374 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



we are faced with an intrinsic change in the morphogenetic potential of the graft, in the 

 sense of an elevation or even of a qualitative change. The remarkable fact is that this 

 ability seems to persist beyond gastrulation. 



Various other experiments also performed on the neurula stage (Gallera, 1951, 

 1952; Okada and Hama, 1945a) have shown that the archenteric roof is an 

 inducing system w4iich gradually evolves and is plainly established when the 

 urodele neural plate is surrounded by a pigmented hem. At this stage, each region 







/ ,■/' 



^ 





Fig. 44. Comparison of the inductive capacity of prechordal endomesoblast and chordal 

 material taken from an early gastrula. (a) Limitation of the grafts, prechordal area stippled, 

 chordal area hatched, (b) An extensive induction caused by the prechordal graft, (c, d) 

 Anterior (c) and posterior (d) sections of this structure, which proves to be a cyclopic acromerit 

 continued by a deutomerit, with a fine otic vesicle, (e, f) Result of implanting chordal 

 territory, which has induced a whole head and even a part of the notomerit. (e) Shows a 

 paraphysis (dorsal to the brain) and two otic vesicles; in (f ) a small limb bud has grown to 

 the right of the rhombencephalon. An olfactory pit was also present. From Gallera, 1949. 



