BLOOD AND BONE-MARROW OF FROG 463 
they are present only in the mast-cells. However, I find abun- 
dant examples of just such cells as depicted by Downey in sec- 
tions of young turtle embryos in the periaortic connective tissue. 
It must be emphasized that the fixing and staining fluids in 
these instances. (turtle embryo, Jordan; guinea-pig, Downey) 
were the same, namely, Helly’s fluid followed by the Giemsa 
stain (Downey employed also other similar stains but not 
Wright’s combination). In the case of the frog’s marrow the 
fixation was secured with a corrosive-sublimate-formalin mixture 
and the staining was done with Wright’s stain. It seems prob- 
able that a difference of appearance, as concerns presence or 
absence. of blue-staining granules among the red granules in 
eosinophilic myelocytes depends upon the type of fixing fluid and 
staining combinations employed. In the frog material under 
consideration, it can only be said that less oxyphilic granules 
precede more oxyphilic granules, and that the former are always 
smaller than the latter. 
All the evidence in this material, moreover, clearly points to a 
heteroplastic origin of these cells from lymphocyte ancestors, 
and the endogenous origin of the eosinophilic granules. Only 
the younger types of myelocyte, i.e., with non-polymorphous 
nucleus, are capable of mitotic division and thus of forming new 
eosinophilic myelocytes. The granules are in no case ingestion 
products of hemoglobin-containing fragments of disintegrating 
erythrocytes, but result from the specific activity of the myelo- 
cyte protoplasm. Moreover, the nucleus is never invaded by 
these cytoplasmic granules, as maintained by Niegolewski,'* nor 
is there the slightest evidence in support of Weidenreich’s* 
theory that eosinophilic granules are the ingested fragmenta- 
tion products of erythrocytes. In this material the erythrocytes 
develop only intravascularly, where they also fragment; the 
eosinophils, on the other hand, develop only extravascularly. 
All the evidence inclines towards the interpretation of these 
granules as the product of a specific cytoplasmic activity. 
The chief question regarding the basophilic leucocytes (mast- 
cells) is whether they represent a specific type of normal blood- 
cell or whether they represent degenerations of lymphocytes or 
