The photoreceptors and visual pigments in the retina of a boid snake, the ball python (Python regius)

The photoreceptors and visual pigments of Python regius were studied using microspectrophotometry and scanning electron microscopy. The retina contains rods and cones, with rods constituting at least 90 % of the photoreceptor population. The rods are of a single type with long, narrow outer segments and are tightly packed. The wavelength of maximum absorbance (λ_max) of the visual pigment in the rods is in the region of 494 nm. Two distinct types of cone are present. The most common cone, with a stout but stubby outer segment, contains a visual pigment with λ_max at approximately 551 nm. A relatively rare cone, with a long, slender outer segment, contains an ultraviolet-sensitive visual pigment with λ_max at approximately 360 nm. All the visual pigments have chromophores based on vitamin A₁. The results are discussed in relation to the behavior of P. regius.