Figure 2.

Schematic of generalized photoreceptor cells. (a) Illustration of the arrangement of microvilli along the margin of an arthropod rhabdomeric photoreceptor cell and the previously conceived theoretical random arrangement of the visual pigment chromophore within microvillar membranes, with the double arrow lines representing the dipole axis. The random arrangement of the chromophores would result in a dichroic ratio of 2, which does not fit with current experimental evidence. (b) Illustration of membrane arrangements in ciliary rod and cone photoreceptors comparing the separate flattened discs within rod outer segments with the in-folding of the plasma membrane in cones.