EXTRA-EMBRYONIC MEMBRANES 



position occupied by the allantois, close beneath the porous 

 shell (Fig. 30). In addition to its primary respiratory function 

 the allantois serves as a reservoir for the secretions coming from 



neural tube 



notochord 



aorta 



mesenchyme 



mid-gut 

 entoderm 



amniotic cavity 



neural tube 

 notochord 



aorta 



mesenchyme 



mid-gut 



entoderm 



splanchnic 



mesoderm 



amniotic cavity 

 cloaca 



cloaca 1 



membrane 



yolk 



FIG. 33. Schematic longitudinal-section diagrams of the caudal half of the 



embryo to show the formation of the allantois. 



A, chick of about three days incubation; B, chick of about four lays in- 

 cubation. 



the developing excretory organs and also takes part in the ab- 

 sorption of the albumen. 



The fusion of the allantoic mesoderm and blood vessels 



