ykpl*\ 



blp 



H s Pf d l 



ect en d\ nch 



FIG. SS5. Development of the Frog. A F, segmentation; G, overgrowth of ectoderm; H, 1, 

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

 nervous system, notochord, and enteric canal ; L, newly -hatched tadpole, b/.cwl. blastoccele ; 

 U p. blp'. blastopore ; &/!. 6/-2. gills ; br. cl. depressions marking position of future gill-clefts ; 

 c.. eye; ect. ectoderm ; end. endoderm ; ent. enteron ; /. br. f ore -brain ; 1<. br. hind-brain; 

 ). br. mid-brain ; >,id..f. medullary fold ; riui. pr. medullary groove ; mcs. mesoderm ; my. mega- 

 meres ; iiii. micromei-es ; nch. notochord; n. e. c. neurenteric canal; pcdm. proctodseum ; 

 pin. pituitary iiivagination ; ret. commencement of rectum ; si: sucker ; .?/>. cd. spinal cord ; 

 sf^d.M. stomodseum ; t. tail ; yl: yolk cells ; irk. pi. yolk plug. (A D, F H, and J from 

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



