DEVELOPMENT OF COELOM 



609 



quickly assunies a crescentic form, and gives off five blunt out- 

 growtlis, which ai'c the rudiments of the radial canals, and the 

 terminal tentacles. It remains in connexion with the anterior 

 coelom by a narrow neck, wliicli later becomes the stone-canal. 

 That on the viglit .side se])arates completely from the right 

 anterior coelom ; it remains small, and forms tlie madreporic 

 vesicle (Fig. 287, A'^ rJnj) of the adult. In the Ophiopluteus 



Asteroid Ophiuroid 



ECHINOIO HOUDTHUROID CRINOIO 



Fia. 287. — Diagrams of the mode of formation and division of the coelom in Ecliino- 

 dermata. «.c, Anterior coelom ; coe, primitive coeloniic rudiment ; int, intestine ; 

 l.a.c, left anterior coelom ; l.hji, left liydrocoel ; l.j).c, left posterior coelom ; ocs, 

 oesophagus ; ^).c, posterior coelom ; r.a.c, riglit anterior coelom ; r./i)/, right hydro- 

 coel ; r.jj.c, right posterior coelom ; st, stomach ; sfom, stomodaeum. 



and in the larva of Asterina gihJtosa (v. iufnt) it occasionally 

 takes on a form similar to that of the liydrocoel ; from whicli 

 circumstance, as well as from tlie similarity in its mode of 

 origin, it is here regarded as a right liydrocoel, i.e. a rudi- 

 mentary fellow of tlie organ wliich develops into tlie water- 

 vascular system. 



In Auricularia (Fig. 287, D) the coelomic vesicle, after the 

 pore-canal is formed, divides into an anterior and a posterior 

 half. The posterior ])art then divides into riglit and left halves, 



VOL. I 2 1; 



