372 



AQUATIC VERTEBRATES 



This condition has probably been developed through the principle of 

 natural selection, discussed more fully in Chapter 34, and the floun- 

 der or sole shows that this is not just accidental. This fish spends 

 much of its time lying on its side against the ocean floor and when it is 

 swimming it even swims on its side. The side which is usually under- 

 neath, left side, has become light colored, whereas the side which is 



Photos by Winchester 



Fig. 25.5. Varieties of fish. From left to right and top to bottom these are : Spotted 

 jewfish, Promicrops itaiara; Toadfish, Opsanus tan; Long Nosed Gar, Lcpisostcus 

 osscus; Singapore Carp, Cyprinus carpio; Pike, Esox lucius; and Red Tailed Catfish, 



Phractoccphalus hemilopterus. 



usually exposed to light is darker. Curiously enough, the left eye, 

 which was formerly on the left side in a normal position, migrates 

 through the skull during embryonic development and comes out on the 

 right side along with the right eye. An eye pressed into the dirt on the 

 ocean floor would be of no value, but in this unusual position it can 

 function. 



Some fish can even change the color and pattern of their bodies to 

 blend with their surroundings. The flounder is another good example of 



