370 



GERMINAL ORGANIZATION INDUCTION PHENOMENA 



Fig. 41. Grafts of prechordal neuroepithelium, not including prechordal plate, on the 

 abdomen of a tail-bud stage. Left row (a, d, g), the young neurulae used as donors. Middle 

 row, the hosts with their grafts ; right row the donor in the process of healing. From Gallera, 



1947- 



chordal material. This observation had already been made in several earlier 

 investigations, and was utilized by Pasteels and inyself to coin the theory of 

 morphogenetic potentials (p. 343). The dorso-lateral decrement of such properties 

 can be recognized when working on the corresponding presumptive areas of the 

 gastrula and even of the blastula, and also when depressing the scales of potentials 

 by toxic substances (p. 350, 422). It will not be necessary in this review to give 

 more argviments in support of this well-established notion. 



In 1947, when I still thought it likely that the obtaining of an acrencephalon 

 was due more to the intensity and precocity of the induction than to some specific 

 cause, Gallera and Damas simultaneously studied in my laboratory the conse- 

 quences of depriving small neurectoblast pieces of the inducing action exerted 

 on them by the archenteric roof (Fig. 41). The pieces were carefully detached 



