The eye is always a closed vesicle, and the internal cornea is extensive.
One result of this among the Vertebrata is that the eyeball is pink in colour, since the cornea, iris and retina being transparent, the red blood contained in the capillaries is unmasked by the absence of pigmentary material.
Early names for it are Lac argenti and Luna cornea, the first referring to its form when freshly precipitated, the latter to its appearance after fusion.
In most cases this cornea is divided into lenticular facets corresponding to the underlying ommatidia.
Light is focused by the cornea and lens at the retina.