166 



TEXT-BOOK OF EMBRYOLOGY. 



Ectoderm 



Neural 

 tube 



Ectoderm 



Coelom 



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

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

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

 shrinkage. 



Mesoderm Neural tube 



(mesenchyme) 



Ectoderm 



Pharynx 



Entoderm 



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

 incubation. Photograph. 



