Two nuclei in fertilization
In 1875 Hertwig studied fertilization in sea urchin eggs and observed the union of the sperm nucleus with the egg nucleus. This placed an explanation of fertilization on observable cellular structures and supplied material for investigating the nucleus and the contributions of both parents. He later studied egg and sperm formation in Ascaris.
References: [1]
Comparative research with Richard Hertwig
Working with his younger brother Richard, Hertwig investigated the nervous systems and sensory organs of medusae and compared animal germ layers. Their coelom theory of 1881 attempted to explain relationships between animal structures through the formation of body cavities and mesoderm. These studies combined microscopic anatomy with comparisons of development.
References: [1]
Teaching and synthesis in Berlin
Hertwig worked at Berlin’s Second Anatomical Institute from 1888 to 1921. His textbook on the development of humans and vertebrates and Die Zelle und die Gewebe brought together embryology, cytology and histology. The latter work was subsequently revised under the title Allgemeine Biologie.
References: [1]
Radiation as an experimental condition
Between 1909 and 1913 Hertwig investigated the effects of radium radiation on animal reproductive cells and egg development, with contributions from his children Paula and Günther. Such experiments linked altered conditions acting on eggs with observations of fertilization, division and subsequent development.
References: [1]