Figure 34.17: Rods and Cones (A) This scanning electron micrograph of photoreceptor cells in the retina of a mud puppy (an amphibian) shows cylindrical rods and tapered cones. The cells are artificially colored to distinguish them. (B) The three types of cone cells in the human retina differ in their absorption of the various wavelengths in the spectrum of light, and they therefore differ in their sensitivities to various wavelengths. The dashed line shows the spectral response of rod cells.