PLATE 5 



EXPLANATION OF FIGURES 



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

 section 1). Photomicrograph, X 233. 



1, aorta 17, lymphatics, rudiments of thoracic 



5, celiac artery duct 



16, groups of developing blood cells 23, celom (abdominal cavity) 



11 From a section of a chick embryo of 14 days (series no. 518; slide 

 XIII, section 9). Photomicrograph, X 133. 



1, aorta 17, lymphatics (part of thoracic duct 



16, blood cells, mostly mature erythro- system) 



cytes, in tissue spaces 



172 



