Chin S.H., Gaginskaya E.R., Kalinina E.I.
Peculiarities of oogenesis in the chicken. I. Extrafollicular period in the development of oocytes
Ontogenes (Russ.) — 1979. — V. 10, — P. 340–349.

The early stages of oogenesis in the chick were studied by means of light cytochemistry and autoradiography. The oocytes lack of follicular epithelium are located in the ovarian cortex in groups of 8, 16 or 32 cells. Within the bounds of the group they develop synchronously until the beginning of formation of the follicular epithelium around each oocyte. By 15 days of postembryonic development all oocytes in the ovarian cortex enter the diplotene stage of meiotic prophase. The formation of follicles is completed by 22 days. The morphological descriptions are given for the oocyte nuclei at the preleptotene, leptotene, zygotene, pachytene and early diplotene stages of meiotic prophase. The nucleolus appears at the early diplotene stage and is characterized by extremely weak synthetic activity. It is especially stressed that the nucleolus forms not in all oocytes and that the population of germ cells in the chick ovary is heterogenous by this characteristic. The beginning of RNA synthesis in the oocyte nucleus is timed to the early diplotene .stage. The data are obtained on DNA synthesis in the nuclei of preleptotene and leptotene oocytes not related to the amplification of ribosomal genes.