[IL] 



THE NOTOCHORD. 



61 



Fig. 20. 





Pransverse Section through the Embryonic Region of the 

 Blastoderm of a Chick at the time op the formation 



OF THE XoTOCHORD, BUT BEFORE THE APPEARANCE OF 



THE Medullary Groove. 



p. epiblast ; Ay. hypoblast ; ch. notochord ; me. mesoblast ; 

 yL yolk of germinal wall. 



Fig. 21. 



Transverse Section op a Blastoderm incubated for 



18 HOURS. 



The section passes through the medullary groove mc, at some 

 listance behind its front end. 



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



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



