Review lecture: on the organization of reflecting surfaces in some marine animals.

Reflecting surfaces of fish are formed of stacks of thin, flat crystals composed of guanine, as the major component, and hypoxanthine, as the minor component. The broad surfaces of these crystals are not, in general, parallel to the surfaces in which they lie in the fish but they are orientated at angles which depend on the function which they serve. The stacks of crystals in different situations also differ in the number and thickness of crystals and in spectral reflectivity. The organization of these crystals is described, in relation to function, for the silvery surfaces of bony fish, the herring and mackerel, for the reflecting tapeta found in the shark and dogfish, for the photophores of the deep-sea hatchet fish and, finally, for the eye of the scallop.