Explanation of Plate V. 



(All the figures are semi-diagramma ic representations of reconstructions 

 from sections, magnified about 120). 



Fig. I. — Old gastrula with coiled archenteron. Ectoderm shown in 

 section, archenteron in external view with its lumen indicated by a 

 broken line ; mesenchymatous cells in blastoeœle not represented. 

 Viewed from right. 



Fig. 2. — Do., ventral view. 



Fig. 3. — 'Early doliolaria of the same stage as that shown in Text- 

 fig. E. Viewed from left side. 



Fig. 4. — Completed doliolaria of the same stage as that shown in 

 Textfig. F. Viewed from left side. 



Fig. 5. — Early doliolaria, same as fig. 3. Only the hydrocœle is 

 shown. Posterior view. 



Fig. 6. — Completed doliolaria, same as fig. 4. Only the hydrocœle 

 is shown. Posterior view. 



blc — blastoeœle, bip — blastopore, cb^ — ciliary bands, dp — dorsal 

 pore, en' , g' , hy f — enterocœle, gut and hydrocœle not yet separated from 

 each other, Idr — left dorsal radial canal, len — left enterocœle, len' — do. 

 before separation from the right one, Ip — left primary pedicel, Ipc — left 

 pedicel canal, Ivr— left ventral radial canal, mes — rudimentary mesen- 

 tery, mp — madrcporic vesicle, mvr — midventral radial canal, pr — pore- 

 canal, prl — preoral lobe, pv — Polian vesicle, re — open ring-canal, rdr — 

 right dorsal radial canal, ren — right enterocœle, ren' — do. before 

 separation from the left one, rp — right primary pedicel, rpc — -right 

 pedicel canal, rvr— right ventral radial canal, stc — stone-canal, stc'— 

 primary stone-canal, stm — stomodœum, stm' — ectodermal thickening for 

 the stomoda^um, t x _ h — primary tentacles situated in middorsal, right 

 dorsal, right ventral, left ventral and left dorsal interradius respectively. 



