534 



INVEETEBEATA 



CHAP. 



Ophiuroidea, and Echiuoidea respectively ; tlie radial canals ut' 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. 



B 



coe 



ci 



il.long 



mp 



*S\ cillong 



a.c 



calc 



cillong 



ac 



oes 



r.pc 



FIG. 397. Three views of young Anricularia larvae of Xi/intjitit diijitdia viewed from tin' 

 dorsal surface, showing the division of the coeloni. (After Metsclmikoff. ) 



A, the coeloni 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. .e, 

 anterior division of the coedoni ; <'</<, calcareous body ; p. coe, posterior division of the coeloni ; cil.ltniii, 

 longitudinal ciliated band ; me, undivided coelomic sac ; /./>.<, left posterior coeloni ; i/<, ni.-idrporic 

 port- ; ui'.x-, oesophagus; c.j'.r, right posterior coeloni ; .-/, stomach; xtnm, stoiiioilai-iiin. 



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

 development of Cucumaria planci, first described by Seleuka but 

 worked out with care by Ludwig (1891). 



