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', resulting in the formation of a second polar body and a haploid ovum (ootid). The text states that 'Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote'. Therefore, the extrusion of the second polar body occurs after the sperm enters the ovum but before the actual fusion of the nuclei (fertilization) .