The control of bright colored pigment cells of fishes and amphibians.

SYNOPSIS. The bright colored pigment cells of fishes and amphibians include xanthophores, erythrophores, and iridophores. Their ultrastructure and pigmentary composition are discussed. The role of the hypophysis in controlling both physiological and morphological changes of color in both groups is discussed. The nervous system may be involved in physiological responses of fish iridophores. The physiology of the amphibian iridophore is discussed from the point of view of its parallelism of response to that of the melanophore. Intermedin causes iridophores to contract as do several drugs; the effect of intermedin can be reversed by still other agents. Melatonin has no effect on iridophores. Xanthophores of some fishes and amphibians are induced to expand by intermedin. The morphological effects of intermedin at the organellar level are presented in terms of ultrastructure and pigmentary composition. The integrated response of amphibian dermal chromatophores to intermedin is described as a basic mechanism for change in color.