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 verj^ 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 mesenchj-mal 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. 



149 



