PLATE 5 



EXPLANATION OF FIGURES 



10 Vasofactive cell with three nuclei. The nucleus at the right has original 

 mesenchymal features; the endothelial 'cell' below the lumen has assumed hemo- 

 blast features, and has differentiated an intracellular erythroplastid (ep). 

 Figures 10 to 15 are magnified 1500 diameters. 



11 Vasofactive cell differentiating a lumen. This figure corresponds to a 

 transverse section of figure 10. 



12 and 13 Vasofactive cells with an erythroplastid in the lumen. 



14 Vasofactive cell in early stage of differentiation from mesenchyme. The 

 cell has in general hemoblast features. The larger nucleus has produced a small 

 bud at the left. From such nuclear buds and their enveloping cytoplasm 

 develop intracellular erythroplastids. 



15 (a to i) Vasofactive mesenchymal cells at various stages of differentiation: 

 a) Typical young erythroblast ('megaloblast'). h) Hemoblast that has differ- 

 entiated an erythrocyte intracellularly. c) Cell with vascular lumen and an 

 intracellularly differentiated erythroplastid. d) Cell with lumen, having as- 

 sumed endothelial features, e) Cell with lumen, containing an . erythrocyte 

 (ec, 'normoblast') and an erythroplastid (ep.). f) Binucleated cell with two 

 intracellularly differentiated erythroplastids (ep). g) Cell with lumen and two 

 nuclei, both with endothelial features, h) Cell with four nuclei, one apparently 

 in process of amitotic division. The centrally located nuclei with their en- 

 veloping cytoplasm may differentiate into erythrocytes. ?') Binucleated cell, 

 endothelial in character, with lumen containing an erythroplastid. 



26 



