Coloured transmission electron micrograph (TEM) showing the peripheral cytoplasm (light brown) of an oocyte, surrounded by the zona pellucida (pink) and follicular cells (blue) of the corona radiata. Mitochondria (red), endoplasmic reticulum (light green), many surrounding vacuoles, and lipid droplets (yellow) can be seen in the oocyte cytoplasm. In the zona pellucida are the short microvilli of the oocyte and the longer and thicker microvilli of the follicular cells (blue).