The origin and structure of the zona pellucida in the ovarian eggs of teleosts

An exhaustive study of the egg membranes of the oocytes of Trichiurus savala and Triacanthus brevirostris was made with particular reference to the origin and structure of the zona pellucida. The zona pellucida makes its first appearance as a deeply stained narrow zone of fine granular or amorphous homogeneous material around the oocytes, between the follicular epithelium and the vitelline membrane. This homogeneous substance is the product of the follicle cells. Very soon, radial striations in the zona pellucida get formed out of the homogeneous substance of the zona itself. The peripheral cytoplasm of the oocyte, by this time, also gets differentiated into a fibrillar layer. The follicle cells as well as the ooplasmic fibrillar layer send out a number of protoplasmic fibres towards each other into the canalicular passages of the radially striated zona. These fibres meet in the middle of the zona, differentiating it into two concentric zones, an outer—zona radiata externa and an inner-zona radiata interna. The former is purely follicular in origin, whereas the latter is partly follicular and partly ooplasmic in nature.