[Electron microscopic study of the development of cortex contractility in the frog oocyte]

The intact and isolated cortices of the Rana temporaria oocytes were studied at different stages of maturation by means of electron microscopy. In the isolated cortex of definitive oocyte the microfilaments were concentrated mainly in the microvilli, whereas under the plasma membrane there was only a thin disordered net of microfilaments. At the stage of the germinal vesicle breakdown and in the ovulated oocyte the microfilaments of isolated cortices formed relatively strong randomly distributed bundles under the plasma membrane. When the oocyte surface was cut through, the microfilaments could form oriented bundles only in cases the oocyte cortex was characterized by distinct contractility.