1849-1922

German zoologist and embryologist who in 1876 postulated that fertilization is a result of the fusion of germ cell nuclei from the male and female parents. This was a departure from the traditional view that the sperm induced a physical vibration or chemical change in the egg that caused it to develop. He observed that only one spermatozoon is required to fertilize the egg, and that after this occurs, additional sperm cells are prevented from entering.