Emil Selenka on the embryonic membranes of the mouse and placentation in gibbons and orangutans

BACKGROUND: Emil Selenka made important contributions to embryology in marsupials, rodents and primates that deserve wider recognition. Here we review his work on early development of the mouse and placentation in the great apes.

FINDINGS: Selenka was intrigued by germ layer theory, which led him to study inversion of the germ layers in the mouse and other rodents. He found it was growth of the ectoplacental cone that caused a downward shift in the position of the underlying ectoderm and endoderm, leading to an inside-outside inversion of these layers. In primates he made the important discovery that the embryos of gibbons and orangutans develop under a decidua capsularis. Thus all great apes, including humans, exhibit interstitial implantation; this is in contrast to other primates where implantation is superficial.

CONCLUSIONS: Selenka's work was thorough and brilliantly illustrated. It was an important influence on his contemporaries and was well known to scientists of the following generation. Embryologists continue to advance our knowledge of fetal membranes and placentation in the mouse, but Selenka's work on gibbons is unique and our knowledge of orangutan placentation is restricted to his specimens.