EARLY ORGANOGENY 



129 



[TAIL BUD SOMITES 



IIND LIMB 



YOLK MASS 



Organ fields or anlagen of the closed neural tube stage. 



jaw. The oral suckers appear as V-shaped, pigmented, adhesive, mu- 

 cus-secreting glands at the ventral end of each sense plate. They 

 reach their maximum development at the 6 mm. stage and then begin 



Photograph of the neurenteric canal of the late neurula stage in the frog: 



sagittal section. 



