110 



CHAPTER in. 



COLOUE. 



The colour and markings of the upper side of the common sole, so far as they are 

 permanent and characteristic of the species, have already been described. But, as was 

 mentioned in connection with that description, the skin of the fish is capable during life of 

 exhibiting considerable changes in the intensity and to some extent in the quality of its 

 colours. It is exceedingly difficult to study these changes of colour in a living fish if the 

 material on which it is placed consists of fine particles, like sand or mud. For the fish 

 will persist in burying itself, and it is impossible to keep the skin free from particles of 

 ihe material, so that an accurate estimation of the colour under particular conditions 

 can scarcely be made. It is not difficult to keep a sole alive and in a healthy condition 

 for several days or even weeks in a shallow vessel supplied with a current of sea water. 

 In order to study the colour-changes carefully I kept specimens in this way, allowing 

 them to rest either on a solid surface or on a material of coarse texture without fine 

 particles, namely, coarse gravel or broken coal thoroughly washed in running water. 



It is generally believed that the colour and marking of the sole's skin assimilates 

 itself to the colour and texture of the ground on which it rests. The following 

 observations were made in order to obtain definite results as to the extent and 

 character of this assimilation : I found that the contrast between the markings and 

 the ground-colour of the skin was most conspicuous when the fish was lying on a coarse 

 bright clean gravel. The gravel which I used had a general orange tint, but it 

 contained, besides yellow and orange coloured pebbles, a considerable number of black 

 and white. The appearance of the fish when resting on this gravel is shown in Plate I. 

 The ground colour is a greenish grey, and on this ground all the spots and markings 

 ever present in a sole are well marked. The principal dark blotches are very 

 conspicuous and well defined ; the irregular lighter bands which connect them ramify 

 in the spaces between them. The blotches are in places quite black, the black being 

 always confined to the outer part of the scales, the anterior part of these being always 

 somewhat lighter. The small white spots alternating with the blotches are also fully 

 expressed. The dark spot at the outer end of the pectoral is pronounced. It is 

 evident from the drawing that there is no exact similarity between the colour and 

 markings of the fish and the appearance of the surrounding gravel ; but it is also 



