ANATOMY OF HOLOTHURIANS. 



211 



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 



Y\gA52.Pen(acta frondosa. t, tentacles; I, longitudinal muscles; r, retractor mus- 

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

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

 polian vesicles; am, ampullae: a, a', pseudo-haemal contractile vessels (from Cams); 

 0, ovary; ov, mduct. Drawn by J. S. Kiugsley from a dissection made by the author. 



and paler than the ovarian tubes. The water enters the 

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



