PLATE 1 



EXPLANATION OF FIGURES 



67 Normal embryonic stages 1 to 13. 



1 One-celled ovum. 



2 Two -celled ovum. 



3 Three-celled ovum. 



4 Early 4-celled ovum with large blastomeres. 

 4' Late 4-celled ovum with small blastomeres. 



5 Six-celled ovum. 



6 Eight-celled ovum. 



7 Twelve-celled ovum. 



8 Sixteen-celled ovum. 



9 Thirty-two-celled unilaminar blastocyst. 



10 First endodermal mother-cells. 



11 Earliest medullary plate and considerable yolk in gastrocoele. 



12 Expanded and attenuated vesicle with endodermal cells still almost en- 

 tirely under medullary plate. 



13 Ellipsoid blastocyst eccentric in albumen and with endodermal cells 

 spreading toward equator. 



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