Forebrain 



Midbrain 



Spinal 



Enteron 

 Endoderm 

 Notochord 

 Ectoderm 



Animal pole 



2-cell stage 



Yolk 

 Mesoderm 



Older embryo in section 



Gill arches 



"Anal" pit 



Older embryo with neural groove closed 



I ^f^^iT'^^C^''^?:: Neural fold 



-Neural groove 



Primitive streak 



Ectoderm 

 - .. Endoderm 



■ ■ :^. Blastocoe 

 — ' ' - Gastrocoel y^ 



Vegetal pole 



4-cell stage 



8-cell stage 



Gastrula 

 in section 



Blastopore 



Early gastrula 

 Figure 237. Early development of the frog. (After Huettner.) 



Early gastrula 

 in section 



357 



