REGENERATION IN EGG AND EMBRYO 



235 



Similar phenomena have been made out by Driesch in the devel- 

 opment of the archenteron of the same forms. At the end of the nor- 



FlG. 65. A. Blastula of sea-urchin beginning to gastrulaie. Cut in half as indicated by line. 

 Two rows of figures to right show development of upper and lower halves. B. Later gastrula 

 cut in half. Two rows of figures to right show later development. C. End of gastrulation 

 process. Embryo cut in half. Two rows of figures to right show later stages of each half. 

 D. Formation of endodermal pouches from inner end of archenteron. Embryo cut in two. 

 Two rows of figures to right show later stages. 



mal gastrula period of the starfish embryo, there is produced from the 

 inner part of the archenteron two outgrowths, or pouches, that later 

 constrict off to give rise to the coelom sac and water-vascular system. 



