Coloured scanning electron micrograph (SEM) of a freeze fracture of a human foetal membrane, which encloses the foetus in the womb (uterus). At top is the epithelium (pink) the inner layer of the amnion, the inner foetal membrane. Next is the compact layer (brown), which is acellular and formed of reticular fibres made of collagen, followed by the fibroblast layer (yellow), which secretes collagen. The outer layer of the amnion is the extraembryonic coelom, or spongy layer (grey), which is gelatinous and protein-rich. The chorion, the outer foetal membrane includes the cellular (green) and reticular (blue) layers and the trophoblast layer, which facilitates the exchange of nutrients and gases between the mother and foetus. Magnification: x300 when printed at 15cm wide.