Graphic reconstruction of areas of attachment (cross-hatched areas) of stage 4 rhesus embryo #C 610. In these areas the trophoblastic syncytium unites with and dissolves the endometrial epithelium. The epithelial cytoplam disappears first followed by the nuclei later. There is an increase in nuclei at these points. The primordial amniotic cavity is located in the oval area bounded by tthe interrupted line. (From: Heuser and Streeter, 1941)

The numbered lines refer to micrographs of sections shown in Heuser and Streeter (1941). Those figures are also reproduced here (see index).