FATE OF BLASTOPORE, ETC., IN CHELOXIA. jo 



iiia}^ 1)0, i^^athererl from the uccoinpanying- diagrains. Woodcut X, A 



Woodcut X. 



A 

 X 





Diagrams showing three successive 

 stages in the development of the 

 posterior part of the embryo. 



Yt. Plug. 



gives the .surface (liugnuu and the h'ne of origin of the gastral and 

 peristomal me.-ohla.st. Tlie traiisveivse .section througli the line A B in 

 that diagram is given in Series I,/, and diagrammatically in Woodcut 

 XI, D. The groove hetween the yolk-plug and the outer lip of the 

 blastopore should ideally go into the midst of the mesoblast, dividing 

 it into the parietal and visceral layers, and in some sections it does 

 actually go much further into the înesoblast than in Series I, f. The 



