Surface of a mouse oocyte This transmission electron micrograph shows the cortex of a mouse oocyte that was undergoing fertilization. The sample was fixed using glutaraldehyde and osmium tetroxide, embedded in plastic, sectioned, and stained with uranyl acetate and lead citrate. Microvilli are present on the oocyte's surface and the zona pellucida is visible surrounding the oocyte. The image was taken with a Phillips 500 transmission electron microscope. The scale bar is 1