the ultrastructure of human spermatozoa located in the cumulus cells and the zona pellucida of a pro-nuclear egg , and in the zona pellucida of a two-cell egg , both fertilized in-vivo , has been analysed in order to understand how the human spermatozoon penetrates the investing coats of the oocyte .
C0043519
zona pellucida
C0029045
oocyte