294 



THE STARFISH. PHYLUM E CH I NOD E RM AT A 



through a pecuhar metamorphosis, in which its left and right 

 sides become the oral and aboral surfaces. 



BEHAVIOUR 



Like most animals the starfish moves towards the side from 

 which certain stimuli come. In crawling one (or sometimes two) 



sev 



Fig. 219. — Part of a view from above of the oral half of a starfish [Asterias 

 Yubens), after removal of the alimentary canal. 



amb.r. Ambulacral ridge ; amp., ampullae of tube-feet ; ax.s., axial sinus, with stone canal and axial organ ; 

 gon., generative organ ; perist., peristome ; ret.m., retractor muscle of the stomach ; sep., septum ; 

 T.b., Tiedemann's body. 



of the arms is directed forwards. On this leading arm each tube- 

 foot — not moving in step with any other — is extended in the 

 direction of the arm, makes contact with the ground, and then 

 swings back, so that it moves the body forwards like the legs of 

 other animals. On a vertical surface, or when a starfish meets a 

 resistance, the foot acts as a sucker, and the animal is pulled 

 forwards. On the other arms the tube-feet behave in the same 

 manner but swing to and fro in the direction in which the animal 



