THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



241 



red corpuscles. The parent stem cells, here called myeloblasts, are recog- 

 nizable in the form of large mononuclear, non-granular cells, with the general 

 characters of primitive lymphocytes, which give rise to the red blood cells 

 through clearly distinguishable megaloblast and normoblast stages, and to 

 the various forms of leucocytes and lymphocytes. In addition the parent 



W 



m 



f' 



/W 

 /// 



tn 



** 



'"?? 4tt -* 



^ V 



^m-- 



m ^ 



^j 



~ && i 



m 1 



meg 

 m 



I 



' 

 / 



e' 



m 

 /re' 



/n" 



FIG. 212. From a section of red marrow from the femur of a young rabbit. Schafer. 

 e, Erythrocy tes ; e r , normoblasts; e", normoblast in mitosis; /, outlines of fat cells; ^, polymor- 

 phonuclear leucocytes; m, neutroohile myelocytes; m', myelocytes in mitosis; m", 

 eosinophile myelocytes; m'". basophile myelocytes. 



cells also give rise to certain other cells which are normally confined to the 

 marrow, viz., the myelocytes. These are large mononuclear cells, with 

 vesicular nuclei, the cytoplasm containing neutrophile, acidophile, or baso- 

 phile granules similar to those of the leucocyte series (Fig. 212). The 

 genetic relationships of the "giant" cells, or myeloplaxes, in the marrow are 

 not clear. The myeloplaxes are large masses (30 to 100 micra in diameter) 



