Wikipedia:Today's featured article/July 30, 2006
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embryonic development. Some species can rapidly change colour through mechanisms that translocate pigment and reorient reflective plates within chromatophores. This process, often used as a type of camouflage, is called physiological colour change. Cephalopods such as octopuses have complex chromatophore organs controlled by muscles to achieve this, while vertebrates such as chameleons generate a similar effect through cell signaling. Such signals can be hormones or neurotransmitters, and may be initiated by changes in mood, temperature or stress, or by visible changes in the local environment. Unlike cold-blooded animals, mammals and birds have only one class of chromatophore-like cells, the melanocyte. The cold-blooded equivalents, melanophores, are studied by scientists to understand human disease, and are used as a tool in drug discovery. (More...)