420 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



phenomenon to experimental analysis and found that he could control this kind 

 of neuralization by temporarily submitting the ectoblast to media of an increased 

 pH; the lowering of Ca^* concentration also acts in the same way. In addition, 

 these conditions if not duly controlled tend to dissolve the coat and the inter- 

 cellular cement and to cause cytolysis. The type of neuralization obtained in the 

 various types of experiments, some on whole embryos and others on explants, 

 showed a wide variation. In explants, however, the thickness of the neural 

 epithelium and its folding often resembled brain, and exceptionally, acrencephalic 

 strvictures were recognizable. Some of the illustrations show mesenchyme, and 

 the organization looks better in such cases. The author insisted on a close relation 

 between such abnormal conditions and the cytolytic effect exerted on cells. He 

 showed that mechanical lesions could sometimes exert a similar effect and that 

 abnormal behavior of ectoblast was more frequent in the presence of dead cells 

 and debris. He even went so far as to attribute the inducing effect of various 

 chemicals to their toxicity. The question is whether the autonomous neuralization 



O.p. ( 



« ye 



Fig. 8i. Results of the reaggregation of the anterior (mostly prechordal) part of the neural 

 plate of a newt neurula. (a, b) Cases with relatively simple pattern ; (c) case displaying a com- 

 plex pattern; o. p. - olfactive placodes; tel. - telencephalic parts. From Boterenbrood, 1958. 



