Are oocytes formed and used sequentially in the mammalian ovary?

Female foetuses normally possess at birth, or soon after birth, their total stock of a million or so oocytes. These oocytes are in dictyotene and await the required hormonal stimulus during adult life for further development leading to ovulation. The situation in the male differs for the spermatogenic cells increase greatly in numbers through mitosis in neonatal and adult life. It is intriguing to know whether there is any regularity in the migration of germ cells into the gonad, in the utilization of oocytes in the adult female or in the mitotic rate of different spermatogenic cells in the testis. Data on differential mitotic rates in spermatogonia are reviewed by Ford in this meeting (see p. 53). Some recent results of Dr S. A. Henderson and myself indicate that there is a considerable degree of order in the formation and use of oocytes in the adult female, their ovulation following a sequence determined somewhere during foetal development (Henderson & Edwards 1968; Fowler & Edwards 1969).