The structure of the fetal membranes has been elucidated by the numerous comparative studies of Bautzmann and his colleagues. A complete summary of the literature of normal and pathologic findings in amnion and chorion is found in the monograph of Bourne who, in several studies, has contributed greatly to the understanding of the pathology of the membranes. He distinguishes five distinct layers of the amnion and four of the heavier chorion, considers their embryologic derivation and possible function. Of particular interest in this context is the behavior of the epithelium. Among others, Lange had previously pointed out the presence of intercellular bridges between the epithelial cells of the amnion, observations borne out by electronmicroscopic studies of Bourne & Lacy who also demonstrated the presence of a microvillous surface toward the embryo (Bautzmann, Schmidt & Lemburg). Bautzmann & Hertenstein found no bridges in the amnion of the first trimester of pregnancy (10 cm fetus) but demonstrated their presence at term. At the base of the epithelial cells, these authors were able to demonstrate “feet”; these basal processes were again demonstrated electronmieroscopically by Bourne & Lacy and the complex nature of cell surfaces presumably aids in fluid exchange. In an excellent fine structure study of amnion, Thomas. has provided evidence for a secretory function of this epithelium.