Eyes and VisionCommon pathways for light detectionPhotopigment molecules and initial chemical pathways are highly conservedMost organisms detect light energies in the range of 400 to 700 nm (visible light)Some have expanded to the ultraviolet range (below 400 nm)Evolution of two types of photoreceptorsCiliary photoreceptors -- large single cilium with highly folded membrane (ex. rods and cones) 相對立體的構造Rhabdomeric photoreceptors -- numerous parallel microvilli 複眼 (ex. arthropod compound eyes)