HISTOGENESIS OF BLOOD IN BUFO HALOPHILUS 221 



THE FURTHER DIFFERENTIATION OF THE PRIMITIVE 

 ERYTHROCYTE STEM 



At the end of the last stage, 6 mm., the primitive erythroblast 

 is a large, ellipsoidal, vacuolated cell with a large, round or oval, 

 chromatin-rich nucleus. This cell is not at all flattened, but is 

 somewhat irregular in contour. With eosin-azure II its cyto- 

 plasm stains a light blue with no trace of pink. 



Between 6- and 6.5-mm. body length hemoglobin first appears, 

 the cytoplasm now taking on a pink stain with triacid. With 

 eosin-azure II some cells may now show a greenish-gray color, 

 some a pink tint, but many are still pure blue. They are begin- 

 ning to flatten, but a considerable margin of cytoplasm still shows 

 on all sides of the nucleus. This body uniformly appears darker 

 than the cytoplasm and contains much more chromatin than 

 that of the lymphoid type. The erythroblasts now far out- 

 number the lymphocytes in the heart blood and frequently 

 present mitotic figures. 



Between 6.5- and 7-mm. body length the erythroblasts rapidly 

 approach the definitive form (fig. 4, p.eb) of the adult erythrocyte, 

 there being now very little cytoplasm between the nucleus and 

 the flattened sides of the cell. With eosin-azure II the cytoplasm 

 is of a gray color with elements of both blue and pink visible. 

 The pink is more pronounced in some cells than in others, and 

 is determined by the increased development of hemoglobin in 

 their cytoplasm. Many vacuoles still remain, disappearing last 

 from near the nucleus. A cell containing a single yolk granule 

 may still be met with occasionally. 



From the 7-mm. stage on the majority of the cells, and soon 

 all of them, are oxyphil, hemoglobin-carrying primitive erythro- 

 cytes. Through all the stages studied, up to 38-mm. body 

 length, no definitive erythropoiesis was observed. Mietens ('10) 

 states that in Bufo vulgaris definitive erythropoiesis does not set 

 in until the time of the metamorphosis. 



At the 8-mm. stage the primitive erythrocytes (fig. 5, p.ec) are 

 pink stained, hemoglobin-containing, oval, flattened, biconvex, 

 sharp-bordered discs with a spherical, flattened, or oval chrom- 

 atin-rich nucleus, showing an indistinct chromatin network. 



