Hertwig, Wilhelm August Oscar (1849–1922)

German zoologist who revealed that fertilization involves the fusion of the nuclei of egg and sperm. He showed for the first time that only one sperm is required to fertilize an egg.

His research was influenced by the work of Haeckel, and described the mechanism of fertilization of sea urchin eggs, work which was of fundamental importance to the development of both the science of embryology and methods of in vitro fertilization over a century later. Auerbach had already demonstrated that a fertilized egg contains two nuclei, but it was Hertwig who discovered that the origins of these nuclei were from the egg and the sperm. He published his results 1875.

Hertwig was born at Friedberg, Hessen, Germany, the son of a chemist who insisted that he be educated at home. He went on to study chemistry and medicine at Jena University and was appointed assistant professor of anatomy there 1878. He was promoted to professor 1881, and finally to the founder chair of cytology and embryology when the position was created 1888.