SCANNING ELECTRON MICROSCOPIC STUDY ON THE SURFACE CHANGE OF EGGS OF THE TELEOST, ORYZIAS LATIPES, AT THE TIME OF FERTILIZATION

The surface change of the egg of the teleost, Oryzias latipes , during fertilization was observed with a scanning electron microscope. The microvilli of the outer surface of the unfertilized egg show a slight difference in density between the animal and vegetal pole areas. In the initial step of the breakdown of cortical alveoli (CA), several small holes or gapes are formed at the apical part of the CA membrane, becoming a large aperture from which the alveolar contents are discharged. The formation of microvilli is observed on the inner surface of the exposed cavity left by the CA, starting from the periphery of the aperture and propagating throughout the whole inner surface in accompaniment with the release of the alveolar contents. After the completion of CA breakdown, the CA membrane cannot be distinguished from the original egg plasma membrane.