Normal Plates of the Development of Lepidosiren paradoxa and Protopterus annectens. 



13 



jKiratloxa. 



Metotic 

 mesoderm segments 



Nervous System 



Eye 



Otocyst 



Visceral 

 clefts 



Urogenital 

 System 



Stage 



Mesoderm not yet 

 segmented. 



Mesoderm segments 



(about 7) faintly dis- 



cernible with central 



coelomic cavity be- 



ginning to appear. 



About 12? 



Myocoeles present 



widely open. 



Deep layer of ectoderm of 



medullary plate decidedly 



thickened and beginning to be 



more than one cell thick. 



(Very slight longitudinal de- 

 pression along centre of me- 

 dullary plate. The latter has 

 grown down into a distinct 

 keel by multiplication of its 

 deep layer cells in the region 

 of the mesial plane.) 



Medullary folds distinct. Me- 

 dullary keel well developed. 



Medullary folds have met along 

 middle of trunk region. 



Neural rudiment still solid. 



Solid optic 

 rudiment. 



Begins as down- 



growth of deep 



layer of ectoderm, 



13 



14 



16 



18 



(3 solid rudi- 

 ments [Agar].) 



Pronephric 



swelling oppo- 



site anterior 



segments. 



20 



