126 FRANKLIN P. REAGAN 



III. SUMMARY 



The foregoing results furnish evidence in favor of the follow- 

 ing propositions: 



First, that mesenchyme in many regions of the body can turn 

 into endothelium, and that endothelium is not an ingrowth from 

 vessels on the yolk. 



Second, that prevascular tissue can come from more than one 

 germ-layer. 



Third, that mesenchyme cells which can form a given type of 

 blood cell are not confined to a narrowly limited region of the 

 embryo. 



Fourth, that endothelium can transform into blood-cells. 



