94 



THE SEAS 



curious twisting takes place in their head region and the eye 

 from one side travels round so that eventually both eyes 

 come to lie on the same side of the head. The fish then 

 turns over and settles on the bottom on its eyeless side. 

 In some species it is the left eye which changes its position 

 and in others the right eye, and it is rather unusual to find 

 a fish with both its eyes on the opposite side to that typical 

 for the species. 



Other fishes, however, are flattened quite normally. 

 The skates for instance are flat from above downwards and 

 the eyes keep their same relative position throughout life. 



Fig. 15. — Gurnard, showing the separated fin-rays of the pectoral fin, 



The gurnards are literally able to walk over the bottom. 

 Just in front of the big fan-shaped pectoral fin on each side 

 are three curved rigid spines, and if the fish be watched in an 

 aquarium it will be seen that when moving over the bottom 

 it is actually walking on the spines. The spines really 

 belong to the fin ; they are fin-rays which in the course of 

 time have broken away from the actual fin itself and 

 evolved into these curious legs, which probably have a 

 tactile purpose. (Fig. 15). 



Another way in which fins have been modified, is to form 



