The Eye

摘要

The eye is an important sense organ of human beings and many animals. For evolutionary reasons, the human eye reacts to the physical stimuli of electromagnetic radiation within a wavelength from 350 to 750 nm. It then converts the stimuli into the perception of light and color. Although the structures of eyes in the animal kingdom are very similar, they have each developed independently of each other, This is clearly seen in the embryonal formation of the eye: while vertebrates eyes develop from a protuberance of the cells that later form the brain, the eyes of mollusks result from an inversion of the outer cell layer that subsequently forms the skin, The most simple "eyes" are photosensitive sensory cells which function as passive optical systems. They can only recognize whether the surroundings are bright or dark (Euglena, Volvox).