VII 1 ECHINODERMA TA— ONTOGENY 5 1 7 



The water pore lying on the right side of the mesentery (now formed) disappears 



Fig. 415.— Longitudinal section of a larva of Cucumaria doliolum (after Selenka). 1, Frontal 

 prominence with enclosed jelly-like siibstunee ; ■_', tentacle vessels; 3, (5, 15, 14, 13, radial 

 vessels ; 5, stone canal ; S, madreporite ; 4, Polian vesiide cut oft' ; 7 and 12, coeloni, enterocal 

 vesicle ; 9, anus ; 10 and 11, the first two tube-feet ; IG, circular canal of the water vascular 

 system ; 17, oesophagus ; 18, mouth ; 10, mesenchyme cells ; II, III, IV, V, ciliated rings. 



later, and still later the madreporitic vesicle opens into the body cavity, and thus 

 becomes the secondary inner madreporite. 



