Coloured scanning electron micrograph (SEM) of a freeze fracture of embryonic skin from a 14 day old mouse. At top is the epidermis (brown), the outermost layer of skin, which will deepen with development of the embryo. Below this are fibroblasts, cells that produce collagen. Within the fibroblasts are several capillary blood vessels (red). In some cells the nucleus (orange) is visible. Magnification: x1,500 when printed at 15cm wide.