According to the text, the secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This specific event 'induces the completion of the meiotic division of the secondary oocyte', leading to the formation of a second polar body and a haploid ovum (ootid). This occurs just before the fusion of the haploid nuclei to form the zygote .