NEURULATION 



123 



material in a more or less "arbitrary" way, varying from case 

 to case. 



This power of regulation was also encountered in experiments 

 in which material of the organisation centre was explanted, 

 and cultured in a salt solution. In this case, it produced not 





\M.y 



Fig. 44. Above: Closing neurula of Triton taeniatus, seen from 

 dorsal, from ventral, and from the right side. Below: embryo de- 

 veloping from the dorsal half (after frontal transection of an early 

 gastrula) at the same stage of development. The latter embryo is 

 quite harmoniously built, as may be seen on comparison with the 

 normal embryo. After Ruud and Spemann. 



only notochord and muscular tissue, but, if sufficient material 

 was present (e.g. because several blastopore lips were cultured 

 together), ectoderm would be formed as well (Lopashov, 1935). 

 This ectoderm surrounded the other tissues, and here, too, in 

 part of it the formation of nervous tissue was induced. In this 

 way organ complexes were formed that had some faint re- 

 semblance to embryos. 



The organisation-field can also extend over indifferent 



