AMPHIBIA. 



223 



Fig. 65. CLEAVAGE OF OOSPERM OF FROG (from Haddon, after Ecker). 

 The numbers indicate the number of segments. Dotted lines show 

 position of succeeding planes of segmentation. 



Fig. 66. BLASTULA AND GASTRULA OF FROG (after Gotte). All are 

 sections. A, Partly segmented oosperm. B, Completely segmented 

 oosperm. C, D, E, Stages in formation of gastrula ; al, archenteron 

 (mesenteron) ; bl, segmentation cavity ; blp, blastopore ; ep and ep', 

 nervous and superficial layers of ectoderm ; hy t endoderm ; m and m', 

 mesoderm ; y.%, lower layer cells. 



