On the Development of the Amnion and Exocœlomic Membrane in the Pre-villous Human Ovum *

An embryologist, as implied by his name, is primarily interested in the development of the embryo as a whole or at least in one or more of its intra-embryonic structures. Being a pathologist, whose interest in embryology has been stimulated by contact with the pathological problems of The Boston Lying-in Hospital, I have, perforce, become more interested in those extra-embryonic structures, the placenta and its associated membranes. It is the purpose of this lecture to discuss the origin and early development of two such extra-embryonic structures, the amnion and the exoccelomic membrane. Due to the fortunate circumstance of having spent a stimulating year as a National Research Fellow with Dr. George L. Streeter (your F-erris Lecturer in 1936), my embryological status might be described as semi-professional. Certainly by no stretch of the imagination would my embryological colleagues consider me a full-fledged professional, and I suspect they probably regard me as a rank amateur. Having thus explained why a combination pathologist and obstetrician has ventured into the anatomical specialty of embryology I now turn to the problem of the amnion and the exoccelomic membrane. If one regards the fertilized ovum, as does Dr. Streeter, from its inception to its death at the end of the Biblical three score and ten years, both these extra-embryonic structures are temptorary, the exoccelomic membrane being far more evanescent than the amnion. The former is present but 4 to 5 days during the pre-villous stage and is the possible precursor of still another temporary structure, the yolk sac. The amnion, by contrast, appears early and persists throughout gestation-a veritable Methuselah as extra-embryonic structures go. Its life span is rivaled only by the chorion, from whose trophoblast it takes origin.