The Thickness and Volume Change of the Zona Pellucida Following Ovulation and Fertilization

ABSTRACT

Since the volume gives a better comparison of size than thickness, the volume of the zona pellucida was also calcldated by substraction of the volume of the inner zonal cavity from the volume of the total egg and compared with the zona pellucida thickness. All calculations were made by computor (CEIR timesharing computor). The zona pellucida of the tubal ova is thicker than that of the oocyte, with the zona pellucida of the fertilized egg being definite1y thinner when compared with unfertilized eggs. This phenomenon of decreased thickness in the fertilized egg may be associated with the zona reaction. The entry of the first sperm into the egg initiates a reaction in the zona pellucida the effect of which is to predude the entry of additional sperm-Braden, Austin and David (1954) defined this phenomenon as the zona reaction. The results of anatomical changes in the zona pe1lucida may also be a phenomenon such as a "zona reaction".