202 



THE MOSAIC STAGE OF DIFFERENTIATION 



40' 



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Fig. 97 



Mosaic development and self-differentiation of isolated regions of the neurula 

 (Urodele) explanted in inorganic culture medium. A, Epidermal vesicle, g days 

 after explantation. B, Section through A; note ridges and folds (cf. fig. 13). 

 C, Notochords, 11 days after explantation. D, Endodermal vesicle, representing 

 an everted gut with the endothelial cells directed outwards. E, Section through 

 D showing the endodermal cells secreting outwards into the medium, 13 days 

 after explantation. (From Holtfreter, Arch. Entwmech. cxxiv, 193 1.) 



