166 



TEXT-BOOK OF EMBRYOLOGY. 





Ectoderm 



Notochord 



Visceral 

 Mesoderm 



Ccelo 



Fig. 139. — Transverse section of chick embryo (2 days' incubation). Photograph. 

 The parietal mesoderm (lying above the ccelom) is not labeled. The two large vessels under 

 the primitive segments are the primitive aortas. Spaces separating germ layers are due to 

 shrinkage. 



Mesoderm 

 (mesenchyme) 



Neural tube 







Ectoderm 



Pharynx 



Entoderm 



Fig. 140. — Transverse section through head region of chick embryo of 42 hours' 

 incubation. Photograph. 



