HERTWIG, OSCAR (1849-1922), German embryologist, was born on April 21, 1849, at Friedberg. He studied medicine and science in Jena under Haeckel, in Zurich and in Bonn. He was professor at Jena from 1878 until 1888, when he was trans ferred to Berlin, where he died on Oct. 26, 1922. Hertwig was the first to show that fertilization is essentially the fusion of two nuclei—that of the egg and that of the sperm. His other con tributions to biology include his investigation of the foundations of the germ-layer theory, of the parallelism in gametogenesis in the two sexes of Ascaris, and of the malformations of vertebrate embryos callcrl "spina bifida." Hertwig's publications include : Studien zur Blattertheorie (1879-83 ), Die Colomtheorie (1881) and Entwicklung des mitt leren Keimblattes der Wirbelthiere (1883—all three in col laboration with his brother Richard) ; Das Problem der Befrucht wig and der Isotropic des Eies (1884) ; Lehrbuch der Entwick lungsgeschichte des Menschen (1886 ; 9th ed. 191 o ; Eng. trans., 189 2) ; Die Zelle and die Gewebe (2 vols., 1893-98; Eng. trans., 2nd ed., 1909) ; Der Kampf urn Kern f ragen der Entwicklungs und Vererbungslehre (1909; end ed., 192o); Die Elemente der Entwicklungslehre des Menschen and der Wirbeltiere (1900; 4th ed., 191o) ; Die Radiumkrankheit tierzscher Kumzellin (191 1) ; Allgemeine Biologie (5th ed., 192o) ; Das Werden der Organismen (1916) ; Dokumente zur Gesch. des Zeugungslehre (1918), and his edition of the Handbuch der Entwicklungslehre der Wirbel tiere (3 vols., 1901-06) .