Karl Ernst von Baer's most famous discoveries in anatomy grew out of his work at the University of Königsberg. For more than a century, scientists had attempted to determine the exact nature and location of the mammalian egg. In 1673, Regnier de Graaf had discovered follicles in the ovaries that he thought might be eggs. However, he later found structures even smaller than follicles in the uterus, raising doubts about the role of the follicles themselves. During his research at Königsberg, Baer discovered the mammalian egg by identifying a yellowish spot within the follicle visible only with a microscope. He developed this idea in his 1827 treatise, De ovi mammalium et hominis genesi (On the Origin of the Mammalian and Human Ovum).

Another of Von Baer's accomplishments was his explanation of early embryonic development, a theory that he summarized in his two-volumetextbook Über die Entwicklunggeschichte...