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Butterfly wing scales. Coloured scanning electron micrograph (SEM) of scales from the topside of a wing of an aega morpho (Morpho aega) butterfly. Layers of wing scales are transparent but tiny ridges on the scales break up and reflect light to give the scales their shimmering iridescent appearance. Magnification: x235 when printed 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/POWER AND SYRED)