[The ultrastructure of the rabbit oocyte at the bilaminar follicle stage]

The electron microscope study of the nucleus and organoids of the rabbit oocytes cytoplasm during growth showed nucleoluslike bodies (RNP-granules) on the lampbrushen chromosomes to reach their maximal size at the stage of bilaminar follicle. The RNP-granules differ from the nucleoli by the time of their occurrence cytochemical characteristics, and by their ultrastructural pattern. Throughout the bilaminar follicle stage four components may be seen in the oocyte nucleolus: a dense fibrillar framework around the vacuoles, islets of the granular mass loosely dispersed, and electron dense fibrillar elements filling up the numberous electrontransparant vacuoles. The nucleolus-like bodies are round in shape and have no vacuoles, consisting to two components only: distinctly outlined granules, and weakly developed fibrillar component. The nuclear envelope is seen blebbing. Separation of two nuclear membranes forms a pocket-like enlargements of the perinuclear space. The pockets are limited by small regions between the adjacent nuclear pores. The outer membrane may bulge producing lacuma and large channels in the cytoplasm, which are interconnected making a closed branched network extending inside of the cytoplasm. The nuclear envelope is suggested to be involved in formation of the endoplasmic reticulum through the blebbing process.