(a) : The zona granulosa and theca cells of Graafian follicle remaining in the ovary after ovulation and some surrounding capillaries and connective tissue evolve into the corpus luteum (a temporary endocrine gland). The corpus luteum produces progesterone and, in the event of fertilization, provides the required progesterone until the placenta is formed. In the absence of fertilization, the life span of the corpus luteum is 14 days. It then degenerates into a corpus albicans, which is mainly a scar tissue.