Cleavage, Blastulation and Gastrulation 



227 



ure is considerably greater than that calcu- 

 lated by Waddington ('39) for the force of 

 invagination in the Triton embryo (i.e., 

 0.34 mg. per square millimeter). Until more 

 forms are studied, the significance of svich 

 calculations cannot be judged. It appears 

 inconceivable, in view of the general knowl- 

 edge relating to osmotic pressure in cells, 

 that half the cell (the part bordering the 

 blastocoele) could swell while the half 

 toward the future archenteric cavity shrinks. 

 The changes in cell shape that accompany 

 gastrulation can scarcely be osmotic in 

 origin. 



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