FIG. 119. Development of the Frog. A-F, cleavage; G, overgrowth of 

 ectoderm; H, I, establishment of germ-layers; J, K, assumption of tadpole-form 

 and establishment of nervous system, notochord and enteric canal (archenteron) ; 

 L, newly-hatched tadpole, bl. coel, blastoccole; blp. blp', blastopore; br r . br", 

 cutaneous gills; br. cl, branchial arches; e, eye; ect, ectoderm; end, endoderm; 

 erit, enteron;/. br, fore-brain; h. br, hind-brain; w. br, mid-brain; md.f, medullary 

 fold; md. gr, medullary groove; mes, mesoderm; mg, megameres; mi, micromeres; 

 nch, notochord; n. e. c, neurenteric canal; pcdm, proctoda3um; pty, pituitary in- 

 vagination; ret, commencement of rectum; sk, sucker; sp. cd, spinal cord; stdm, 

 stomodaeum; t, tail; yk, yolk cells; yk. pi, yolk plug. (From Parker and Haswell, 

 after Ziegler and Marshall.) 



206 



