In mammals, the intromission of the penis of the male into the vagina of the female, most commonly with some perodic movement of partial withdrawal and re-insertion, which results in the stimulation of the nerves of the penis building to orgasm and ejaculation, during which process a series of muscular contractions delivers semen containing male gametes into the vault of the vagina. The subsequent route of the semen for purposes of fertilization is from the vault of the vagina, through the cervix and into the uterus, and thence into the fallopian tubes. When a fertile ovum or ova from the female is present in the fallopian tubes, the male gamete, usually styled spermatazoa, joins with the ovum resulting in the formation of a new embryo. When a fertilized ovum reaches the uterus, it becomes implanted in the endometrium thereof and a pregnancy begins.
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