PROTECTIVE COLOEATION. 141 



our shores, but one of these is as yet only known from a single 

 specimen. So far as is known, all these species show a change 

 of colour in response to changes in the environment ; it is only 

 in Solea vulgaris that they have been carefully studied by 

 Mr. Cunningham. 



A series of beautiful plates illustrate the changes of colour. 

 The colour of the living fish is yellowish-grey with large, 

 irregular, dark blotches and small white spots ; this colour is 

 confined to one side of the body ; the opposite side, which rests 

 upon the ground, is, as in other flat fishes, white. 



When the fish was lying upon a " coarse,, bright, clean 

 gravel," consisting of yellow and orange-coloured pebbles 

 mixed with others bla.ck and white, its colours were very 

 conspicuous, though nothing approaching an exact similarity 

 to the ground could be seen ; on the whole it is inconspicuous,, 

 though the white streak along the edge of the fins was very 

 evident. 



When a sole was placed in a white porcelain dish and ex- 

 posed to strong daylight, the colours became much paler ; the 

 blotches, instead of being brown or black, were pale orange; 

 but, curiously enough, the white marks, which might have been 

 expected to increase in size, or at least to persist, disappeared. 



A sole j)laced in a tub containing some washed coal and 

 removed from the light became very dark in colour ; but the 

 result of this was to render the white band along the fins, 

 extremely conspicuous. The changes of colour depend not on 

 the nature of the ground, but on the amount of light ; for the 

 blackest ground did not produce the darkest coloration in the- 

 fish until the amount of light was diminished. The sole does 

 not become uniformly coloured on a uniformly coloured ground.. 

 The fact that it does become, on the whole, lighter on light- 

 coloured ground and darker on dark-coloured ground, is to be: 



