Ernst Heinrich Haeckel, a German naturalist, born in Potsdam, Feb. 10, 1884. His early predilections were for botanical studies, and while still at the gymnasium he prepared for publication a Flora Merseburgensis. He studied anatomy and histology in Wurzburg under Kolliker and Leydig, and in Berlin under Johannes Muller. Returning to Wurzburg, he became the assistant of Rudolf Virchow. Having studied medicine, he settled in Berlin in 1858 as a practising physician. In 1854 and 1850 he had made with Kolliker and II. Muller scientific excursions to the Mediterranean, some of the results of which he published in 1857 in an essay on the tissues of the river crab. A 15 months' residence in Italy during 1859-'60, which he employed in zoological researches, finally withdrew him from the practice of medicine and made him a professed zoologist. On March 4, 1801, he submitted to the university of Jena his thesis Be Rhizopodum Finibus et Ordinibus; and in1862 he was made extraordinary professor. In the same year he wrote an essay on radiolaria or radiary rhizopods, with an atlas of 35 plates, to which the Cothenius gold medal was awarded.

This work contains not only a complete collection, systematic arrangement, and critical examination of all the genera and species of radiolaria previously observed, but the names, description, and figures of 40 new genera and 144 new species, nearly three times as many as were before known. In this essay Haeckel avowed his conviction "of the mutability of species, and of the actual genealogical relationship of all organisms." Without subscribing to all the views and hypotheses of Darwin as to natural selection, he recognized the great merits of the Darwinian theory, and pointed out its logical consequences. At that time Darwinism was generally looked upon with great disfavor in German scientific circles; and when on Sept. 19, 1863, Haeckel appeared before the convention of German physicians and naturalists held in Stettin as its enthusiastic advocate, he stood almost alone. Thenceforth he determined to devote his life to the extension, establishment, and promulgation of the doctrine of evolution. By continued special investigations he has become an authority among the gatherers of facts in many departments of zoology.

In 1864 he published, with illustrations, " Contributions to the Knowledge of Corycaeide Crustacea," in the Jenaische Zeit-schrift fur Medicin und Naturwissenschaft; and in 1805 an illustrated monograph on gery-onide medusae, which had previously appeared in the same periodical. In the latter year the university of Jena created a regular chair of zoology especially for him, and he began to form by personal collection a museum which has since become one of the most valuable in existence for instruction, and as illustrating points of ontogeny and morphology. From that time his lectures, together with those of Gegenbaur, have made the small university of Jena unrivalled as a school for zoology and comparative anatomy. He has refused very advantageous appointments to other universities, mainly because he would not be separated from his friend and colaborer Gegenbaur. In 1866 he completed a work which, though eclipsed in popularity by two of his later works, the Na-turliche Schopfungsgeschichte and Die Kalk-schwamme, must be considered one of the landmarks of biological science; this is the Gene-relle Morphologie der Organismen (2 vols. 8vo). Its purpose was to trace for anatomy and embryology "immutable natural law in all events and forms." The amount of positive information which this work contains is very remarkable.

We are told in the preface that 20 years previously (that is, when he was only 12 years old) he had two herbariums: "the official one," containing typical forms, all carefully labelled as separate and distinct species; the other a secret one, in which were placed the ' "bad kinds" of rubus, rosa, salix, etc, presenting a long series of individuals transitional from one good species to another. These were at that time the forbidden fruits of knowledge, which in leisure hours were his secret delight. He had later in life greeted Darwin's revival of the transmutation theory with enthusiasm.

Now he could maintain that the boundary lines between different organic forms were not partitions 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 systematic arrangement in the form of genealogical trees. He propounded as a fundamental biogenetic law that "the ontogeny of every organism repeats in brief time and in general outline its phylogeny;" i. e., that the individual development of every organism, or the series of forms through which it passes from germ to completed form, repeats approximately 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, animal and vegetable; but a number of creatures were found to present in external 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 preexisting ones. Many biologists, among them Prof. Huxley, have pronounced this the most important work of the kind ever published. During the winter of 1866 Haeckel made a zoological excursion to the Canary 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 following 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 Schopfungsgeschichte, which has made him known to the German reading public at large. Many editions of this book have been published, and it has been translated into several languages. Darwin says of it in the introduction to his "Descent of Man" (1871): "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." 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," etc, previously published in the Jenaische 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 extended 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 Stammbaum des Men-schengeschlechts (2d ed., 1871); and has written 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 "Annals and Magazine of Natural History," " On the Organization of Sponges and their Rela-tionship to Corals;" this was followed by another 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 explanations, forming vol. iii., 1872). In the investigation and accurate pictorial representation of new genera and species, and the description of the structure and functions of these comparatively unknown members of the animal kingdom, Haeckel has enriched our knowledge 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, analytically, by showing the genealogical connection in a complete group of organisms of the various forms distinguished from each other as species, genera, etc.

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 organic beings, of their embryological relations, their geographical distribution, geological succession, etc. To such considerations Darwin had added the theory of natural selection. Haeckel himself, in his Generelle Morphologie, had applied the synthetical method to organic forms, and popularized it in his Naturliche Schop-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 transitions from the most simple to the most perfect 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 to show that it is originally always a mala species.

In the preface Haeckel says: "Every thinking and candid systematist who has made himself familiar with the natural and artificial systems in the second volume of this monograph will admit that there are here no true species in the dogmatic sense of the schools. Prove to me among the species of calcareous sponges of which numerous individuals have been examined, any bona species in the sense of the schools, and I will give up the whole theory of descent." From this point of view this book, though treating of so special a subject, is of universal interest. With its publication the doctrine of evolution entered upon a new phase. Haeckel's latest work is an essay on "The Gastraea Theory, the Phylogenetic Classification of the Animal Kingdom, and the Homology of the Germ Layers" (1874). The gastrsea theory, to which he was led by his researches on the development of calcareous sponges, is based upon the consideration that all the six higher animal classes, from the sponges to the lowest of the vertebrates, pass through a similar stage of development, which he calls the gastrula stage; it is found that in all of them the original egg cell divides itself by the characteristic process of segmentation or furrowing into at first 2, then 4, then 8, then 10, 32, 64, etc, divisions; and the cellular mass thus formed differentiates itself into two epithelial layers, from the inner one of which the digestive canal with all its appendages is developed, while from the outer layer are formed the skin, nervous system, etc.

From the fact that at one stage of their existence they all essentially consist of a primitive stomach or digestive cavity (whence the name gastrula), and are at that stage more or less alike, and from the homology of the primitive epithelial layers of the germ traceable in all of them, he concludes that they must have been derived from a common original form. This form, essentially corresponding to the developmental stage of gastrula, he proposes to call gastroea, stomach - possessor. The infusoria and still more simple animal organisms have nothing which corresponds to the gastrula stage; and he divides the animal kingdom into the two great groups protozoa, including animal mo-neres, amoeba, and gregarina (which together he calls ovularia), and infusoria; and metazoa, or gastrozoa, the descendants of the gastroea, which include on the one hand the zoophytes or coelenterates, and on the other the worms, with the four higher classes (mollusks, echi-noderms, arthropods, and vertebrates) which have sprung from worms.