UI.1 



THE NOTOCHOED. 

 Fig. 20. 



61 



Transverse Section through the Embryonic Region of the 

 Blastoderm of a Chick at the time of the formation 

 of the Notochord, but before the appearance of 

 THE Medullary Groove. 



ep. epiblast ; hy. hypoblast ; ch. notochord ; me. mesoblast ; 

 ylc. yolk of germinal wall. 



Fig. 21. 



Transverse Section of a Blastoderm incubated for 

 18 hours. 



The section passes through the medullary groove mc, at some 

 distance behind its front end. 



A. Epiblast. B. Mesoblast. C. Hypoblast. 



m.c. medullary groove ; m.f. medullary fold ; ch. notochord. 



