FIG. 64. Developmentrof the 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. 



l>l. ccel. segmentation cavity ; blp> blp' . blastopore ; br^, br*. gills ; br. cl. branchial 

 arches ; - e. eye ; ect. ectoderm ; end. endoderm ; ent. archenteron ; f. br. fore 

 brain ; h. br. hind-brain ; in. br. mid-brain ; md.f. medullary fold ; rnd.gr. medul 

 lary groove ; nies. mesoderm ; nig. large lower cells ; mi. small upper cells 

 nek. notochord ; n. e. c. neurenteric canal ; pcdm. proctodaeum ; pty. invagina 

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

 rectum ; sk. sucker ; sp. cd. spinal cord ; stdin. stomodaeum ; t. tail ; yk. 

 yolk-cells;^.//, yolk-plug which fills the blastopore. (From Parker and 

 Haswell's Zoology , A D, F H, and J from Ziegler's models ; E, I, K, and 

 L after Marshall.) 



