EMBRYOLOGY 

 68 



Several questions now arise. How can the roof of the archenteron by 

 mere contact with the ectoderm influence it to become a nervous system? 

 Will any ectoderm form a nervous system if stimulated by the roof of the 

 archenteron? Is the ectoderm completely incapable of forming anything by 

 itself ? These questions will be considered in the chapter that follows. 



