Figure 1.

Retinal photoreceptor complements of colubroid snakes, providing evidence of transmutation as conceived by Walls [2]. Four different morphotypes are illustrated, each showing the different classes of photoreceptors present in the retina of a single species of snake. Arrows indicate the transformation series envisaged by Walls. Photoreceptor images reproduced from Walls [2] with permission from Cranbrook Institute of Science.