nal form, in internal structure, and in all vital phenomena, so remarkable a mixture or combination of distinguishing animal and vegetable characteristics, that it was impossible, except arbitrarily, to assign them to either realm: he assigned these doubtful beings to a kingdom by themselves, below and yet between the two other organic kingdoms, and this he called protistic. Again and again in existing forms he traced development from preëxisting ones. Many biologists, among them Prof. Huxley, have pronounced this the most important work of the kind ever published."
In the winter of 1867-'68 he delivered a series of popular lectures, on the evolution doctrine in general, which were afterward amplified and published under the title of "The Natural History of Creation." Many editions of it have been called for, and it has been translated into several languages. Darwin says of it, in the introduction to the "Descent of Man:" "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." This work will soon appear in English.
Prof. Haeckel's most important original contribution to the doctrine of evolution has been made by the study of the sponges. Considering that Darwin's mode of investigation was only synthetical, that is, "to prove the truth of the transmutation theory by arguments from philosophy and biology, from comparative anatomy and paleontology, by considerations of the mutual affinities of organic beings, of their embryological relations, their geographical distribution, geological succession, etc." Prof. Haeckel aimed to establish the theory by direct analytical proof. For this purpose "he has selected the group of calcareous sponges, and has shown by thousands of examinations the gradual transitions from the most simple to the most perfect sponge form." Prof. Haeckel's last considerable work is "The History of the Evolution of Man," just ready for issue in Germany, and a very large edition of which has been subscribed for. A translation of this work also will soon appear in English.
We are indebted for the leading facts of this sketch to the excellent notice of Haeckel in Volume VIII. of the American Cyclopædia, where the reader will find a much fuller statement of his numerous contributions to biological science.