It is customary to call spermatozoa “spermatozoa”, while the corresponding eggs are understandably called “ova”. The ovum is the female reproductive cell, produced by the female gonadal ovary, and is about 0.2 mm in diameter. immature eggs are already present in the ovaries of all mammals at birth, and in human beings, the girl’s ovary takes shape at about 3-6 weeks of gestation during the embryonic period. Before birth, millions of oocytes are formed in the ovary, and after “elimination” during childhood and adolescence, only about 100,000 oocytes remain in adulthood. The egg undergoes two “metamorphoses” in its lifetime to change from an immature primary oocyte to a mature egg, which is known medically as “meiosis”. The first “metamorphosis” of the egg, the first meiosis, is quite lengthy, taking place over a period of ten years. The two ovaries of a newborn girl contain a total of about two million primary oocytes, which have entered and stalled in the first meiotic division and are no longer growing. When the girl reaches sexual maturity, the primary oocytes are stimulated by female sex hormones to “wake up” and continue reproducing again. However, instead of these millions of primary oocytes waking up and developing at the same time, one or two (rarely two) primary oocytes continue to develop every 28 days or so from sexual maturity onward. Those oocytes that do not continue to develop gradually die. The primary oocytes “wake up” and grow, during which time the primary oocytes complete their first “metamorphosis” to form secondary oocytes. The “eggs” that are discharged from the ovaries are actually secondary oocytes, or “eggs” as we call them. The secondary oocytes are discharged from the ovaries and are “captured” by the fallopian tubes, where they undergo a second meiotic division. This division takes place after fertilization. Under normal circumstances, one mature egg is produced each month by one side of the ovary, and this process is accompanied by a batch of apoptotic eggs that are precisely and strictly regulated by the hypothalamus-pituitary gland. As a result, a woman ovulates about 400 eggs in her lifetime, and at most 500 eggs, and her oocytes are depleted by the time she reaches menopause. In general, a woman ovulates about 14 days before her next menstrual period. Usually the left and right ovaries take turns ovulating, and in rare cases two or more eggs can be released at the same time. If they are combined with sperm separately, dizygotic twins and multiparous twins occur. The egg matures in a fluid-filled follicle, which we call a “follicle”. At maturity, the follicle can be up to 2 cm in diameter and is one of the largest cells in the body. The average survival time of an egg is 12 to 48 hours after it is expelled from the follicle. During this 48-hour period, the egg is waiting to meet and unite with the sperm. If the egg cannot meet the sperm to form a fertilized egg for a variety of reasons, it will die naturally after 48 to 72 hours. If you lose this chance to be fertilized, you will have to wait for another egg to mature and be expelled a month later, repeating the same process and story. So, how does the egg that is lucky enough to meet with the sperm form a fertilized egg and then conceive a woman? During ovulation, the follicular fluid slowly flows out through the ovulatory orifice with the secondary oocytes of the mound cells. After ovulation, the umbilical end of the fallopian tube is widely dispersed and engorged with blood, and the strength of the contraction of the fallopian tube increases. The egg stays in the abdomen of the fallopian tube, where it meets and fertilizes the sperm, and a new life begins and the egg completes its mission.