ONE of the founders of the science of heredity and one of Germany's most brilliant embryologists and comparative anatomists, Wilhelm August Oscar Hertwig was born a century ago, on April 21, 1849, in Friedberg, Hessen. A pupil of Schultze, Haeckel and Oegenbaur, he graduated at Bonn in 1872, and in 1881 became professor of anatomy in Jena. Seven years later he was appointed to the chair of general anatomy and embryology at Berlin and to the directorship of the newly created Anatomical-Biological Institute. He served as rector of the University during 1904–5. Retiring in 1921, he died on October 25 of the following year, aged seventy-four. A voluminous and authoritative writer, his works (some in collaboration with his brother Richard) went through many editions and were translated into several languages, for example, his "Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbelthiere". "Die Zelle und die Gewebe" (1893) in the second edition (1906) changed its title to "Allgemeine Biologie", for the author believed that the problems of the living body could be reduced to problems of the single cell. Hertwig was one of the first to teach that the physical basis of heredity must be sought in the chromosomes. His "Cölomtheorie" (1881) helped to complete Balfour's theory of the germinal layers. Perhaps his most important achievements were his discovery in 1875 of the process of fertilization in the sea-urchin, and his observation in 1890 of the first case of parthenogenesis in the animal kingdom-in a starfish. For a number of years he edited the Archiv fur Mikroskopische Anatomie. It is a curious fact that the disciple of Haeckel and Gegenbaur in the end apostatized from Darwinism.