The Population of Germ Cells in the Developing Female Chick

Abstract

ABSTRACT Morphological and cytological changes occurring in the left (functional) ovary of the developing chick were studied by means of both histological and squash preparations. Counts were made of the numbers of oögonia and oöcytes at various stages of meiotic prophase in specimens aged 9 days’ incubation to 1 day after hatching. Neither the mitotic activity of oögonia nor the onset of the successive stages of meiotic prophase are synchronized throughout the ovary. The development of the germ cells is more advanced at the centre than at the extremities of the ovarian cortex. The process of oögenesis ceases at about the time of hatching. Appreciable numbers of oöcytes enter the pre-leptotene phase on the thirteenth day, zygotene and pachytene on the seventeenth, and diplotene on the nineteenth day of incubation. Degeneration of germ cells occurs throughout the developmental period studied. Oögonial mitoses are associated with an increase in the total population of germ cells from about 28,000 at 9 days’ incubation to some 680,000 on the seventeenth day. Subsequently, a high incidence of degenerating germ cells, together with a decline in the number of oögonial mitoses, account for a decrease in the total population between the seventeenth day of incubation and 1 day after hatching, when only about 480,000 oöcytes persist.