Biology of Reproduction, Vol 26, 475-481, Copyright © 1982 by Society for the Study of Reproduction

ARTICLES

Penetration of the mouse sperm head through the zona pellucida in vivo: an electronmicroscope study at 200KV

K Toshimori

The mouse sperm head was examined at the site of fertilization in vivo by 200KV electron microscopy. The spermatozoa penetrating through the zona pellucida had already completed the acrosome reaction and discarded the acrosome. Therefore, the inner acrosomal membrane over- lying the rostral region was directly exposed to surrounding substances. In such spermatozoa, the inner acrosomal membrane was continuous with the outer acrosomal membrane at the posterior boundary of the equatorial segment, while the outer acrosomal membrane was continuous with the plasma membrane at the anterior boundary of the equatorial segment. The equatorial segment, with such a continuity among the membranes, was still intact in the perivitelline space. These morphological characteristics of the mouse sperm head are discussed in relation to the mode of fertilization.

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