Fertilization of rabbit ova and the role of ovum investments in the block to polyspermy.

The rabbit ovum seldom becomes polyspermic despite the presence of supernumerary sperm with easy access to the ovum plasma membrane. The purpose of this study was to characterize the role of ovum investments in blocking polyspermy. Ova were inseminated with capacitated sperm in vitro and were fertilized. Early stages of development were normal. The incidence of polyspermy was determined by cytological examination of fixed ova. The incidence of polyspermy increased following removal of both the zona pellucida and corona radiata but not following removal of only the corona radiata. These results suggest that the failure of supernumerary sperm to penetrate the ovum plasma membrane is at least in part due to the presence of the zona pellucida.