82 STAGING OF AMPHIBIAN EMBRYOS 



1+1. Medullary plate forming even with an extruding yolk plug, 



1+2. Normal yolk plug but gaetrular surface rough, Indicating early disin- 

 tegration. 



hj). - k6. Neunilae vrith extruding yolk plugs. If these develop the embryos 

 have severe caudal abnormalities. 



h^ . - 55' Heml-embryoa, due to incomplete invagination. 



5'+. - 55 • Rudimentary abnormal embryos due to failure to incorporate yolk. 



56. Hemi-embryo in which there is slight development of the head region. 



57- - 59- Anterior end fairly normal in heml-embryos, Internal structures 

 very abnormal. 



