DEVELOPMENT OF CUCUMARIA ECHINATA. 



383 



Explanation of textfìgures. 



Diagrams showing the transformations of the internal cavities of 

 Cucumaria echinata. The cavities encircling the body-axis are shown 

 as flattened out in a plane and as seen from the exterior. The mid- 

 dorsal line is represented by a vertical line, hydroccele drawn with 

 heavy lines, enterocœle hatched, and gut (shown in figs. A and B) 

 stippled. Arrows indicate either separated parts or the ends just united. 



Fig. A. — The coiled archenteron not yet divided. Fig. B. — Gut 

 separated from the hydro-enterocœle, the latter is constricted into two 

 parts. Fig. C. — Hydroccele separated from enterocœle, the latter again 

 constricted into two parts. Fig. D. — Hydroccele giving out several 

 lobes, and dorsal pore formed ; right and left enterocœle divided. Fig. 

 E. — Four of the primary tentacles and rudiment of midventral radial 

 canal formed, the two enterocceles united on the right side. Fig. F. — 

 All the five tentacles and radial canals and Polian vesicle can be seen ; 

 posterior end of midventral radial canal dilated, madreporic vesicle 

 formed in the course of primary stone-canal. Fig. G. — Hydroccele-ring 

 closed at the left dorsal interradius, enterocœle much extended, leaving 

 an S-shaped partition which gives rise to the mesentery. 



dp — dorsal pore, en' — enterocœle before separation from hydrocœle, 

 g — gut, g'— do. before separation from hydro-enterocœle, /// — hydro- 

 coele, hy — do. before separation from enterocoele, Idr — left dorsal radial 

 canal, len — left enterocœle, Ieri —do. before separation from the right 

 one, Ivr — left ventral radial canal, mes - -rudimentary mesentery, mp — 

 madreporic vesicle, tnvr — midventral radial canal, pc — pore-canal, 

 pd — pedicel canal, pv -Polian vesicle, rdr — right dorsal radial canal, 

 ren — right enterocœle, ren' — do. before separation from the left one, 

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

 canal, /,_ 5 — primary tentacles situated on middorsal, right dorsal, right 

 ventral, left ventai and left dorsal interradius respectively. 



