XIII 



PfTYLUM CHOKDATA 



281 



B 



bl.corj 





FIG. 950. Development of the Frog. A F. segmentation ; G, overgrowth of ectoderm ; //, /, 

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

 nervous system, notochord, and enteric canal ; L, newly-hatched tadpole, bl. cael. bla-tn- 

 ctt-le ; blp. blp'. blastopore ; br.l. br.->. gills ; br. d. branchial arches ; c. eye ; ect. ectoderm : end. 

 endoderm ; ent. enteron ; /. br. tore-brain ; //. br. liind-hrain ; m. br. mid-brain ; mil. f. 

 medullary fold; md. gr. medullary groove; nn'x. inr^nderm; ma. megameres ; mi. niirro- 

 meres ; nch. notochord; n. c. c. neurenteric canal; pcdm. proctod;eum ; pty. pituitaiy 

 invagination ; ret. commencement of rectum ; sk. sucker ; sp. cd. spinal curd ; st.dm sd.niii- 

 dseum ; t. tail; yk. yolk-cells; yk. pi. yolk lug. (A D, FH, and J from Ziegler's 

 models ; E, 1, K, and L after Marshall.) 



