German zoologist who specialized in invertebrate research and contributed significantly to the development of parasitology.

Born in a family of biologists, Siebold studied at Berlin and Göttingen and practiced medicine briefly. Largely for his scientific writings, he was made professor of anatomy and physiology at Erlangen; later he held professorial positions at Freiburg, Breslau, and Munich. He founded the Zeitschrift für wissenschaftliche Zoologie (“Journal of Scientific Zoology”), which became one of the foremost periodicals for biological research. Siebold did the work on invertebrates and Friedrich Hermann Stannius did the work on vertebrates, in the book on which they collaborated, Lehrbuch der vergleichenden Anatomie (1846; “Textbook of Comparative Anatomy”), one of the first important texts in comparative anatomy. The book was notable in being based on solid, factual observation and in being a departure from the philosophical presentations common in the earlier years of the century. Siebold also did important work in parasitology; he was one of the first to make practical use of the newly developed idea that the stages in the life cycle of a parasite alternate between its hosts.