A comparative investigation of the oocyte nuclear apparatus in 9 species of birds has shown that in adult ovaries all
the oocytes are at the diplotene stage of meiosis (a vegetative phase of oogenesis) and lack true nucleoli. The oocytes in the small
growth period (early diplotene) contain spiralized chromosomes being in a relative resting state. Such oocytes constitute a sexcell
storage from which mature eggs develop every year.
As the period of big growth begins, the chromosomes transform into typical lampbrush chromosomes. Like the situation in other vertebrates, in bird oocytes the lampbrush stage lasts not less than one year. Being the stage of the synthetic activity of the oocyte nucleus, it coincides in time with the period of oocyte cytoplasm growth. At the end of cytoplasmicthe beginning of trophoplasmic oocyte growth, the chromosomes lose their lateral loops, but no chromosome coiling can be revealed by Feulgen technique at that time. A similar detaching of lateral loops from chromosomes after the stopping of lampbrush chromosome functioning is discussed.