Fig. 2. Low power TEM of a stage 1b embryo in vitro with a narrow interpronuclear zone, 17 hours post-insemination (original magnification x300). The two pronucle are close to each other in the center of the cytoplasm. They are equal in size and contain dense nucleoli. Cytoplasmic organelles are densely aggregated around the pronuclei. Sperm heads are evident at the surface of the zona pellucida.
(From: Sathananthan and Trounson , 1985. Reproduced with permission of the publisher, John Wiley & Sons)
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