He forms them into a new kingdom of life. To the animal and plant kingdoms he adds the primitive realm of the beings that showed unequivocal signs of the possession of life, yet were neither animals nor plants. He gives them the name of “Protists.” To botany and zoology is now added protistology. The name “protists” (from _protiston_, the very first) is familiar to every one in biology to-day. If protistology has not yet been securely established as a special branch of science, that is due to the circumstance that a strict limit cannot be determined on either the plant or the animal side, so that the botanist encroaches on the province at one point and the zoologist at another. But when we remember that Haeckel’s protists include the well-known bacilli, on which whole libraries are accumulating to-day, it is clear that the province must be definitely marked off at some date in the near future, whether one accepts Darwinism or no. These important innovations in technical biology show very clearly how sound and fruitful the new “natural philosophy” was. We have to go back to the untenable and utterly impracticable systems of Hegel, Schelling, and Steffen, which were immediately rejected as the trifling of _dilettanti_, or even to much that the admirable Oken did on the scientific side, if we would measure the whole distance between what people understood in the sixties by “natural philosophy” and the real reformed philosophy that Haeckel gave to the world. This becomes clearer at every step we take in his work. The first book has determined the method that leads to morphology, the science of forms. The second has ranged the organic forms—protists, plants, and animals—over against the inorganic or “dead” forms, as far as this is possible from the new evolutionary point of view. We feel that the third book will pass on to Darwin, and explain the world of organic forms by the Darwinian laws of evolution. Then the programme would be carried out in its main features. But Haeckel writes two whole books before he comes to this, and they are, perhaps, the most characteristic in the work. He only “adopted” the theory of evolution in the sense that he applied it far more thoroughly than Darwin to practical problems. In these two books he is entirely himself. They are, at the same time, the most difficult in the work. Even to-day they place him on a lofty and lonely height apart from the great and strenuous controversy over Darwinism. I believe that the time will yet come that will fully appreciate these books. Through them Haeckel will play a part in philosophy of which we have at present no prevision.