COLOUR CHANGES 527 



planted the more primitive method of hypophysial regulation. Loss of the 

 hypophysis is without effect on the colour response of Fundulus, which is 

 still able to change from pale to dark on a black background and to make 

 the reverse change on a white background, as well as a normal fish. The 

 times of these colour changes are very rapid, occurring in one or two 

 minutes, in contrast to the lengthy periods of several hours required for 

 colour changes in elasmobranchs, where the chromatophores are regulated 

 by pituitary secretions (70). 



The xanthophores and erythrophores of teleosts respond to background 

 changes independently of the melanophores. In Fundulus and in Holo- 

 centrus it has been found that colour bands involving lipophores can be 

 produced by incisions in the fins, and the presence of antagonistic nerve 

 fibres bringing about concentration or dispersion of lipophores has been 

 assumed on the basis of the same kind of evidence as that obtained in the 

 study of melanophore innervation. In the case of the erythrophores of 

 Holocentrus, electrical stimulation of the medulla causes contraction, and 

 section of peripheral nerves brings about expansion of the colour cells. 

 The last result appears to be due to cessation of tonic concentrating 

 impulses. Pituitary extracts made from Holocentrus are without effect on 

 the erythrophores. The xanthophores of Fundulus, however, are dispersed 

 by intermedine (28, 50, 74). 



Apart from background responses chromatophores are also involved in 

 the nuptial coloration of teleosts. These breeding liveries, in the male or 

 female, result from localized accumulations of melanophores or lipophores 

 in definite patterns, or from regulation of the degree of chromatophore 

 expansion. For example, in males of Fundulus a dark ocellus appearing on 

 the dorsal fin during the breeding period represents a massing of melano- 

 phores. In the Adriatic perch Serranus scriba, the nuptial dress can be 

 produced by pituitary extracts, which bring about peripheral expansion of 

 lipophores (54, 58). 



The Japanese labrid Halichoeres poecilopterus shows pronounced sexual 

 dimorphism, and the mature males acquire a permanent colour pattern 

 which is markedly dissimilar from that of the female (p. 494; Fig. 11.8). 

 These colour patterns are brought about by differences in the arrangement 

 and relative numbers of various chromatophores in the skin. In the normal 

 male, melanophores and guanophores are scattered over the whole 

 scale, and the former are greatly expanded. Together with the xantho- 

 phores they are responsible for the bottle-green colour of the body. The 

 tail is bluish in colour due to guanophores, and bears reddish spots result- 

 ing from concentrations of erythrophores. The appearance of sexual colora- 

 tion in the male parallels the hypertrophy of interstitial tissue in the testis, 

 and castration causes a reversion of coloration in the male to the immature 

 and female condition. In consequence the melanophores on the body con- 

 tract and degenerate along with guanophores. Xanthophores gradually 

 disappear over the body and are replaced by erythrophores, and a reverse 

 change takes place in the tail. As a result the fish becomes reddish in colour, 



