372 HAECKEL Now he could maintain that the boundary lines between different organic forms were not par- titions existing in nature, but the expression on our part of the differences which result from divergent development, and which for practical reasons are defined more sharply in our apprehension than the connecting links. He endeavored to bring out the connections and transitions, and to represent them in sys- tematic arrangement in the form of genealogi- cal trees. He propounded as a fundamental biogenetic law that "the ontogeny of every or- ganism repeats in brief time and in general outline its phylogeny;" i. e., that the indi- vidual development of every organism, or the series of forms through which it passes from germ to completed form, repeats approximate- ly the development of its race, or the series of forms through which its ancestors have passed. Moreover, all organic beings hitherto had been classified into the two kingdoms, ani- mal and vegetable; but a number of creatures were found to present in external form, in in- ternal structure, and in all vital phenomena, so remarkable a mixture or combination of dis- tinguishing animal and vegetable characteris- tics, that it was impossible, except arbitrarily, to assign them to either realm; he assigned these doubtful beings to a kingdom by them- selves, below and yet between the two other organic kingdoms, and this he called protistic. Again and again in existing forms he traced de- velopment from preexisting ones. Many biol- ogists, among them Prof. Huxley, have pro- nounced this the most important work of the kind ever published. During the winter of 1866 Haeckel made a zoological excursion to the Ca- nary islands, remaining three months at Are- cife, the harbor town of the island of Lanza- rote. His report of the trip, and of the marine fauna met with, appeared in the Jenaische Zeit- schrift for September, 1867. During the fol- lowing winter he delivered a series of popular lectures on the evolution doctrine in general, and the views of Kant, Lamarck, Goethe, and Darwin in particular, the stenographic report of which constitutes the basis of the Natar- liche Schdpfungsgeschichte, which has made him known to the German reading public at large. Many editions of this book have been pub- lished, and it has been translated into several languages. Darwin says of it in the introduc- tion to his " Descent of Man " (1871) : " If this work had appeared before my essay had been written, I should probably never have com- pleted it. Almost all the conclusions at which I have 'arrived I find confirmed by this natural- ist, whose knowledge on many points is much fuller than mine." His Biologische Studien, erstes Heft: Studien uber Moneren und andere Protisten (1870), is a collection of papers on moneres, " On Catallacts, a new Group of Pro- tists," &c., previously published in the Jenai- sche Zeitschrift. In 1869 a gold medal was awarded him at Utrecht for an essay on the development of siphonophores. He spent the months of August and September of that year on the coast of Norway, and March and April, 1871, on the Dalmatian coast, at Lesina, and in Trieste; while in 1873 he made a more ex- tended excursion in the East. During the last three or four years he has delivered popular scientific lectures at Jena and at Berlin, of which he has published Ueber Arbeitstheilung in Natur- und Menschenleben (1869), Das Leben in den grossten Meerestiefen (1870), and Ueber die Entstehung und den Stamrribaum des Men- schengeschlechts (2d ed., 1871); and has writ- ten on various subjects for periodicals lay and scientific, and a great number of essays. But in September, 1869, appeared an article in the Jenaische Zeitschrift, translated for the " An- nals and Magazine of Natural History," " On the Organization of Sponges and their Rela- tionship to Corals;" this was followed by an- other entitled "Prodromus of a System of the Calcareous Sponges" (an artificial system), and a year later by one " On the Sexual Propagation and the Natural System of Sponges." These articles were the forerunners of the great work on calcareous sponges before mentioned, viz., Die Kalkschwamme : Eine Monographic (2 vols., with an atlas of 60 plates and explana- tions, forming vol. iii., 1872). In the inves- tigation and accurate pictorial representation of new genera and species, and the descrip- tion of the structure and functions of these comparatively unknown members of the ani- mal kingdom, Haeckel has enriched our knowl- edge as much as all previous investigators together; yet this is only an incidental and secondary object of his work. Its aim is to prove the theory of descent in a way that had never before been attempted, namely, analyti- cally, by showing the genealogical connection in a complete group of organisms of the vari- ous forms distinguished from each other as species, genera, &c. What Darwin and all others had attempted was to solve the problem of the origin of species synthetically, i. e., to prove the truth of the transmutation theory by arguments from philosophy and biology, from comparative anatomy and palaeontology, by considerations of the mutual affinities of or- ganic beings, of their embryological relations, their geographical distribution, geological suc- cession, &c. To such considerations Darwin had added the theory of natural selection. Haeckel himself, in his Generelle Morphologic, had ap- plied the synthetical method to organic forms, and popularized it in his Naturliche Schdp- fungsgeschichte. But experience had shown that the synthetical proof alone is not esteemed sufficient by all biologists. Many have asked for analytical proof; and such proof Haeckel has undertaken. He has selected the group of calcareous sponges, and has shown by thousands of examinations the gradual tran- sitions from the most simple to the most per- fect sponge form. This is the first attempt made to follow up the bona species into its last and darkest nook, to bring it to the light, and
