About 12 to 14 days after the start of menstruation, ovulation usually takes place. An ovum matures in one of the ovaries and is released. The ovum moves along the Fallopian tube with the help of the rhythmic contraction of the muscles in its wall and the wave-like motion of the tiny cilia on its walls. If a sperm fuses with this ovum, a zygote forms. If there is no sperm, the ovum dies and disintegrates.