166 



TEXT-BOOK OF EMBRYOLOGY. 



Ectoderm 

 I 



Neural 



tube 



i 



Primitive 

 segment 



Ectoderm 



i 

 Notochord 



Visceral 

 Mesoderm 



I 

 Coelom 



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 aortae. 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. 



