10 H. E. JORDAN 



cell, young endothelial cell, hemoblast, erythroblast ('megalo- 

 blast'), and the erythrocyte. The mesenchymal cell has in 

 general a light-staining, spheroidal or oval nucleus with a delicate 

 reticulum; its cytoplasm contains delicate fibrillae. The young 

 endothelial cell has a similarly light-staining, but generally more 

 elongated nucleus; and its cytoplasm is less distinctly fibrillar. 

 The hemoblast is generally spheroidal in shape, but it may 

 assume various forms due to its ameboid capacity; its nucleus 

 also generally has a spheroidal shape, but it contains a more 

 distinct and more granular network, and the cytoplasm appears 

 homogeneous. The nucleus of the young erythroblast ('megalo- 

 blast') has a spheroidal shape, a robust chromatic membrane, a 

 generally deeper-staining nucleoplasm; and it contains one or 

 several small nucleoli and numerous granules scattered over its 

 delicate reticulum. Its cytoplasm is distinctly granular, and 

 it stains deeply in eosin. The granular condition of the cyto- 

 plasm of the erythroblast is the most distinctive mark of this 

 cell. This cell corresponds to the megaloblast of certain writers. 

 The erythrocyte has a considerably smaller, generally deeper- 

 staining, spherical nucleus, and a clear cytoplasm delimited by 

 a distinct membrane (figs. 6, e, and 15,6 ande). Theerythro- 

 plastid has in contrast a brownish-yellow color. 



In figure 15 (a to i) are illustrated various vasofactive and 

 hemogenic cells. In fact, as these figures clearly indicate, vaso- 

 factive and hemogenic activities are intimately associated. The 

 cell a may be regarded as at the stage of a late hemoblast or a 

 young erythroblast. The cell b is similar, but has produced an 

 intracellular erythrocyte. Cell c has developed a lumen, and 

 it has differentiated an inclosed erythroplastid. Cell d is es- 

 sentially a young endothelial cell with vestiges of cytoplasmic 

 hemoblast features. Cell e has become essentially a young 

 endothelial cell with an included small erythrocyte and an 

 erythroplastid. Cells g and i are essentially hemoblasts ('angio- 

 blasts') which have become differentiated into binucleated 

 endothelial cells. Cells/ and h should be interpreted together; 

 h is essentially a multinucleated hemoblast or small 'giant-cell/ 

 one of whose nuclei is apparently undergoing amitotic division; 



