Fig. 64. — Development of the frog. 



A — F, se.smentation ; 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. c<eI. segmentation cavity ; blp^ blp' . blastopore ; (5;-l, />;■-, gills ; /'/-. cl. branchial 

 arches ; *:. eye ; ect. ectoderm ; end. endoderm ; cnt. enteron ; f. hr. fore-brain ; 

 h.br. hind-brain; 7u.b . mid-brain; ;;;(/. _/I medullary fold; ;;/(/. ^r, medullary 

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

 nch. notochord ; n. c. c. neurenteric canal ; Pcdi7i. proctodaeum ; pty. invagina- 

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

 rectum; sk. sucker; sp. cd. spinal cord; stdin. stomodEcum;' t. tail; yk. 

 yolk-cells; yk.pl. yolk-plug which fills the blastopore. (A— D, F — H, and J 

 rom Ziegler's models; E, I, K, and L after Marshall.) 



