Class 4i. Holothuroidea. 141 



otter viscera is forced out througli the anus. The lost organs are replaced by- 

 regeneration. Other forms (Synapia) when in-itated, constrict transversely 

 and break into several pieces. 



The following may be cited as examples : Cucumaria, tube-feet in five double 

 rows from the mouth to the anus, arborescent tentacles : Holothuria, with 

 scattered tube-feet, conical on the dorsal surface, cylindrical on the ventral,, 

 tentacles peltate : Psolus, with the tube-feet confined to the flattened ventral 

 sui-faoe, calcareous scales dorsally : Synapta, without tube-feet, vermiform, with 

 small tentacles, and microscopic calcareous anchors in the transparent skin. The 

 genera mentioned are all found in European seas. Recently a number of peculiar 

 abysmal forms, with flattened ventral sm-face, and long processes of the body, 

 have been discovered {Elpidia and others). 



