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Birds, like amphibians, have a third eyelid (the nicitating membrane) that helps them keeps their eyes moistened and allows them to better visualize at high speeds (or, for amphibians, underwater). The glands in birds' eyes allow them to secrete a fluid that is more resistant to evaporation than tears. The membrane also acts as a 'windshield wiper,' with ...


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Birds have a body part known as the nicitating membrane otherwise known as the "third eyelid". This part has become vestigial in humans, where it remains as the plica semilunaris. This image of a masked lapwing clearly shows its nicitating membrane in action, where it covers the eye in a horizontal motion. This is analogous to blinking in humans, and the ...


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The minimum biological light sensor is just an existing signaling molecule that, by chance, also has some change in its activity due to light. There are several ways this could happen. One extremely simple example would be based on a G-protein coupled receptor (GPCR). GPCRs are a family of related signal transduction proteins (the largest family) that sit ...


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A relatively simple proto-eye is the pineal gland. It has been considered to be the third eye and it is involved in circadian rhythms in man, it is involved in thermo regulation, and in reptiles and amfibians it is in fact directly light-sensitive. However, it is not an eye as such, because the pineal does not convey topographical information about the ...


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I think that you are expecting for some complicated system while such things are not necessarily involved. You basically just need a protein that is light-sensitive and some cascade of signal transduction. A light-sensitive protein is just a protein which conformation is changed in the presence of photons of a given wavelength. This cascade of signal ...


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Short answer No. Not two irises are alike, including the irises of identical twins and even the two irises of one and the same person. This uniqueness of the human iris is used in iris scans. The variety of the iris is caused by its complex structure and coloring pattern. Source: Jean-Fran├žois Mainguet Background The iris is explained on Biometric ...



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