DE\^LOPMENT OF WANDEEING MESENCHYMAL CELLS 137 



Fig. 23 The large vitelline vein in an embrj'o of 67 hours just beginning to 

 permit the passage of blood through its lumen. Corpuscles moving in single 

 file. This becomes the largest vessel of the embryo and arose from the arrange- 

 ment of the freely wandering mesenchymal cells of figures 19, 20 and 2L In the 



