DEVELOPMENT OF CUCUMARIA ECHINATA 939 
and third ciliary bands. The left pedicel is a little earlier in 
appearing than the right, while neither of the two can be said 
definitely to be anterior to the other in position. 
13. The original position of the primary tentacles is decidedly 
interradial, but their bases gradually shift towards the respective 
radial canal according to a definite asymmetrical feature. The 
one in the left dorsal interradius appears last. 
14. The Polian vesicle appears at the free end of the ventral 
limb of the hydrocoele ring, while about the same ‘ime the 
axial sinus is formed as a secondary dilatation of the middle part 
of the pore-canal. The dorsal pore has now opened between 
the second and third ciliary bands. 
15. The hydrocoele rmg closes in the left dorsal imterradius. 
This is clearly shown by the position of the rudiments of the 
dorsal and ventral radial canals of the left side, appearing usually 
before the closure of the rmg. Of the four paired radial canals 
the right dorsal appears first, while the left ventral is the last to 
appear. 
16. Fusion of the right and left enterocoeles occurs on the right 
side, while on the other side the two vesicles lie close but 
separated. This intervening portion gives rise to the mesentery, 
which at last bends im an S-shape in agreement with the coil of 
the gut in the future. The gut is almost solid, leaving but very 
narrow lumen. Blastocoele jelly is most massive in the doliolaria 
stage, and mesenchymé cells thickly cover all the internal 
vesicles, without, however, forming any definite cell-layer. 
17. The latter half of the doliolaria stage may be distinguished 
by calling it metadoliolaria. Here degeneration of the pre-oral 
hood and ciliary bands sets in, while muscles and nerves are 
differentiated, besides the further completion of hydrocoele and 
enterocoele. Calcareous deposits, too, make their first appear- 
ance in this stage. They appear in three places: the wall of the 
axial smus, the bases of the tentacles, and the integument of 
the posterior part of the body. 
18. In the course of a week or more the larva changes into 
a creeping stage, pentactula. The five tentacles have now 
a few branches and the third pedicel appears at last. The gut 
