410 



EMBRYOLOGY 



itself frorn the rest, and unites with the dorsal wall of the 

 larva. As its further development shows, this abstricted 

 portion of the archenteron corresponds to the vaso-peritoneal 

 vesicle of the other Echinodermata (Fig. 179). It communi- 

 cates directly with the outside world by means of the dorsal 

 pore, just as in certain Asteroidea. It is not until this stage 

 that a constriction makes its appearance in the posterior 



Fig. 194. 

 Fig. 194. — Optical longi- 

 tudinal section of an Auricu- 

 laria larva of Holothuria tuhti- 

 losa (after Selenka). A, 

 auus; D, intestine; JB, entero- 

 coele ; H, hydrocoele ; M, 

 mouth ; P, dorsal pore ; W, 

 ciliated band. 



^m. -]./■ 



Fig. 195.— Longitudinal section of a larva 

 of Cucumaria doliolum, somewhat diagram- 

 matic (after Selenka). A, anus; Am, ambu- 

 lacral (radial) vessels ; D, intestine ; E, entero- 

 coeles; F, feet; M, mouth ; P, dorsal pore, 

 leading through the stone canal to the water- 

 vascular ring, Wr ; T, tentacular vesicles ; 

 Wr, water- vascular ring. 



third of the vaso-peritoneal vesicle (in Holothuria tubulosa), 

 which divides the vesicle into the hydrocoele, connected with 

 the dorsal pore, and the less extensive enterocoele (Fig. 194 



