THE PASSAGE OF SPERMATOZOA THROUGH AND INTO THE ZONA PELLUCIDA OF THE RABBIT EGG

To obtain information about the sperm pathway through the zona pellucida of the rabbit egg, ordinary and phase contrast microscopy were used to study (1) zonae through which spermatozoa had passed, and (2) spermatozoa within zonae. The observations revealed that the spermatozoon makes a narrow slit in the zona as it passes through it. Such slits have a characteristic shape—’ the penetration curve ‘. It is concluded that to pass through the zona, the spermatozoon must follow the penetration curve. Most of the spermatozoa observed within the thickness of the zona apparently started on the curved course and then stopped. They may have stopped within the zona because they were deficient in a substance which normally acts in conditioning the zona to allow spermatozoa to pass through it. Hair-like structures protrude from the front ends of sperm heads into the zona. No definite conclusion has been reached as to whether they are slits in the zona or solid structures ; however, the pictorial evidence favours the interpretation that they are filaments protruding from the sperm heads.