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 
Fig. 152.—Pentacta frondosa. t, tentacles; J, longitudinal muscles; #, retractor mus- 
cles of the tentacular system; i, intestine; ¢, cloaca; b, respiratory tree; vr, water- 
vascular ring or ring-canal, v, radial water-vascular canal; m. madreporic body; pp, 
polian vesicles; am, ampulle; a, a’, Ls pep rn contractile vessels (from Carus) , 
0, ovary; Ov, oviduct.—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 (2), oozes out of 
