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In 1672, Regnier de Graaf first described the differentiation of ovarian follicles into the corpus luteum. He stated that “age and coitus cause very great changes in eggs (follicles). In young animals, they are very small and in more developed ones they are larger. After coitus, they (the follicles) so alter as to resemble the globules (the corpora lutea) …, being one or more according as the animal will produce one or more fetuses.” (1) Follicles as the functional unit: Ovarian follicles have since been shown to be the basic functional unit of the ovary and consist of an outer layer of theca interna cells which encircle inner layers of granulosa cells. Granulosa cells, in turn, surround the innermost oocyte-cumulus cell complex. The maturation of ovarian follicles and their transformation into corpora lutea is regulated by a specific set of hormones and has been a major research area for ovarian physiologists for several hundred years.
Hsueh et al. (Sun,) studied this question.