EXPERIMENTAL MODIFICATIONS 



75 





^•ts?:,'^' 



:^. 



#■ 





if 



v^-/>c 



'^^ 



^ib 



^ ; 



■P' '-^^ 



Fig. 29. Formation of atypical ectoderm in an amphibian egg treated with 

 ribonuclease at the morula stage (Brachet and Ledoux, 1955). 



•->-V,; 





» * 





»^. •■-<•■■■ 





■^-:^aii^ 







i§i^ 



Fig. 30. Formation of a nervous system in an amphibian egg treated with a 

 mixture of RNA and ribonuclease at the morula stage (Brachet and Ledoux, 



1955). 



