210 COLOUR IN NATURE chap. 



in some fishes and many birds ; or in increased 

 growth and development of the cuticular structures 

 in the male, associated usually with a great develop- 

 ment of optical colours and of pigment ; or as in 

 many mammals there may be simply a special 

 development of the exoskeleton, not associated with 

 a great increase of pigment, or any special brilliancy 

 of tint. Beauty in mammals is, however, usually due 

 rather to form than to bright colour. 



The Colours of Fishes 



I. Tropical Fishes. — Among the colours of fishes, 

 those of the forms inhabiting the neighbourhood 

 of the coral reefs of warm seas must be especially 

 mentioned. We have already seen how brilliant are 

 the tints of the coral polypes themselves, and the 

 same brilliancy seems to occur almost universally 

 among the inhabitants of the waters round the reef 

 In fishes, however, the brilliant colours are probably 

 produced not by pigments but by structure. The 

 colours fade with extraordinary rapidity after death 

 or removal from the water, and according to those 

 who have seen the fish in their natural condition, 

 the coloration is at best quaint and striking rather 

 than beautiful. Generally speaking, the tints seem 

 to be very vivid and hard, with a lack of light and 

 shade ; the occurrence of sharply contrasted bands 

 or spots on a bright ground is exceedingly common. 

 Bright green, blue, red, and yellow seem to be among 

 the commonest colours, and there are some striking 

 instances of sexual dimorphism. Thus in Ostracion 

 ornata the male has a ground colour of grass-green, 



