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 contain s 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 (lambda(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 ou ter segment, contains a visual pigment with lambda(max) at approximately 55 1 nm. A relatively rare cone, with a long, slender outer segment, contains an ultraviolet-sensitive visual pigment with lambda(max) at approximately 3 60 nm, All the visual pigments have chromophores based on vitamin A(1). The results are discussed in relation to the behavior of P. regius.