378 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



As the authors express it (their p. 512); "with regard to inductive capacity, the median 

 dorsal Hp, though similar in general to the other parts, possesses in a latent condition an 

 additional characteristic, which is lacking elsewhere and which cannot be other than the 

 quality that later causes this section to be imbued with the head-organizing effect" (ex- 

 pression apparently used with the acrencephalon in inind). Finally, this fundamental paper 

 mentions that in frog gastrulae, uninvaginated material of the early blastoporal lip is al- 

 ready capable of inducing the forebrain when inserted in the wall of newt gastrulae. In 

 Anurans, this property appears earlier than in Urodeles. To be complete, let us mention 

 that in a further investigation Okada and Takaya (1942) examined whether the combina- 

 tion of the two inductors could produce a normal embryonic axis. Such was the result in 

 several cases, but in others, the notomeritic inductor had a debasing effect on the acrome- 

 ritic one. It is also useful to record that the potencies of the uninvaginated part of the young 



Fig. 47. Modification of the inductive capacity of a given presumptive area, considered 

 either before or after its invagination, a-a' to c-c^ concern newt embryos, (a) Induction of a head 

 by the invaginated material at stage (a) of Fig. 45, i.e., the inner part of the quite young 

 blastoporal lip. (a') Induction of trunk and tail by the uninvaginated material of the same 

 stage; (b-b') same difference relative to invaginated and unvaginated material of stage (b), 

 Fig. 45; (c-c') induction caused respectively by the anterior and posterior part of the ar- 

 chenteric roof as shown in fig. 45 (c) ; (d-d>) induction by invaginated and uninvaginated 

 material ofafrog gastrula; here, a head is obtained in both cases. From Okada and Takaya, 



1942. 



