THE STUDY OF CHICK EMBRYOS 



I Primitive 

 *C streak 



Blood island 



FIG. 30. Dorsal surface view of a twenty-hour chick embryo, showing primitive streak, 

 head process and extent of mesoderm (after Duval). X 17. The lines A, B, and C indicate 

 the levels of the corresponding sections shown in Fig. 31. 



Ectoderm 



Neural plate 





Mesoderm 



Ectoderm 



Notochordal plate 

 Primitive knot 



Mesoderm Entoderm 



FIG. 31. Transverse sections through the embryonic area of a twenty-hour chick. 

 X 165. A, through the head process; B, through the primitive knot; C, through the 

 primitive streak. 



