Abstract
Mouse eggs obtained from oviducts 14β16 hours after an injection of HCG were inseminated in vitro with fresh epididymal sperm in the presence of heated bovine follicular fluid. When examined one to eight hours later the proportion of sperm without acrosome increased, the proportion of eggs penetrated by sperm increased from 2 to 79%, and that of eggs undergoing fertilization increased from 13% at two hours to 67% at eight hours after insemination. Although the average number of sperm that had penetrated into each egg increased progressively until five hours after insemination, the number of sperm that had entered the vitellus did not increase during this time, showing the existence of a block mechanism in the vitelline membrane. When fresh epididymal sperm were preβincubated in the presence of bovine follicular fluid for three to four hours and used for insemination, sperm penetration occurred 20 minutes later and the proportion of eggs penetrated by sperm increased from 17% at 20 minutes to 90% at two hours after insemination, showing a requirement of capacitation of mouse sperm. When eggs were inseminated with preβincubated sperm, sperm penetration appeared to occur sooner and the proportion of polyspermic eggs was higher in the eggs without follicular cells (17β35%) than in the eggs with follicular cells (3β23%).