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.

The Hertwig brothers formulated the “coelom” theory to account for the classification and phylogeny of metazoan animals. Digital facsimile from the Internet Archive at this link.

Part 1 was translated as The cell: outlines of general anatomy and physiology, London, 1895.