Fig. 156, A-H. — Amphibian gastrulation and neural plate formation; diagrammatic; 

 chorda-mesoderm indicated by deeper, ectoderm by lighter line-shading, entoderm by cell 

 boundaries. A~E, median sections; F, same stage as E in transverse section; G, H, neurula in 

 dorsal view and in transverse section (from Spemann, 1936, Experimentelle Beitrdge zu eitur 

 Theorie der Entwicklung. Springer, after chart by V. Hamburger and B. Meyer; also Spemann, 

 1938)- 



