13: 438-443. External links Biography and bibliography in the Virtual Laboratory of the Max Planck Institute for the History of Science 1867 births 1941 deaths 20th-century German biologists German embryologists 20th-century German philosophers Parapsychologists People from Bad Kreuznach People from the Rhine Province German male writers University of Freiburg alumni University of Jena alumni People educated at the Gelehrtenschule des Johanneums Gifford Lectures