[Characteristics of karyosphere formation in the lake frog. Electron microscopic data]

The ultrastructural organization of the karyosphere in oocytes of R. ridibunda during formation of its central body (CB) was examined. It is shown that the material of CB consisting of pores similar to those of the nuclear envelope makes some intimate contact with DNA-containing fibrillar micronucleoli (MN). In the zone of this contact a transfer of MN fibrils into CB is observed. The electron microscope data on the nucleolar origin of numerous MN are provided. It is suggested that MN supply the material for the formation of CB. The participation of r-DNA in this process is discussed.