(d) : The Graafian follicle is fluid­filled capsule that surrounds and protects the developing egg cell inside the ovary during the menstrual cycle. Graafian follicle represents the final stage of follicular development before ovulation. Shortly before ovulation the follicle swells and develops a stigma. At ovulation, the stigma ruptures, releasing the secondary oocyte and corona radiata into the peritoneal cavity to be taken up by the oviduct. The zona granulosa and theca cells remaining in the ovary after ovulation and some surrounding capillaries and connective tissue evolve into the corpus luteum (a temporary endocrine gland) $i.e.$, after the egg cell has been released, the follicle remains and is known as a corpus luteum. The corpus luteum produces progesterone and, in the event of fertilization, provides the required progesterone until the placenta is formed. The corpus luteum also produces some estrogen.