Star-fish 59 



action. 1 The under surface of a star-fish's 

 body has an opening or mouth leading to 

 the gullet and digestive organs, from 

 which there is an outlet on the upper part 

 of the body. The under surface of each 

 arm is grooved, and has rows of contractile 

 tubular organs each terminating in a sucker, 

 known as the " tube feet." These structures 

 are worked by the contraction and relaxation 

 of the muscular fibres which surround the tube, 

 and are thus under the control of the animal's 

 nervous system. 



The nervous system of a star-fish is derived 

 from and is in close connection with the proto- 

 plasmic elements of the ectoderm. The central 

 part of this system is composed mainly of two 

 rings of nerve cells and fibres which surround 

 the animal's gullet. From these circum-oral 

 rings radial nerves extend throughout the 

 length of each of the animal's arms; they supply 

 branches to its entire muscular system, and 

 also to the sensory organs. In addition to the 

 radial system of nerves, although doubtless 



1 Jelly-fish, Star-fish, and Sea-urchins, by G. J. Romanes, 

 P- 255. 



