PLATE 3 



EXPLANATION OF FIGURES 



6 From a section of a chick embryo of 7 days (series no. 512; slide III, 

 section 15). Photomicrograph, X SO. 



2, dorsal aortic root 19, lymphatics dorsal to aortic arches 



3a, pulmonary artery and esophagus 



10, precardinal vein 27, vagus nerve 



16, groups of developing hhjod cells esophagus in center of figure 



along precardinal vein bronchi at lower border of figure 



16a, groups of developing blood cells 



dorsal to esophagus 



7 From a section of a chick embryo of 6 days and 16 hours, 13.5 mm 

 (series no. 426; slide XI, section 21). Photomicrograph, X 133. 



1, aorta 



5, celiac artery 



8, dorsal somatic artery 



16, groups of developing blood cells 



23, celom (pleural cavity) 



25, mesonephros 



26, lung anlage 



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