Structure of Invertebrate Photoreceptors

Abstract

Every explorer is thrilled by the unique and the beautiful. How great must have been the wonder of the first men to view the Grand Canyon of the Colorado, Victoria Falls, Fujiyama on a brilliant winter day, or the planet Earth from outer space. So has it been for me in my explorations of photoreceptors. The last time I conducted a tour of them it was down uncertain and treacherous evolutionary streams (Eakin, 1968). On the present expedition I shall follow a different route and invite the traveler’s attention only to the unique and the beautiful. I hope that he will be impressed with the astounding diversity in nature. Our journey excludes vertebrate photoreceptors. This is fortunate because, from the standpoint of variation in architecture, they are dull and uninteresting. True, there are minor differences between most rods and cones, but all are constructed on the same plan, a stack of disks — even the receptors of the ancient third eye. The pattern is still magnificent, but invertebrate photoreceptors offer a much greater variety.