Fio. 43. — Three transverse sections across the caudal 



END OF the medullary GROOVE OF a CHICK EMBRYO WITH SEVEN 



SEGMENTS. (After Minot ) 



A, section through one of the secfnients. B, section posterior to the segments. 

 C, section just in front of the primitive streak. Afc^. gr, medullary groove; nck^ 

 notochord; Ec^ ectoderm; 7nesy mesoderm; En^ entoderm ; Seg, mesoblastic 

 somite. 



128 



