l- h , 885 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 o^ 

 nervous system, notochord, and enteric canal ; L, newly-hatched tadpole, bt.coel. blastoccele ; 

 /,//> />/' Uaatopore ; M. 7-2. gills ; />;. cl. depressions marking position of future gill-clefts ; 

 ,- eve eel. ectoderm ; end. endoderm ; ent. enteron ; /. &} fore-brain ; h. br. hind-brain ; 

 >. /,",-. mid-brain ; >,/. f. medullary fold ; md. gr. medullary groove ; met. mesodemi ; mg mega- 

 meres ml. micromeres; nch. notochord; n. e. c. neurenteric canal; pcdm. proctodamm ; 

 jy. r.ituitary invagination ; vet. commencement of rectum ;-*k. sucker; up. c<i. spinal cord; 

 *t;>t,,i. stomodajum ; f. tail ; ? /i-. yolk cells ; yk. pi. yolk plug. (A D, F H, and J from 

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



