Abstract
The surface of the zona pellucida from unfertilized and fertilized mouse ovawas examined with the scanning electron microscope (SEM) The zona of amature unfertilized ovum showed a sponge-like appearance with numerous fenestrations, Up to 5 hours after fertilization no change was observed in this structure, except for sperm penetration hole which remained almost unchangedeven after cleavage The zona of 2-cell embryo was considerably smoother and aporous appearance was much less obvious. SEM detectable surface change inthe mouse zona pellucida may be due to the precipitates of tubal secretions.
