124 



STRUCTURE OF RADIATA. 



mals ; and it is onjy in a few that even these imperfect eyes 

 can be discovered. In the inferior Eadiata, not the slightest 



Fig. 65. SHELL OF STAR FISH. 



traces of a nervous system have yet been discovered; and 

 it is very doubtful whether any such structure exists in 

 them. It is only among the higher 

 Radiata that any locomotive power 

 exists ; and this is usually so feeble 

 that the animals remain in the same 

 locality during the greater portion 

 of their lives. Generally speaking, 

 there is a period in the history of 

 each species, in which there is a 

 more active movement, that serves 

 to prevent the accumulation of indi- 

 viduals in one spot ; but this move- 

 ment is of a purely automatic 

 character, rather resembling that of the " zoospores " of plants, 

 than the intentional change of place of the higher animals. 



Fig. 66. NERVOUS SYSTEM 

 OF STAR FISH. 



