c /it 



Fig. 43 Section through an anterior body region of a four-day embryo with- 

 out a circulation; Experiment 11, 1912, Embryo 6. The dorsal aortae, DA, 

 are seen lined by typical embryonic endothelium, yet they are throughout com- 

 pletely empty, never containing blood cells. 



Fig. 44 A section through the cardial vein of a similar four-day embryo 

 without a circulation; Experiment 11, 1912, Embryo 4. Again the embryonic 

 endothelium, Et, is well formed but the lumen of the vessel is packed with ery- 

 throblasts; EC, ectoderm; Afes, mesenchyme; En, entoderm. 



53 



