Explanation

B to C represents primary and tertiary follicles respectively. Ovary is internally differentiated into four parts, i.e., outer germinal epithelium of cubical cells, a delicate sheath of connective tissue or tunica albuginea, a cortex of dense connective tissue with reticular fibres, spindle-shaped cells, ovarian follicles and a few blood vessels while the central part of medulla is made of less dense connective tissue with elastic fibres, smooth muscles, a number of blood vessels and a few nerves. Maturation of secondary oocyte is completed in mother’s oviduct after the sperm entry into it for fertilization. $2{^\circ}$ oocyte stops advancing further after the completion of metaphase-II. Sperm entry restart the cell cycle by breaking down MPF (Maturation Promoting Factor) and truning on APF (Anaphase Promoting Factor)