Egg cell. Transmission electron micrograph of an egg cell (red and pink) and its surrounding structures. The egg cell, known as primary oocyte, is formed by a nucleus (red bottom right) and cytoplasm (pink) characterised by the presence of many mitochondria (green). The cytoplasm is surrounded by a thin glycoprotein layer, the zona pellucida (blue and yellow), which is secreted by a stratified epithelium formed by granulosa cells (round and blue centre left). A very thin basal lamina (blue) divides the granulosa cells from the ovarian stroma (green-blue far left). Magnification: x1350 at 6x4.5cm size. Rabbit tissue.