248 



GASTRULA-ARRESTED EMBRYOS 



Evidence relevant to this last point is meager, indeed; but there 

 is at least some. 



Utilization of Endogenous Carbohydrate 



In 1948, Gregg made a comparative study of carbohydrate uti- 

 lization by developing hybrid and R. pipiens embryos. Normal 



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I I I I I I I I I II I I I 



I 7 e 10 12 14 17 18 19 



DEVELOPMENTAL STAGE 



20 



21 



Fig. 10. Endogenous carbohydrate of developing Rana pipiens em- 

 bryos. Upper curve, total carbohydrate; middle curve, glycogen; lower 

 curve, free carbohydrate. (From Gregg, 1948.) 



embryos (Fig. 10) are characterized by the fact that they begin 

 to oxidize their carbohydrate store not later than the onset of 

 gastrulation and continue thereafter to do so to such an extent 

 that, by the time they are hatched larvae, they have little more 



