Ultrastructural evolution of nucleoli of female rat germ cells

The nucleoli of oogonia and oocytes of rat ovaries during fetal and neonatal life were studied by light and electron microscopy. An evolution from atypical to typical nucleoli was shown. Nucleoli undergo a gradual increase in size and change from dense fibrillar bodies to complete nucleoli with pars fibrosa, pars granulosa, pars amorpha, and associated chromatin.