He was the first chair of both cytology and embryology in Berlin from to and director of the new Anatomical-Biological Institute there. Hertwig initially devoted himself to studying morphological development, a topic on which he wrote a prize essay at Jena in and a doctoral dissertation at Bonn in The two main views in this field at the time were that either the spermatozoa made contact with the egg and stimulated development via the transmission of a subtle mechanical vibration as proposed by Gottlieb-Wilhelm Bischoff , or that the spermatozoa penetrated the egg and mixed their chemical components with the egg yolk.
However, when Auerbach found two nuclei in one egg , he concluded that they must have formed from the mixture of chemical components of the sperm and the egg , not from previous nuclei. Hertwig was dissatisfied with these findings, as he had expected to find a structural continuity between the nucleus of the egg before and after fertilization.
Hertwig knew that his brother Richard was about to join Haeckel on a research opportunity in the Mediterranean, so he quit his assistantship at Bonn to go with them. It was there that he discovered the sea urchin was transparent due to its small size, finely divided yolk , and its lack of a membrane.
Because of this, he was able to observe the spermatozoa as they entered the egg and fused with its nucleus five to ten minutes later. Most importantly, however, Hertwig found that only one spermatozoon was required to fertilize an egg , and that once one spermatozoon entered the egg , the egg formed a vitelline membrane blocking any other spermatozoa from entering. Hertwig submitted his findings as his Habilitationsschrift and was forced to defend his claims against those who believed that the egg cell did not pass through the monera stage in its development.
In fact, Hertwig defended his claim even when the more modern theory of chromosome continuity was proposed. The keys to biological inheritance Hertwig could see the climactic moment of sexual reproduction to such a high level of detail that he also discovered that it is a single sperm that fertilises the egg, although there are many more who try. Thus, when one sperm manages to penetrate an egg, it generates a membrane that prevents the entry of new competing sperm.
Oscar Hertwig continued studying fertilisation inside the ovum and observed that the key was what happened to the chromosomes in this process. In , now a professor of anatomy in Berlin, he was one of the first to teach that the basis of biological inheritance resided in chromosomes. He wrote a textbook that became the reference source on the biological development of animals.
And his great intuition took him one step further, suggesting that within the nucleus there is a chemical substance that is not only responsible for fertilisation, but also for the transmission of hereditary characteristics. Recognised as an eminent scientist, in the final years of his career Oscar Hertwig immersed himself deeply in the theory of evolution and came to the conclusion that Darwin was wrong in his interpretation of evolutionary mechanisms.
Click Enter. Login Profile. Es En. Economy Humanities Science Technology. Multimedia OpenMind books Authors. Featured author. Peter Dicken. Manchester Univertsity, Manchester, UK. Latest book. Work in the Age of Data. Science Leading Figures. Ventana al Conocimiento Knowledge Window. Estimated reading time Time 3 to read. Portrait of Oscar Hertwig made in Credit: Nicola Perscheid After finishing their studies, both brothers abandoned medicine and followed in the footsteps of Haeckel, determined to consolidate and expand the vision of zoology held by their teacher.
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