172 FISHES CHAP. 



stream near Ivy Bridge have become much lighter since the pollu- 

 tion of the water by white china clay. 1 As an illustration of the 

 necessity of vision to such colour-changes, it may be mentioned 

 that blind Fishes cannot vary their tint in this protective fashion. 

 A blind Turbot living upon a light sandy bottom differed from 

 its fellows in being much darker and more conspicuous. Dark 

 Trout have been observed among their light-coloured brethren in 

 a chalk stream in Hampshire, but the former were invariably 

 blind, probably, as their larger size indicated, through age. 2 



Of other forms of protective resemblance, reference may be 

 made to the bottom-feeding Fiat-Fishes (Pleuronectidae), many of 

 which have the upper surface of the body coloured with various 

 shades of brown, speckled with black or light specks or blotches, 

 in harmony with the prevailing tints of the sandy banks which 

 usually form their feeding-ground. When disturbed these Fishes 

 court concealment, and render themselves still less conspicuous by 

 partially burying themselves in the sand. Many of the Skates 

 and Eays, which have a white ventral surface, have the back 

 mottled and coloured in accordance with the colour of the sea- 

 bottom, but in this case it is possible that the advantage lies 

 in enabling the Fish to secure passing prey by concealing its own 

 whereabouts. 



Striking examples of protective coloration occur among the 

 Pipe-Fishes and Sea-Horses (Syngnathidae),which usually frequent 

 groves of Zostera, Fucoids, and other sea-weeds. A British 

 species of Pipe-Fish (Siphonostoma typhle), 3 which lives among the 

 blades of the sea-grass, Zostera, is olive-green in colour, and is a 

 typical example of protective resemblance both in colour and in 

 the slender elongated shape of the body. Similar protective re- 

 semblances are noticeable among the Sea-Horses, the coloration 

 varying with the general hue of their environment of sea- weed ; but 

 the climax is certainly reached by the singular Australian species, 

 Phyllopteryx eques (Fig. 388). 4 In this Fish the skin is produced 

 into numerous long, flattened, branched filaments, which are pro- 

 longed from the extremities of spine-like outgrowths of the dermal 

 skeleton, and marked by alternate bands of brown and orange, 5 



1 Poulton, op. cit. p. 82. 2 Ibid. p. 86. 



3 Cunningham and MacMunn, op. cit. p. 773. 



4 C. Stewart, quoted by Poulton, op. cit. p. 67. 



5 Saville Kent, op. cit. p. 186, describes the colours of the living Fish as " various 

 shades of light crimson and lilac." 



