MORPHOLOGICAL CHANGES OF RABBIT BLASTOCYSTS AT PREIMPLANTATION STAGE / 解剖学报

Ultrastructural changes of the inner cell mass (ICM) in rabbit blastocysts from 4 to 7 days post coitum (p.c.) were observed with transmission electron microscope. It revealed that ICM of blastocyst on day 5 p.c. began to differentiate after they were arranged into a single layer, and under which the primitive endoderm appeared. It is suggested that the primitive endodermal cells in rabbit blastocysts are derived from the scattered ICM-like cells at the inner surface of the mural trophoblast rather than delaminated from ICM proper. In this paper, disruption and disappearance of polar trophoblast are described and discussed.