PLATE 2 



EXPLANATiOX OF FIGURES 



4 From a section of a chick embryo of o (lays, 12 mm. (series no. 336; slide 

 IV, section?). Photomicrosi'aph, X 166. 



1, aorta 10, preeardinal vein 



3, aortic arch VI 16, grouj) of developing blood cells 



4, aortic arch 1\ 



5 From a section of a cfiick embryo of 6 days, 13.5 mm. (series no. 339; 

 slide VIII, section 35). Photomicrojirajjh, X 166. 



2, dorsal aortic root 16, groups of developing blood cells 



3, aortic arch VI 27. vagus nerve 



166 



