388 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 

 A 



impi 



ent 



Fig. 55. Realization of a dorsal ectoblast fold, according to Nieuwkoop. A. A rectangular 

 piece of ectoblast is isolated from the animal pole region of a young gastrula. B. Folding 

 and pressing of this piece between two blocks of agar, fixed with needles to wax-bottom of 

 operation dish C. Similar folding and pressing between two layers of agar weighted by a 

 small glass bridge. D. Implantation of fold into an early gastrula in the dorsal midline, 

 near the border line between the prospective marginal zone and the neural area. 



A. animal pole; bl. -blastopore; ect. -ectoblast; m.-somitic area; n.-notochordal area; 

 nr.-neural area; V. vegetative pole. From Nieuwkoop et al., 1952. 



Fig. 56. Diagram giving the displacement of border lines between prospective marginal 

 zone, neural area and anterior ectoblast. This displacement is an effect of the implanted 

 fold on the kinematics. The areas over which displacement has taken place are roughly 

 hatched. Same abbreviations as in Fig. 55, plus: ent.-endoblast; impl. -implant. From 



Nieuwkoop et al., 1952. 



