180 



ZOOLOGY. 



a nervous cord to the eye at the end of the ray. It may be 

 discovered by pressing apart the ambulacral feet along the 

 median line of each arm. Fine nerves are sent off to each 

 sucker, passing through the opening between the calcareous 

 plates and extending to eacli ampulla, thus controlling the 

 movements of the ambulacral feet. 



am, ampullae, the ambulacral feet projecting below; b, coeca or liver. Drawn by 

 A. F. Gray, under author's direction. 



The mouth (Fig. 125, m) is capacious, opening by a short 

 oesophagus into a capacious stomach (Fig. 125, .<?) with thin 

 distensible walls, and sending a long lobe or sac (Fig. 125, /) 

 into the base of each arm; each sac is bound down by two 

 retractor muscles attached to the median ridge lying be- 

 tween the two rows of water-sacs (ampullae, see also Fig. 126). 



a C~^ 



Fig. 126. Diagram of the water-system of a star-fish, a. madreporic body: 6, 

 stone-canal; c. circumoral water-tube; d. water-tubes to the arms; e, ampullae; 

 /, feet or suckers. After Brooks. 



The stomach ends in an intestine. The intestine suddenly 

 contracts and ends in a minute rectum situated in an angle 

 between two of five fleshy ridges radiating from the centre 



