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THE BIOLOGY OF THE FROG 



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FlG. 16. — Segmentation of egg. (After Schultze.) A, two-cell stage, 

 with the beginning of the second furrow ; B, eight-cell stage, showing 

 the cross furrow at the animal pole; E, eight-cell stage; C, D, F, G, 

 sixteen-cell stages, showing variations in the plan of cleavage ; //, thirty- 

 two-cell stage. (From Morgan's "Development of the Frog's Egg.") 



