Oscar Hertwig. Portrait of Oscar Wilhelm August Hertwig (1849-1922), German zoologist and embryologist. Hertwig was a professor at Jena and Berlin Universities and mainly studied the early development of animals. In 1875, whilst observing sea urchin cells, he showed that fertilsation only occurred when a spermatozoa and egg fused. He also showed that only one spermatozoa was required for fertilisation. He also studied the transmission of hereditary characters by cell nuclei and the effect of radioactivity on germ cells.