WEISMANN, ALTUST ( 1834—).
A distinguished German zofilogist. He was born January 17. 1834, at Frankfort-on-the-Slain, studied medicine at Gottingen, was clinical as sistant at Rostock in 1856-57, went to Vienna in 1858, to Italy in 1859, and in 1860 to Paris. In 1863 he studied zofilogy as a pupil of Lena art at Giessen. began to lecture at the University of Freiburg in Baden in the same year. and be came in 1866 extraordinary, and in 1871 full pro fessor of zoology. Weismann's epoch-making work on the embryology of the flies appeared in 1864. He first revealed the real nature of the internal changes wrought during the process of meta morphosis of insects. His discovery of the germs of the perfect insect (imaginal buds) in the larva, and his theory of 'histolysis,' or of the complete destruction of the larval organs by a gradual process. led to the final and complete overthrow' of the earlier theory of incasement (enfboirenten I) or preformation (q.v.). These investigations were succeeded by his studies on the formation of the egg and the embryology of the little crustaceans Daphnidre (1876-79), and the origin of the sexual cells of the Hydromedusm (1883). Another and most fruitful line of in vestigation were his researches on the seasonal dimorphism of butterflies, and the origin of the markings of caterpillars, as embodied in his Studies on the Theory of Descent (1S75). As the result of impaired eyesight Weisniano was obliged to abandon microscopic work, and devoted himself to philosophical and speculative studies connected with the theory of descent and the problems of heredity. From being n moderate Lamarekian and seleetionist he went to the ex treme of asserting the "all-sufficiency of natural selection," holding that changes in the physical environment only afford the initial stimulus.
Although .Niger first (1876) proposed the term 'continuity of the germ-plasm,' Weismann greatly expanded the idea, and added many new and original suggestions, establishing the pres ent theory that heredity (q.v.) has a physical basis. Ile was also led to deny what is known
ac use-inheritanee (q.v.), or the Lamarckian doctrine that (diameters acquired during the life time of an animal may be transmitted to its pos terity. Subsequently he proposed a theory of germinal selection. He also valka in ques tion the existence of the influence of a pre vious sire on the progeny of a subsequent one by the same female, giving the name 'telegony' (q.v.) to the phenomenon. Weismann is an admirable investigator. a strong thinker, and the leader of the Neo-Darwinian or Weismannion school of evolutionists. Ilis theories, which are hold. original, and suggestive. have been criticised as superscientific speculations and ass.aimptions, especially that related to the architecture or mechanical arrangement of his hypothetical ele ments or 'determinants' of the germ-plasm (q.v.), but it will be acknowledged by all that he has been a powerful agent in placing mod ern biological studies on a higher plane, and rendering the theory of descent of practical value in psychological and philosophical studies. His principal works are: Die Entwiekelang der DipWen (1864) ; Studien zur Deseendew:theorie (1875-76; Eng. trans., London, 1S82) : Bei /ruff Yaturgeschiehte der Daphnoiden (1876-79) ; Feller die Zahl der Rirhtuu.q.skdrper• and nicer dire Dedeatung auf die (1887) : Essays upon Heredity and Kindred Bio logical Problems (English trans.. Oxford, 1889) ; A Inphinii.ris oder Die der ludi riduen (1891): Aufsiitze fiber 1•cc'crbuac/ (1892) ; The Germ-Plasm, A Theory of Heredity (German, Jena. 1892; English, New York, 1893) ; "The All-Sufliciency of Natural Selection" (Contem porary Review, February, Alarch, and 31ay, 1893) ; The Effect of External Influences upon Development (the Romanes Lecture, 1894) ; Year Gedankea zur Vererbangsfrage. Eine int wort an Herbert Spencer ( 1895) ; Yew Experi ments on the Seasonal Dimorphism of Lepidop tera (English trans., Eatomologist, January-Au gust, 1896) ; Lieber Germinalsclektion (1896) ; Vortrage fiber Deseendenztheorie (1902).