Ovulation releases an egg from an ovarian follicle. The egg is swept into the fallopian tube and begins to descend. Spermatozoa (millions are represented here by one) begin ascending. Fertilization of the egg by a single sperm occurs in the ampullary portion of the fallopian tube about a day after ovulation. The fertilized egg begins to develop into the blastocyt on descent into the endometrial cavity, where implantation occurs on the wall of the fundus about a week after ovulation.