534 



INVEKTEBKATA 



CHAP. 



Ophiuroidea, and Echinoidea respectively ; the radial canals of the 

 Holothuroidea, the rudiments of which are represented by the 

 secondary lobes of the hydrocoele, would therefore, on this hypothesis, 

 not be homologous with those of other Echinoderms. 



Fig. 397. — Three views of young Auricularia larvae of Synapta digitata viewed from the 

 dorsal surface, showing the division of the coelom. (After Metschnikoff.) 



A, the coelom still undivided, but extending far backwards. B, the coelom divided into anterior 

 and posterior portions. C, the posterior portion of the coelom divided into right and left halves, a.c, 

 anterior division of the coelom ; calc, calcareous body ; j).coe, posterior division of the coelom ; cil.long, 

 longitudinal ciliated band ; coe, undivided coelomic sac ; lp,G, left posterior coelom ; mp, madeporic 

 pore ; oes, oesophagus ; r.^^-e, right posterior coelom ; st, stomach ; .ttom, stomodaeum. 



But the whole of this theory is shattered by our knowledge of the 

 development of Cucumaria planci, first described by Selenka but 

 worked out with care by Ludwig (1891). 



