ANATOMY OF HOLOTHURIAN8. 



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. 89. Pentacta frondosa. t, tentacles; /, longitudinal muscles; r, retractor mus- 

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

 vascular ring or nng-canal, t>, radial water-vascular canal; m. rnadreporic body; pp, 

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

 o, ovary; ov, oviduct. 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 (#), oozes out of 



