

-rT---::^'^' 





'■•« 



.,^. - 





^r^x^ 



^.^■^•- 



^y 



M . 





Figure 15. Flat medullary plate obtained by treating advanced gastrulae 

 with mercaptoethanol (M/300) for two 'to three days. Chorda and somites 

 are normal (Brachet and Delange-Cornil, 1959) . 







i^Kt-"^ 



i 



if ♦. 





^ '-■ J' 



■<^''A 



'*'*«*' 



Figure 16. Thickened nervous system in a frog embryo treated with dithio- 

 diglycol (Brachet and Delange-Cornil, 1959) . 



