The surface architecture of snake infrared receptor organs

The surface of the epithelium in snake infrared receptor organs is covered with a characteristic array of tiny pores that is different from any other surface structure in squamate reptiles. The measurements and density of the pores differ slightly according to family and species, but the array is characteristic and immediately recognizable. In boids without pits, the array covers the entire surface of each scale that contains infrared receptors, In boids with pits, the array covers the fundus of each receptor pit organ. In crotaline pit organs the array is present on both the outer and inner surfaces of the receptor-containing membrane, and on the epithelium of the wall of the inner chamber. This inner chamber wall is sculpted into a tight array of large and small domed structures, on the surface of which the pore array appears. We speculate that the array of domes in the crotaline pit organ functions as a light trap to prevent infrared rays that penetrate into the inner chamber from being reflected back onto the receptors in the pit membrane. On the other hand, the array of pores, present in all species, appears to reflect away and diffuse visible radiation that might have enough energy to heat-stimulate the receptors and interfere with the target stimulus, i.e., infrared radiation.