Sperm Penetration of the Zona Pellucida of the Pig Egg.

In most mammals that have been studied, the first spermatozoon which penetrates an egg stimulates the egg to undergo a reaction—the 'zona reaction'—which bars further spermatozoa from penetrating through the zona pellucida (Braden, Austin & David, 1954). The sequel to the zona reaction may be classified into two categories, according to species: species in which spermatozoa are entirely prevented from entering the zona, e.g. the hamster, and species in which spermatozoa can penetrate into the zona but cannot traverse it, e.g. the pig. In the present study advantage has been taken of the occurrence of this phenomenon in the pig; spermatozoa in the thickness of the zona were studied, presuming that such observations may furnish clues about the mechanism of sperm penetration of the zona. The structure of the zona was also studied.