80 STAGING OF AMPHIBIAN EMBRYOS 



21. Exo-gastrula in which 2/5 of yolk is unincorporated. 



22. Gastrulation achieved although dorsal lip has been damaged. 

 25. Exo-gastrula in which 2/5 of yolk is unincorporated. 



2U. Heml-gastrula. 



25. - 26. Embryonic areas attempting to develop without incorporated yolk. 



27. - 59- Various degrees of exo-gastrulatlon. 



1+0. Fairly normal yolk plug but irregular dorsal lip which will condition 

 abnormalities in the embryo. 



