HISTOGENESIS OF BLOOD IN BUFO HALOPHILUS 219 



Now as to the erythrocytoid differentiation of the primitive 

 blood-cells. The nucleus retains its round or oval shape and its 

 definite nuclear membrane, which may be indented by a single 

 remaining yolk granule. The chromatin becomes much more 

 abundant, condensing to form a heavy network. At this stage 

 the nucleolus reacts to basic stains in practically the same manner 

 as the chromatin of the nucleus, and as the denser network of 

 the latter develops, the nucleolus gradually loses its identity and 

 becomes merged in the common chromatin content of the nucleus. 

 The exact time of its disappearance is somewhat variable, in 

 some cases the nucleolus persisting almost up to the first 

 appearance of hemoglobin. The karyoplasm retains its faintly 

 oxyphil character as long as it is at all distinguishable in the 

 increasing density of the nucleus. This forms one of the distinct 

 differences between the early erythroblasts and the large lympho- 

 cytes. As the yolk disappears from the cytoplasm, the latter 

 takes on an increasingly basophil reaction, varying somewhat in 

 intensity in different cells. With the appearance of hemoglobin 

 this blue color soon shows a gray tint tending either toward green- 

 ish or purplish, depending on whether the developing hemoglobin 

 takes a yellow or a pink stain with eosin-azure II. The cytoplasm 

 becomes much vacuolated, these vacuoles persisting some little 

 time after the disappearance of the yolk. The cells are oval, 

 but not yet flattened, with sharply defined, smooth contours 

 which are not necessarily perfectly uniform, but do not present 

 any evidence of amoeboid activity. 



The second type of cell differentiating from the primitive 

 blood-cell is the large lymphocyte (fig. 3, Lib, Lie). In this 

 process the cytoplasm of the former becomes very strongly 

 basophil with the decrease of its food yolk. The cell outline 

 shows strongly marked evidence of amoeboid activity. The 

 cytoplasm of the large lymphocyte is broad, has no definite cell 

 membrane, and appears reticular in some cells, in others hyaline. 

 The nucleus is round, oval, or slightly indented, the indentation 

 frequently facing the remaining yolk, and central or excentric in 

 position. The karyoplasm becomes typically clear and colorless. 

 The chromatin decreases in amount and is disposed in irregularly 



