FLAT-FISHES. 223 



The well-known " flat-fishes," such as the sole, dab, 

 flounder, plaice, brill, turbot, &c., are in strong force in 

 all our large marine aquaria, where they attract much 

 attention on account of their unexpected graceful 

 movements in the water. It is only there that we 

 can thoroughly understand the marvellous changes 

 which have been effected in the life-history of these 

 fishes, by means of which both their structure and 

 habits have been slowly adapted to their present 

 condition. Their popular name of " flat-fishes " is apt 

 to lead one astray in his conclusion as to the cause 

 of this flatness. It is not due to the fishes lying 

 with the belly or ventral side downwards ; but to 

 their habitually lying on one side. They are com- 

 pressed, not depressed, as in the skates. Then only 

 one side is coloured, that next the ground being very 

 light. But the coloured part is usually called the 

 "back," whereas we now see it is only a special 

 adaptation to the really wonderful modifications these 

 animals have experienced. Moreover, the observer 

 may notice how soles and other flat-fishes having 

 a uniform dull neutral tint usually settle down on 

 the sandy part of the bottom of the tank, and add 

 still further to their concealment by dusting them- 

 selves over with the fine sand, which rises and partly 

 settles down over them, so as to form an admirable 

 screen. Such flat-fishes as the plaice, on the other 

 hand, will be often seen to select that part of the 

 bottom where gravel is abundant ; and then we may 



