ADJUSTMENT OF FLATFISHES 447 



during the course of the present experiments. The fishes commonly 

 assumed a very different appearance when disturbed or when swim- 

 ming ' voluntarily' in the aquarium from that displayed when at 

 rest.^^ Such changes generally followed certain laws, though 

 there were abundant exceptions to these. 



1. A fish of pale or medium shade generally became darker^^ 

 when disturbed, and at such times dark spots or blotches commonly 

 came into view.^'^ In a few specimens highly colored red specks 

 appeared at such times. The resting condition was resumed in a few 

 minutes or seconds after the fish settled upon the bottom. These 

 phenomena were manifested even by those blinded specimens 

 which had secondarily become pale. 



2. In certain cases very dark fishes, which had recently been 

 considerably paler, assumed a lighter hue when caused to swim 

 around. These changes were so inconspicuous that I was no" at 

 first certain of their reality, but their ocurrence was confirmed by 

 observations upon at least three fishes, after transfer to the magne- 

 tite sand. 



3. When the fish was in the highly contrasted condition, with 

 conspicuous white and black areas, this appearance commonly 

 diminished, or even wholly disappeared, when the animal was dis- 

 turbed. Its skin then assumed a medium shade, and the markings 

 became inconspicuous. The same monotone was commonly 

 assumed when these fishes swam about without known external 

 stimulus. Indeed, in the case of certain specimens, I found it a 

 very easy matter to discern the fish's intention' to begin swim- 

 ming by the disappearance of the spots and the assumption of this 

 monotone. Thus fig. Ag was taken upon such an occasion. Upon 

 settling down upon the bottom, the skin pattern gradually came 

 into view, and generally attained its maximum distinctness within 

 comparatively few seconds. The effect of these latter changes 



^5 Pouchet, Van Rynberk, Townsend (op. cit.), and others, have called attention 

 to pronouced color differences, in some species, between the resting condition and 

 conditions of activity or excitement. 



^^ This darkening, under the influence of disturbance, is the only change of this 

 sort recorded by Van Rynberk, who believes it to be of constant occurrence. 



^^ Pouchet (op. cit., p. 76) records the appearance of such spots in the turbot. 



