222 



THE HOLOTHURIOIDEA 



Opening into the anterior and dorsal region of the cloaca by a 

 common duct are the respiratory trees, two large tubes which give 



FIG. II. 



1. Transverse section of one of the Holotlmrinae. (Modified from Ludwig and Lang.) 



2. Transverse section of the body-wall of HoMhuria impaticns, Forskal. 



3. (A) "table " and (B) " biscuit " ( spicule of the same. 



4. Transverse section of the radius of an Actinopod Holothurian. (After Lang.) 



5. Left side view of the* anterior region of Holothvria tubnlosa, Gmel., from which the 

 left side of the body-wall has been removed. 



6. (A) perforated disc, and (B) branching tod spicule of HolothitriaforslMli. 



a, ampulla ; a.v, anti-mesenterial blood-vessel ; 6, " biseult " spicule ; b.i; blood-vessel ; ZMC, 

 body-wall ; c, coelom ; car, calcareous ring ; c.c, circular canal ; c.ep, coelomic epithelium ; c.m, 

 circular muscles ; c.p, podial canal ; ct, cutis ; (Line*, dorsal mesentery ; d.n, deep nerve ; ep, 

 epidermis ; ep.c, epineural canal ; g, goiiad ; g.d, genital duct ; g.p, genital pore ; ', intestine ; 

 l.d.r, left dorsal radius ; l.m, longitudinal muscles ; Lines, left mesenterial ; l.r.t, left respira- 

 tory tree ; l.v.r, left ventral radius ; md, madreporite ; m.r, median ventral radius ; m. v, mesen- 

 terial blood-vessel ; p, podium ; p.c, pseudhaemal canal ; p.n, podial nerve ; pr, peripharyngeal 

 coelom ; p.v, polian vesicle ; r.c, radial canal ; r.d.r, right dorsal radius ; r.ines, right mesenterral 

 fold ; r.r.t, right respiratory tree ; r.v.r, right ventral radius ; s.n, superficial nerve; t, tentacle ; 

 t.a, tentacle ampulla; ta, "table" spicule in 2. 



off numerous side - branches ending blindly in tufts of slender 

 twigs (Fig. I. 1, l.r.t and r.r.t). Coming off from the base of the 



