E 



H 



I 



FIG. ]6 

 Continuation of Fig. 15. Later stages of the sea-uicliiii Faraccntrotas (from 

 BoN-ERi) showing fate of the three original zones. E, 16cell stage; F, blastiila ; 

 G, inwandering of mesenehyme-cell fioni tlie lower clear zone; H, beginning of 

 gastrulation ; I, J, invagination of pigmentoil zone to form tlie arclienforon. 



