100 



ANIMAL LIFE 



around the forehead, its socket moving with it, until both 

 eyes and sockets are transferred by twisting of the skull to 



PIG. 51. The wide-eyed flounder (Platophrys lunatus). Adult, showing both eyes on 

 upper side of head. 



the upper side. In some related forms or soles the small 

 eye passes through the head and not around it, appearing 

 finally in the same socket with the other eye. 



Thus in almost all the great groups of animals we find 

 certain kinds which show metamorphosis in their post- 

 embryonic development. But metamorphosis is simply 

 development; its striking and extraordinary features are 

 usually due to the fact that the orderly, gradual course of 

 the development is revealed to us only occasionally, with 

 the result of giving the impression that the development is 

 proceeding by leaps and bounds from one strange stage to 



FIG. 52. Development of a flounder (after EMERY). The eyes in the young flounder 

 are arranged normally, one on each side of head. 



another. If metamorphosis is carefully studied it loses its 

 aspect of marvel, although never its great interest. 



