114 



H. H. NEWMAN. 



The completed gastrula is somewhat elongated (Fig. 6) and the 

 anterior end of the archenteron reaches about half way to the 

 apical end. This stage is attained at about thirty hours after 

 fertilization. 



,c.p. 



..c.p 



FIGS. 1-6. Early stages, blastulas and gastrulae, of Patiria. c.p., the thinned- 

 out anterior portion of the archenteron in process of forming the coelomic pouches. 



Post-gastrula Stages. The changes leading up to the typical 

 Bipennaria condition involve several distinct types of differenti- 

 ation: (a) the development of well-defined dorsal and ventral 

 surfaces, together with a relative shortening of the ventral 

 surface, which thus becomes concave, and a relative lengthening 

 of the dorsal surface, which becomes convex; (b) the differenti- 

 ation of the external ciliated bands; and (c) the development of 

 the cceloms. 



The larva at about fifty hours (Fig. 8) shows the blastopore 

 moving slightly toward the ventral surface, the somewhat convex 

 contour of the latter, the slight thickening and bulging of the 

 region destined to form the preoral ciliated band, and the enlarge- 

 ment and thinning out of the anterior end of the archenteron to 

 form the pharynx and the anterior cceloms. The changes in 

 larval form and the development of the ciliated bands are so 

 nearly identical with those described for other asteroids that they 



