Surface ultrastructure of preimplantation baboon embryos

Scanning and transmission electron microscopy were used to study baboon preimplantation embryos 3 to 5 days E.F.A. (estimated fertilization age), ranging from about 16 to more than 60 cells. The peripheral blastomers were covered with microvilli scattered on the convex outer surface and along the borders of the intercellular furrows. In younger morulae, some longer microvilli may bridge over the furrow separating contiguous blastomeres. A few blastomeres showed poorly developed microvilli. Blastomeres of smaller diameter than the others may arise from more recent cleavage. Cell junctions as well as small intercellular spaces were noted at the apposition of the blastomere plasma membranes whereas surface intercellular ridges were not observed.