Although the eyes of the octopus, and of other cephalopods, and the eyes of vertebrates have evolved entirely independently, each has a retina, a cornea, an iris, a lens, and a fluid-filled interior. These similarities of structure, despite different origins, provide a classic example of biological convergence. However, the cephalopod and vertebrate eyes are also very dissimilar in some respects. For example, the photoreceptor cells in the eye of the octopus point toward the incoming light whereas our own rod cells and cone cells point backward and absorb light reflecting from the back of t…