Pseudo-Melanosis in the Tail of Trout and Salmon

Abstract

HE nature of the control of the movements of the granules in pigment cells of lower vertebrates has received considerable attention among biologists for a great number of years. Numerous investigators have supported the theory of a double innervation of the chromatophores, one system of nerves (parasympathetic) controlling the expansion, another (sympathetic) controlling the contraction of the pigment cells. Among the first to bring forth this view was Bert (1875), as a result of his investigations on the chameleon. Later, Carnot (1897) drew similar conclusions in regard to the amphibian chromatophores, basing his belief upon what he considered the separation by certain drugs of the action) of two types of nerves which he called chromatodilators and chromatoconstrictors. Sollaud (1908) claims to have seen nerve fibers in actual connection with the chromatophores of the frog. However, Hogben (1924) and his collaborators have definitely shown that the pituitary secretion is the main factor in regulating the chromatic function in amphibia. He also believes that possibly adrenal secretion or some auxiliary mechanism plays a subsidiary part, but there are no satisfactory grounds for believing that nervous agencies directly influence amphibian melanophores, and there is no reason to believe that even if amphibian melanophores are directly innervated, nervous control is not significant to the normal rhythm of color change. Parker (1930), working on Hyla versicolor verified Hogben's findings. Redfield (1918) working on the horned toad, Phrynosoma cornutum, believed that contraction of the melanophores, in this form at least, is brought about by the cooperation of the nervous system and the secretion of the adrenal gland. Again, Hogben and Mirvish (1928) repeating experiments on the chameleon, concluded that the pigment cells are under direct control, since it was possible to evoke pallor by stimulation of the cord in isolated segments after the circulation had been cut off. According to these investigators, it is unlikely that adrenalin plays any significant part in the determination of excitement pallor as was suggested by Redfield's work on Phrynosoma. Although many investigators have shown experimentally that hormonal substances can cause melanophores of fishes to react, there is no reason to believe that such substances play the important part. It has been definitely shown by many investigators that in these forms the chromatophores are under direct control of the autonomic nerves, with the stimuli acting through the visual organ. Up to date only one case has been definitely shown to be an exception to this generalization. Lundstrom and Bard (1932), in a paper devoted to the action of the pituitary secretion on the