STRUCTURE OF SEA-CUCUMBER 



307 



canals. Sense organs are represented by the tentacles, 

 which sometimes have " ear-sacs " at their bases, and by 



Fig. 166. — A small sea-cucumber. — From a specimen. 



T., One of the ten branched tentacles, homologous with 

 tube-feet ; i?., a radial line, corresponding to an 

 internal radial water-vessel, which gives off ampullae 

 internally and tube-feet [T.F.) externally. 



tactile processes on the dorsal surface of some of the 

 creeping forms. 



From the terminal or ventral mouth, surrounded by five. 



