In his "General Morphology," published in 1866, and in his "Natural History of the Creation," the first edition of which appeared in 1868, and finally in his "Anthropogeny"[2] (why he does not say Anthropogony, we are nowhere informed), 1874, this scientist brought the new theory, which had been presented by Darwin in an almost bewildering flood of details, into connection and order, and, analyzing the powers active in natural selection, combined them into an entire system of laws. He {46} at once drew the origin of man also into the course of reasoning on the new theory, and sustained the theory by the discovery of the _monera_ and other low organisms of one cell, as well as by special investigations of the calcareous sponges. For these labors, he was rewarded by the warm and unreserved acknowledgment which Darwin made to him in his work upon the origin of man, which was published subsequently to the "Natural History of the Creation." There Darwin says: "If this work had appeared before my essay had been written, I should probably never have completed it. Almost all the conclusions at which I have arrived, I find confirmed by this naturalist, whose knowledge on many points is much fuller than mine." Haeckel's labors rendered still greater service to the Darwinian theory by dividing the organic world into three kingdoms: the protista kingdom, the vegetable kingdom, and the animal kingdom,--a division which solves in a most simple way the difficulty that was felt more and more of securing for the lowest organisms a place among the animals or plants. He further aided the theory by leaving the choice open to adopt either a uniform or multiform pedigree of the organisms and their kingdoms and classes, and by treating each class under both points of view; and finally, by fascinating experiments to bring before us in detail the hypothetical pedigrees of all classes of organisms from the protista kingdom up to man. We will try to reproduce briefly the pedigree which is of most interest--the hypothetical _pedigree of man_. Haeckel divides it into twenty-two stages, eight of them belonging to the series of the invertebrates, and fourteen to that of the vertebrates. On this ladder of {47} twenty-two rounds, he leads us from the lowest form of the living being, in slight and mostly plausible transitions, continually higher and higher, up to man; and makes our steps easy by mentioning at each stage, on the one hand the corresponding state in the embryonic development, on the other the still living creature through which, in his opinion, the former organisms of the corresponding round of the ladder are still represented, and which accordingly has been a creature that remained on its round, while other members of its family have been developed up to man and to many other genera and species.