Fig. 20. SEM of a stage 2, 4-cell embryo in vitro, (original magnification x1300). The zona pellucida (ZP) has a spongy appearance with one corona radiata cell (C) attached. Arrow points to the hole in the zona pellucida resulting from the intracytoplasmic sperm injection procedure.
(From: Makabe et al., 2001. Reproduced with permission of the Italian Journal of Anatomy and Embryology.)
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