A new type of imaging optics in compound eyes

Many arthropods have compound eyes, made up of numerous separate visual units or ommatidia. In apposition eyes, the ommatidia are optically isolated from each other and provide a poor photon catch because the lenses are so minute1. Much more efficient use of the eye's surface is obtained in superposition eyes, where many ommatidia cooperate to form a superimposed image on the retina1. I report here that, contrary to previous belief2, the eyes of many crabs and hermit-crabs work as superposition eyes by employing imaging optics of a conceptionally new kind. Imaging is accomplished by a remarkable combination of ordinary lenses, cylindrical lenses, parabolic mirrors and light-guides. Despite the impressive complexity of the new mechanism, it is easy to see how this parabolic superposition eye must have evolved from an ordinary apposition compound eye.