ULTRASTRUCTURAL STUDY ON THE ATTACHING FILAMENTS AND VILLI OF THE OOCYTE OF ORYZIAS LATIPES DURING OOGENESIS

The formation of the attaching filaments and villi on the surface of the oocyte of Oryzias latipes were studied electron-microscopically. The oocyte at the early stage has almost smooth surface with a few tufts of microvilli. Some parts of the surface of the oocyte are in contact with the follicle cell, and these parts subsequently become protrusions. As maturation proceeds, a mass of fine granules appears in the space between the protrusion and the follicle cell. Similar granules begin to appear also in the space between the microvilli. These granules later become the outer layer of the chorion. The protrusions are reduced in height, and consequently become almost flat. At the same time, there appears some amorphous material of high electron density on the above-mentioned granules on the flat part. A bundle of parallel microtubules is formed in the material. The tubule is 180–200 A in diameter, and its wall consists of 12 or 13 subunits. The bundle increases in volume, and becomes the attaching filament or villus.