upward direction in evolution. All the groups of living things, even the highest, may have been present together from the earliest days. Local changes in the distribution of land and water, &c., must have brought about a certain amount of variation in life-forms. But after brief divergences all would return to the original type. The proper symbol of the story of life is the wave that rises out of the sea and sinks back into it. There was no such thing as a steady advance, a wave that never sank back into the water. The real image of human life is the analogy of its obvious development: youth, maturity, then old age and back once more. The speaker urged in plausible terms that this conception retained the idea of an “eternal becoming,” which is better than a rigid fulfilment. As if an eternally advancing evolution did not include this “eternal becoming.” Haeckel spoke immediately after Volger. He not only attacked the weak points of the geologist, but went on to the deeper philosophic question. The notion of a “perennial circular movement” is “inconsistent with all the facts of human history.” “If we appeal to sentiment, I must say that this circular theory has no attraction for me, whereas the Darwinian idea of a progressive evolution seems the only one consistent with the nature of man.” The story of the animals and plants is subject to “the law of progress” just as much as human history.