The Estonian anatomist and embryologist Karl Ernst von Baer (1792-1876) was the first to describe the mammalian ovum. He also developed the germ-layer theory, which became the basis for modern embryology.

Karl Ernst von Baer was born in Piep on Feb. 29, 1792. He began his medical studies at the University of Dorpat in Estonia in 1810, and after graduating in 1814 he continued his studies at Vienna. After realizing his limitations as a practitioner, he studied comparative anatomy at the University of Würzburg, where he was taught by the influential anatomist Johann Döllinger. On completion of his studies, Baer accepted a position as prosector in anatomy at the University of Königsberg, and in 1819 he was appointed associate professor of zoology there. In 1822 he achieved the rank of professor.

At Königsberg he undertook his famous studies in embryology in collaboration with C. H. Pander...