Fia. 256. Dissection of Holothuj^a tubulosa. x h. 1. Feelers ; 2, feeler-ampullae ; S, 



"ring-canal ; 4, Polian vesicle ; 5, stone-canals ; 6, radial canal ; 7. one of a pair of 



longitudinal muscles ; 8, genital tubes ; 9, intestine ; 10, radiating muscles of 



cloaca; 11, base of respiratory tree ; 12, ventral blood-vessel ; 13. plexus of dorsal 



blood-vessel. (After Ludwig.) 



