Scanning microscopy of the early stages of embryonic development of baboons (Papio cynocephalus): oocyte, penetration of the zona pellucida, and morula]

The surface of ovarian oocytes is evenly covered with finger-like microvilli about 1 micron long. Penetration of capcitated spermatozoa in the zona pellucida apparently occurs after acrosome reaction and though a narrow slitmmorulae are constituted of rounded blastomeres, usually of similar size and microvillous covering. A few blastomeres may be smaller than others, probably as a result of faster mitotic rate in one of the blastomeres compared to adjacent ones. Microvilli are numerous in the interblastomeric furrows where junctional ridges are not observed at the 30-40 cell stage.