Fig. 64. — Dcvclutjnicni. of tlit frog. 



A — F, segmentation ; G, overgrowth of ectoderm ; H, I, establishment of germinal 

 layers ; J, K, assumption of tadpole-form and establishment of nervous system, 

 notochord, and enteric canal ; L, newly-hatched tadpole. 



bl. cxl. segmentation cavity ; blpy blp' . blastopore ; bi^^ br-. gills ; bj-. cl. brancliial 

 arches ; c. eye ; cct. ectoderm ; end. endoderm ; cnt. enteron ; f. br. fore-brain ; 

 h. br. hind-brain; in.b . mid-brain; vid.f. medullary fold; md.gr. medullary 

 groove ; incs. mesoderm ; ing. large lower cells ; mi. small upper cells ; 

 nch. notochord ; n. c. c. neurenteric canal ; pcdin. proctodasum ; pty. invagina- 

 tion of ectoderm which will form the pituitary body ; ret. commencement of 

 rectum ; sk. sucker ; sp. cd. spinal cord ; stdin. stomodEeum ; /. tail ; yk. 

 yolk-cclls ; jj'/u-.//. yolk-plug which tills the blastopore. (A— D, F— H, and J 

 rom Zicgler's models; E, I, K, and T. after IMarshall.) 



