XVI 



ECHINODEEMATA 



493 



to extend over the dorsal surface of the stomodaeum, and its posterior 

 end sweeps round to the right, across the ventral surface of the 



oesophagus. In this way it is gradually transformed into a cn-cle, 

 the two ends of which meet on the right side of the mouth, which 

 thus becomes completely surrounded. The lobes project into the 

 stomodaeum as tentacles covered by stomodaeal ectoderm. This 



