CHAPTER 12 

 COLOUR CHANGES 



I took several specimens of an octopus which possessed a most mar- 

 vellous power of changing its colours, equalling any chameleon, and 

 evidently accommodating the changes to the colour of the background 

 which it passed over. Yellowish green, dark brown, and red, were the 

 prevailing colours. . . . 



Charles Darwin, 1832 



Certain animals have acquired the power of altering their shade or colour 

 in relation to the character of the background and incident illumination. 

 These animals have special pigment cells or chromatophores in their skin, 

 and it is by means of concentration or dispersion of pigments in the chro- 

 matophores that the colour changes are brought about. Chromatophores 

 are found in five different phyla of marine animals — echinoderms, annelids, 

 molluscs, Crustacea and vertebrates — and they probably have evolved 

 independently on several different occasions. They reach their highest 

 development in cephalopods, malacostraca and vertebrates, but they are 

 also present in some echinoids, polychaetes, leeches and pteropods. The 

 subject of colour responses has been extensively reviewed, among others 

 by Abramowitz (3) and Parker (48, 53, 54). 



CHROMATOPHORES 



Chromatophores are classified according to the kind of pigment or reflect- 

 ing material which they contain. Melanophores are dark chromatophores 

 containing brown or black melanin pigments. Lipophores are cells bearing 

 red or yellow carotenoid pigments, and are termed erythrophores or 

 xanthophores according to their colour. Allophores is a term sometimes 

 used for red chromatophores bearing reddish non-carotenoid pigments. 

 Guanophores, also called leucophores and iridophores, contain particles 

 of guanine in the form of small granules or plate-like crystals. By move- 

 ments of these several kinds of pigments in various ways or combinations, 

 the animal is able to bring about changes in its colour pattern, and the 

 alterations in coloration may reach a high degree of complexity in those 

 animals with well-differentiated chromatophoral systems (14, 54). 



Chromatophore Movements 



There are two different ways in which chromatophoral movements are 

 effected, exemplified in cephalopods, Crustacea and fishes. In cephalopods 

 the colour cell itself is controlled by attached muscle fibres, which are 

 capable of dilating it (Fig. 12.1). In Crustacea and fishes, on the other hand, 



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