Coloured transmission electron micrograph (TEM) showing the peripheral cytoplasm (light blue) of an oocyte, surrounded by the zona pellucida (pink). In the oocyte cytoplasm, mitochondria are red, endoplasmic reticulum is light green, Golgi apparatus is yellow, and cortical granules dark green. In the zona pellucida are many microvilli of the oocyte (light blue) and one of the follicular cells (purple) contacting with the oocyte surface.