AN-ATOMT OF HOLOTHURIANS. 129 



on one side arises the " respiratory tree," which has but one 

 main stem, and is only occasionally held in place by mus- 

 cular threads. The branches are numerous, and are smaller 



Fig. S^.—Pentacta frondosa. t, tentacles; I, longitudinal muBcles; >■, retractor mus- 

 cles of the tentacular system; z, intestine; c, cloaca; 6, respiratory tree; vr, water- 

 vascular ring or nng-canal, v, radial water-vascular canal; m, madreporic body; pp, 

 polian vesicles; am, ampullae ; a, «', pseudo-hsemal coutractile vessels (from Carus); 

 0, ovary; ow, o\aduct. — Drawn by J. S. Kingsley from a dissection made by the author. 



and paler than the ovarian tubes. The water enters the 

 cloaca (c), passes into the respiratory tree (5), oozes out of 



