Fig. 4 Building plans of three different types of eyes. aA vertebrate eye.bAn arthopod compound eye.cA cephalopod lens eye. The construction of eyes varies considerably. In vertebrates, photoreceptor cells differentiate from the central nervous system, whereas in cephalopod and arthropod eyes, they differentiate from the epidermis. In addition, the retina is inverse (i.e. photoreceptors are at the back of the eye) in vertebrates and everse (i.e. photoreptors are at the front of the eye) in cephalopods. From Fernald [10]. Close Window