Early Human Embryos

Abstract

Rock and Hertig¹ explicitly described their 7·5-day ovum (Mu—8020) as "implanted on" the endometrium; that is, this ovum has only just begun to embed itself and a large part of the ovum is still freely exposed in the uterine cavity. On the other hand, they referred to their older ova (including the 9·5-day ovum, Wi—8004) as "implanted within", "embedded in" the endometrium. In the limits of a short letter, I thus deliberately confined my comparison to "fully implanted" specimens, by which I mean specimens in which no part of the embryonic tissues is exposed freely to the uterine cavity. If completeness of endometrial epithelialization is to be the criterion determining whether an ovum is fully implanted or not, then my specimen is not so far advanced in this respect as the Wi—8004 ovum, in that no surface epithelialization has yet commenced in my specimen, but the embryonic tissues are separated from the uterine cavity by the maternal fibrinous elements of the operculum. This process of epithelialization evidently takes a considerable time, since it is not complete even in the 11·5- and 12·5-day Hertig-Rock ova², by which time the "fully-implanted" ovum has undergone considerable advance in development beyond the stage shown in my specimen.