120 



H. H. NEWMAN. 



coelom; while the right anterior coelom has a posterior prolon- 

 gation extending as far as the posterior end of the stomach. The 

 preoral ciliated band is triangular and the posterior end of the 

 postoral band is turned well forward toward the mouth. 



At two weeks (Fig. 10) the anterior coeloms of the two sides 

 have fused above the pharynx to form a continuous vesicle. The 

 left anterior coelom is still separate from the posterior ccelom, 

 which is now quite large. The posterior prolongation of the 

 right anterior coelom has become relatively small in caliber, in 

 fact has begun the process of rudimentation. 



At twenty-four days (Fig. u) the left anterior ccelom has 



.pnl. 



m. a. c. 



oes 



-Ihyc. 



int.-, 



PC. 



f.h.p. 



rp.c. 



FIG. 12. Advanced Bipennaria larva seen from the ventral surface, showing 

 left hydrocoele well developed. 



FIG. 13. Young Brachiolaria larva, seen from the dorsal surface, with reversed 

 asymmetry. Primitive tentacles (p.t.) are shown arising from the hydrocoele of the 

 right side. Right hydropore (r.h.p.) and right posterior ccelom (r.p.c.) The 

 preoral lobe has become modified into the attachment organ of the simplified 

 Brachiolaria, with median sucker (ra.s.) and lateral suckers (/.s.). The remaining 

 lettered structures are explained in previous legend. 



