bl.coel 



i/k.pl 



aft, 



DEVELOPMENT OF THE FROG. (From Parker and Haswell after Ziegler's models 



and Marshall.) 



A-F, segmentation. , overgrowth of ectoderm. //, 7, establishment of germinal layers, 

 y, /f, assumption of the tadpole-form and establishment of nervous system, notochord, and enteric 

 canal. Z,, newly-hatched tadpole. />/. cod., blastocoel. blp.. blp.^ blastopore. br .1 6r.. 2 gills. 

 br. cl.^ depressions marking future gill-clefts. <?, eye. ect.* ectoderm, end., endoderm. ent., 

 enteron. f. b*-.^ fore-brain h. br. hind-brain. /. br,, mid-brain, md. f., medullary fold?. 

 md. gr., medullary groove, mes.^ mesoderm. mg-* megameres. mi., micromeres. nch.^ no 

 tochord. n.e.c., neurenteric canal, pcdm.^ proctodaeum. pty.< pituitary invagination. rect., 

 commencement of rectum, sk.^ sucker, sp, cd., spinal cord. st. din.^ stomodaeum. /., tail 

 yk., yolk cells, yk. />/., yolk plug. 



