SEM of a stage 2, 4-cell embryo in vitro on post-insemination day 2. Zona pellucida was removed chemically but remnants remain. Blastomeres are in close contact but no flattening has occurred. Microvilli are sparse.
From: Nikas et al., 1996. Reproduced with permission of the publisher, John Wiley & Sons.
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Keywords: blastomere, four-cell embryo, microvilli, stage 2 embryo, zona pellucida
Source: The Virtual Human Embryo.