Morphogenesis of the secondary envelope of the oocyte in a teleostean fish of the family Cyprinodontidae: Aphyosemion splendopleure

Abstract

The follicular epithelium of the oocyte in Aphyosemion splendopleure is made up of prismatic cells in which the density of the cytoplasm is variable. At the end of vitellogenesis the follicular cells show polarity. The rough endoplasmic reticulum is localized in the cytoplasm situated between the nucleus and the basal lamina. This reticulum splits up into vesicles limited by a membrane covered with ribosomes. At the beginning of postvitellogenesis the Golgi apparatus produces numerous secretion granules in the cytoplasmic region contiguous to the surface of the oocyte. These Golgi elements, together with amorphous material whose origin we have not been able to define, form the secondary envelope of the egg. This envelope is made up of two layers: an inner layer formed by an agglomeration with a membranous aspect and a superficial layer made up of tubular elements. The superficial layer forms an ornamentation clearly shown up by scanning electron microscopy.