The process of oogenesis in adult females of Fringilla coelebs was examined by light microscopy, cytochemistry
and autoradiography. Six developmental stages of oocytes are described on the basis of differences in morphology of the nuclear
apparatus. The absence of nucleoli at all the stages of oocyte development is a characteristic feature of this species. Numerous
nucleolus-like bodies connected with lampbrush chromosomes are proved to be protein spheres. These do not contain RNA or
histones and do not incorporate H3-uridine, but they are readily stained with bromphenole blue thus detecting general proteins.
The lampbrush chromosomes are active in RNA synthesis during the oocyte cytoplasmic growth. When vitellogenesis begins, the protein bodies fuse together to form the karyosphere. The spiralizing chromosomes are distributed throughout the surface of the karyosphere. The karyosphere formation is associated with the weakening of RNA synthesis in the oocyte nucleus. On the other hand, RNA synthesis progressively increases in the follicular epithelium.
The location of RNA synthesis in Fringilla oocytes and a probable nutritive function of the follicular epithelium are discussed.