Fig. 31 A group of six early erythroblasts unsurrounded by endothelium 

 on the yolk-sac of a 90 hour embryo. Short amoeboid processes project and the 

 cells move very slowly. 



Fig. 32 A camera lucida sketch of a microscopic field on the yolk-sac of a 90 

 hour embryo. All four derivatives of the wandering mesenchymal cells are 

 shown. The circulation is established in the vessel to the right and the current 

 follows the direction of the arrows. To the left is a small vessel not yet connected 

 with the current; its wandering endothelial tip is approaching a group of 

 erythroblasts still uninclosed by endothelium as they lie near the huge black 

 chromatophore. A brown chromatophore is seen on the large vessel. 



569 



