“The cornea, which in fish is simply a transparent protective cover for the eye, became an image-forming structure in its own right,” wrote the late Michael Land, a biologist at the University of Sussex in England, in a 2005 study in the journal Current Biology, “because it now had air on one side and water on the other.”
Some organisms have kept basic structures—flatworms and mollusks still have their simple pit eyes—while others sprouted mirrored components, elaborate pupil dynamics and arrangements that let their owner see above and below a waterline simultaneously. Even in animals that rely primarily on sensations besides sight, incredible eye features persist.
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