212 SALT-WATER FISHES 



from the action of sunlight. As a consequence, or, at any 

 rate, as an accompanying condition, this left side is henceforth 

 colourless. The left eye also works over to the right side, 

 eventually taking up a position in line with the right. These 

 remarkable metamorphoses are accompanied by a varying 

 degree of malformation in the head of the fish, the extremes 

 of which are perhaps marked by the plaice and halibut, the 

 former wearing a curiously wry expression on its face, the 

 latter, which is also the largest of the family, being, in facial 

 appearance, little different from a round fish. 



This final position of the eyes, both on the same side, 

 clearly separates the flat-fish from all flattened round fish, such 

 as the dory. Abnormal examples, having an eye on either 

 side, are not very rare, and these usually have both sides 

 similarly coloured, thus further conforming to the condition 

 of round fishes. Mr. Holt* has, however, described an adult 

 female sole, measuring 15 in., which had one eye on either 

 side, but, the colouring normal — -that is to say, confined 

 to the upper side. Though the abnormal eye was somewhat 

 impeded in its action by an overgrowth of skin and by sensory 

 filaments, there was no reason for supposing that the fish could 

 not see with it, or that, in fact, the uncoloured side was per- 

 manently out ot the sphere of influence of direct light. 



Another particular in which these flat-fishes, even in a 

 single species, show marked difference is the roughness or 

 smoothess of the skin. Thus, the flounder has rough scales, 

 and the turbot has no scales, but rough tubercles in their 

 place. But there is a wide range in either species. Flounders 

 from the Mediterranean are found to be quite smooth, while 

 those taken from the Baltic Sea are even rougher than those 

 on our coasts. Turbot, again, from the Norwegian fjords are 

 far more profusely studded with tubercles than those caught in 

 the English Channel, and often have tubercles on the lower 

 surface as well as on the upper. The plaice is yet more 

 * Sec /our/1. Mar. Biolog. Assoc, October, 1894, p. 188. 



