Hertwig

HERTWIG, Oscar (Oscar Hertwig, 1849-1922), noted German embryologist and biologist, a student of E. Haeckel; he was professor of anatomy at the University of Berlin. His numerous scientific works (initially together with his brother Richard) relate to the anatomy of invertebrates, cytology, and embryology, in which he was one of the first to apply the experimental method. Subsequently he turned to the development of general biological problems and contributed significantly to the establishment of general biology as an independent discipline. Hertwig was for a long time one of the editors of the journal "Archiv für mikroskopische Anatomie und Entwicklungsgeschichte," which ceased publication after his death. Hertwig's scientific significance is very great; it consists: 1) in the study (together with Richard Hertwig) of the process of fertilization in sea urchins under normal and pathological conditions and in establishing (simultaneously with Strasburger) the importance of the nucleus as the carrier of hereditary properties; 2) in the study of the process of development and maturation of the sexual elements, as a result of which a general scheme of spermatogenesis and oogenesis was established; 3) in works on the germ layers, clarifying the role of the mesoderm and creating the theory of the coelom (Coelomtheorie); 4) in a series of works on experimental embryology, where Hertwig appeared as an opponent of W. Roux's mosaic theory; these works led him to create a general theory of development (biogenesis), which, recognizing the equal heredity of the embryo's cells, takes into account not only internal but also external factors of development; 5) in the criticism of Haeckel's biogenetic law and Darwin's theory. Hertwig's textbooks on embryology and general biology became widely distributed, in which his general views are set forth: "Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbeltiere" (10th ed., Jena, 1915; Russian edition - "Elements of Embryology," St. Petersburg, 1912, and Kharkov, 1928); "Allgemeine Biologie" (5th ed., Jena, 1920; Russian edition - "General Biology," St. Petersburg, 1911); "Das Werden der Organismen" (Jena, 1st edition, 1916; 6th edition, 1920).

HERTWIG, Richard (Richard Hertwig, b. 1850), noted German zoologist. He studied in Jena, Zurich, and Bonn. Hertwig was an honorary professor at the University of Munich, author of the widely used zoology textbook - "Lehrbuch der Zoologie" (14th edition, Jena, 1924) and the book "Abstammungslehre und neuere Biologie" (Jena, 1928), as well as numerous specialized works. Initially, Hertwig, together with his brother Oscar, worked on the morphology of coelenterates, especially jellyfish and sea anemones. Works from this period include: Hertwig O. u. R., "Das Nervensystem und die Sinnesorgane der Medusen" (Lpz., 1878); "Actinien morphologisch und histologisch betrachtet" (Lpz., 1879). Also, together with his brother, Hertwig created in the 1890s the theory of germ layers and the theory of the coelom, which played a very important role in establishing the basic concepts with which a whole generation of embryologists worked. Hertwig worked extensively on protistology, producing a number of major articles and monographs on different groups. For Sarcodina, Hertwig has several articles on rhizopods, a monograph on radiolarians ("Organismus der Radiolarien," Jena, 1879) and a series of works on sexual reproduction and physiological degeneration in Actinosphaerium ("Die Kernteilung bei Actinosphaerium," Jena, 1884). Another group of works is devoted to infusorians; of particular importance is the work "Über Konjugation der Infusorien" (Abhandl. der Bayer. Akad. d. Wiss., 1889), in which the phenomena of maturation in infusorians and multicellular organisms are compared in detail, and the idea of parthenogenesis in infusorians is put forward. Several theoretical articles by Hertwig are based on the aforementioned works; on sexual processes in Protozoa, on the essence of fertilization, on the nucleus and centrosome, etc. On the basis of the same works, Hertwig's teaching of chromidia as a substance passing from the nucleus to the cytoplasm in the form of chromidial networks as "trophic chromatin" arose. This teaching, later developed by Goldschmidt and Hartmann, had for some time great importance in protistology. The study of simple organisms led Hertwig to the idea of the existence of a certain normal ratio between the volume of the nucleus and the cell plasma ("Über Korrelation von Zell- und Kerngrösse und ihre Bedeutung für die geschlechtliche Differenzierung und die Teilung der Zelle," Biol. Centralbl., Vol. XXIII, 1903). This relationship is observed in the resting state of the cell; as for cell division or sexual differentiation of cells, Hertwig considers these phenomena as a result of a violation of the normal ratio, having the aim of again bringing the ratio of the volume of the nucleus and plasma back to normal. The study of the essence of sexual processes led Hertwig to works on sex determination (1904-06); working on the frog, Hertwig tried to clarify the influence of various factors on sex determination, particularly emphasizing the influence of the age of the sex cells participating in the act of fertilization, namely, the influence of overripe sperm, etc.