FIG. 64. Development of 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, (x 10.) 



bl. cccl. segmentation cavity ; blp, blp', blastopore ; bri, br^, gills ; br. a. branchial 

 arches ; e, eye ; eel. ectoderm ; end. endoderm ; ent. enteron /. br. fore- 

 brain ; h. br. hind-brain ; m. br. mid-brain ; md. f. medullary fold ; md. gr. 

 medullary groove ; mcs. mesoderm : mg. large lower cells ; mi. small upper cells ; 

 nch. notochord ; n. e. c. neurentenc canal ; pcdm. proctodaeum ; pty. invagina- 

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

 sk. sucker ; sp. cd. spinal cord ; stdm. stomodasum ; t. tail ; yk. yolk-cells ; 

 yk. pi. yolk-plug which fills the blastopore. (From Parker and HaswelTs 

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

 after Marshall.) 



199 



