THE ORGANIZER 



211 



PRESUMPTIVE MEDULLARY PLATE 



DORSAL LIP 

 BLASTOPORE 



ANURA STAGE I I 

 SHOWING REGIONS TO BE EXCISED OR TRANSPLANTED 



ORGANIZING IMPLANT 



HOLTFRETERS SOLUTION 

 BLASTOCOELE 



VENTRAL LIP 



GASTRULAR SLIT 



DORSAL LIP 



STAGE 10 



ORGANIZING IMPLANT 

 VENTRAL LIP 



HOLTFRETERS' SOLUTION 

 BLASTOCOELE 



DORSAL UP 



NOTOCHORD 



MEDULLARY PLATE 

 STAGE 12 



