Fig 169 Presumptive organ-forming areas in the amphibian late blastula and be- 

 ginning gastrula. (A, B) General epiblast and hypoblast areas of the early and late 

 blastular conditions, respectively. The hypoblast is composed mainly of entodermal or 

 gut-lining structures, whereas the epiblast is a composite of ectodermal (i e epiderma 

 and neural), mesodermal, and notochordal presumptive areas. Observe that the epiblast 

 gradually grows downward over the hypoblast as the late blastula is formed. (C) Be- 

 ginning gastrula of the urodele, Triton. (Presumptive areas shown according to Vogt 

 '29 ) (D) Same as above, from vegetative pole. (Slightly modified from Vogt, 29 J 

 (E) Lateral view of beginning gastrula of anuran amphibia. (F) Dorsal view of the 

 same (E F derived from description by Vogt. '29, relative to Rana jiisca and Bom- 

 binator: also Pasteels: J. Exper. Zool., 89, relative to Discoglossus.) Observe that an 

 antero-posterior progression of somites is indicated in C and D. 



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