Beiträge zur Kenntnis der Bildung, Befruchtung und Theilung des thierischen Eies.

Demonstration that the spermatozoon enters the ovum and that fertilization occurs by the union of the nuclei of the male and female sex cells. Hertwig also established that the transfer of hereditary material is part of the same nuclear process. Hertwig was professor of anatomy at Jena and Berlin.