HAECKEL, hOlel, ERNST (1834—). A Ger man zoologist and natural philosopher, born at Potsdam. He studied medicine and the nat ural sciences at Berlin, under Johannes Midler, and at Jena. After taking his medical degree at Berlin, he practiced medicine for a year, and then, having decided to devote himself to the nat ural sciences, he studied marine life in Heligo land, Messina, and Naples. In 1861 he became privat-docent, in 1862 professor extraordinarius, and in 1865 professor of zoology at Jena. He made numerous scientific journeys, to the Canary Islands, to Norway, the Adriatic, the Red Sea. Corsica, Sardinia, Ceylon, and Java. He pub lished: Die Radiolarien (1862) ; Die Hydromedu sen (1865) ; Enticieklungsgesehichte der Siphono phoren (1869) ; Moneren und andera Protisten (1870) ; Die Kalkschwiimme (1872). The last named work is an important monograph upon calcareous sponges, in which an attempt is made to arrange them in a natural system; the prop osition being that the layers forming the body wall are also homologized with the ectoderm and endoderm of the gastrula. This is the basis laid for the celebrated gastriea theory. Other in vestigations are: Arabischc Korallen (1876) ; Da,s System der Medusen (18SO-S1) ; Reports on the Radiolaria; on the Deep Sea Medusa'; on the Deep Sea Keratosa ; on the Siphonophora Col lected by the Challenger (1882-88); Plankton Studien (1890). Haeckel's philosophical writings were first inspired by Darwin's Origin of Species. In 1866 appeared Die generelle Morphologic der Organism C11, which was the first attempt to apply the general doctrine of development to the whole field of morphology, and also to found a classifi cation'of animals and plants based upon the doc trine of their common relationship. In it he formulates the celebrated 'biogenetic' law, al ready stated by Von Baer, Agassiz, and Fritz Muller. In 1868 appeared Natarliche SchopfungR
gesehichte, translated into English as the His tory of Creation, which is a popular exposition of the doctrine of evolution, and has had the widest circulation and done more to popularize Darwin ism in Germany than any other book. Ueber die Entstehung und den Stammbaum des Men schengeschlechtes ( 1870 ) and Anthropogenie (1874) treat specially of the descent of man. In Die Gastrceatheorie (1874) he traces the phyletic history of all the great groups of the animal kingdom, and finds for all of them a com mon ancestor in the hypothetical gastrna. (See GASTRJEA THEORY.) Haeckel's influence upon con temporaneous thought has been very great. As a popular scientific writer and lecturer he has spread the knowledge of the principles of Dar winism throughout Germany and Europe, while his speculations on the phyletic history and an cestry of the various groups of animals, and his attempts to classify them so as to express their relationships and common descent, although often erroneous, have stimulated investigation and led the way to the correct interpretation of phe nomena. Ile is one of the best-known exponents of the monistic philosophy, which he has ad vocated in most of his speculative writings. His most important contribution to it is Die TV el tratsel. Gemeineerstiindliehe Studien fiber moni stische Philosophic (4th ed. 1900), which has been translated into English as The Riddle of the Universe ( 1902). In 1883 was published a popu larly scientific account of a journey to the East Indies, translated into English under the title of A Visit to Ceylon. The fourth German edition is entitled Insulinde.