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Butterfly wing scales. Coloured scanning electron micrograph (SEM) of scales from the wing of an emerald swallowtail (Papilio Palinurus) 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: x530 when printed 10 centimetres wide. The inset at bottom right shows a fracture through a scale. Magnification: x400 when whole image printed at 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE/SCIENCE PHOTO LIBRARY)