Stage Number 



Age -Hours AT I6°C 







UNFERTILIZED 



Staqe Number 



Age -Hours at I6X 



7.5 



32-CELL 



Stage Number 



Age- Hours AT l&'C 



13 



50 



NEURAL PLATE 



8 



14- 



62 



GRAY CRESCENT 



MID-CLEAVAGE 



NEURAL FOLDS 



3.5 



9 



15 



61 



TWO- CELL 



LATE CLEAVAGE 



ROTATION 



4.5 



10 



26 



FOUR- CELL 



DORSAL LIP 



16 



12 



5.1 



6.5 



II 



34 



NEURAL TUBE 



EIGHT- CELL 



MID-OASTRULA 



42 



SIXTEEN-CELL 



'1 



64 



UTE GASTRULA 



TAIL BUD 



(From "Stages in the Normal Development of Rana pipiens," by Waldo Shum- 

 way. Reprinted from Anat. Rec, 78, No. 2, October 1940.) 



27 



