If the menstrual cycle is 29 days long, ovulation takes place on 15th day. Date of ovulation is calculated by substracting 14 days from the duration of menstrual cycle. A surge in LH secretion triggers ovulation, and ovulation normally occurs about 9 hours after the peak of the LH surge at midcycle. The follicle that ruptures at the time of ovulation fills with blood and is called corpus hemorrhagicum. The granulosa and theca cells lining the follicle begin to proliferate and gets filled with yellowish lipid rich luteal cells forming the corpus luteum. Ref: Ganong's Review of Medical Physiology, 24e, chapter 22