BLOOD AND BONE-MARROW OF FROG 459 
tions seem more favorable for the neutrophilic differentiation in 
the case of the majority of the lymphocytes. Eosinophilic and 
basophilic granulocytes, apparenthky differentiate only extra- 
vascularly. These enter the blood-channels secondarily through 
ameboid activity. 
Danchakoff? calls attention to an apparent contradiction in 
the argument of the supporters of the monophyletic theory of 
blood-cell origin: they note that morphologically identical mes- 
enchymal cells and hemoblasts in the same limited regions 
develop into both erythrocytes and granulocytes, and infer 
from this fact the equipotentiality of these blood-cell ancestors. 
Danchakoff argues that if these ‘stem-cells’ develop into differ- 
ent products in the same region, then they must have had dis- 
similar potentialities and were in fact originally distinct, as 
claimed by the adherents of the polyphyletic theory. But this 
argument must postulate an identity of the environmental 
factors playing upon the hemoblasts in these restricted areas; 
this involves an assumption which cannot be supported by tan- 
- gible data. It is not at all inconceivable that two adjacent, 
identically endowed, cells are nevertheless under environments 
sufficiently dissimilar to determine erythropoiesis in one case 
and granulopoiesis in the other case. It is no doubt generally 
true, as abundant recorded observations show, that hemoblasts 
enclosed by endothelium develop into erythrocytes, while ex- 
travascular hemoblasts differentiate into granulocytes. But 
Danchakoff‘ herself observed in regions in the allantois of the 
chick embryo upon which had been grafted particles of adult 
spleen, that extravascular hemoblasts could develop into eryth- 
rocytes. She, however, interprets her sections to mean that 
the extravascular hemoblasts in these instances had received an 
erythropoietic bias while previously confined by endothelium, 
which could not be reversed under the influence of the new 
environment, or that the extravascular spaces containing these 
displaced hemoblasts are actually in continuity with the orig- 
inal lumen of the blood-vessel through breaks in the endothelial 
wall. However, there are other instances in which such explana- 
tions will not suffice. For example, in the area vasculosa of the 
