Note on the Development of Cribrella oculata. 311 



2. Gastrulation appears in some cases to be effected 

 normally, though it has been as yet impossible to connect 

 the gastrulae with either the morula on the one hand, or 

 with the later larva on the other hand. 



In other cases the hypoblast appears to be formed either 

 by multipolar gastrulation, or by multipolar ingression of 

 single cells. 



3. The uniformly ciliated slightly oval larva, when hatched, 

 shows an epiblast with a pit at the posterior end, which is 

 either the ontogenetic or phyletic vestige of the blastopore, 

 containing a mass of nuclei and cytoplasmic strands in which 

 lies a hollow sphere of hypoblast, which is usually in contact 

 with the blastoporic pit, and filled with the same material 

 as surrounds it. 



4. The mesoblast is formed from two rudiments. The 

 first, or anterior, is constricted off from the front end of the 

 hypoblast, and the second, posterior, is later constricted off 

 from the hind end. The anterior divides almost entirely 

 into left and right hydrocoele and preoral coelom, and the 

 posterior divides into left and right enterocoele. 



Of these the preoral coelom survives mainly as the axial 

 sinus (as in Asterina and Bipinnaria), and the right hydro- 

 coele disappears by differential growth. It is never com- 

 pletely separated from the anterior coelom, and it is merely 

 merged into the latter. 



The left enterocoele gives rise mainly to the hypogastric 

 coelom (Goto), and the right enterocoele to the epigastric 

 coelom (Goto). 



5. At the dorsal posterior border of the anterior coelom, 

 immediately above the archenteron, is constricted off a small 

 vesicle, which soon becomes thin - walled, and closely re- 

 sembles the preoral sac of Balanoglossus. Before separation 

 from the preoral coelom, it is carried over to the right, as in 

 Fig. 4. It persists in the adult as a closed vesicle near the 

 madreporite, and apparently has been described in Asterina 

 by Macbride as a right hydrocoele. Bury describes thie same 

 organ in Bipinnaria and others (c/ Field) as a schizocoelic 

 contractile vesicle. 



6. The anterior end of the larva has three arras by which 

 VOL. XIV. X 



