Protoplasmic movement during polar-body formation in starfish oocytes

Abstract

The movement of protoplasm during the formation of the polar body in starfish oocytes was analysed by tracing the movements of granules in the cell as index markers, which were recorded by 16 mm cinemicrography. Preparatory to the formation of the polar body, the cell surface expanded at the animal pole and contracted at the vegetal pole, accompanying the movement of endoplasm from the vegetal pole toward the animal pole. With the extrusion of the polar body, the cell surface around the extruded region contracted and the surface at the vegetal pole expanded, accompanying the endoplasmic movement from the animal pole toward the vegetal pole. After extrusion of the polar body, the cell surface at the animal pole expanded, accompanying the endoplasmic movement toward the animal pole in the animal hemisphere. From the movements of the surface and the endoplasm mentioned above and the change in cell shape during polar-body formation, it was concluded that the extrusion of the polar body is caused by the flow of protoplasm into the cell region at the animal pole by internal pressure of the cell through a ring-shaped region of the cortex which actively contracts to form the furrow neck.