BLOOD AND BONE-MARROW OF FROG 455 
other amphibia, including the frog, lose their azurophil (i.e., 
neutrophilic, metachromatic) granules when they differentiate 
into polymorphonuclears, and maintains that the cytoplasm of 
' the definitive polymorphs of these forms is oxyphilic. Neu- 
mann!’ likewise denies the presence of granules in the poly- 
morphonuclear leucocytes of the frog. However, my prepara- 
tions of frog marrow very clearly show that the neutrophilic 
myelocytes retain and increase their ‘azurophil’ granules as they 
differentiate into the definitive forms of the circulating blood. 
Downey* states further that all possible intermediate stages 
between larger lymphocytes (with neutrophilic granules) and 
neutrophilic polymorphs occur in the circulating blood of Am- 
blystoma. This finding is at variance with that of Maximow"™ 
in the case of Axolotl. 
In view of the fact that the complete developmental history 
of the polymorphonucleated neutrophilic leucocytes from non- 
granular basophilic primitive lymphocytes can be traced in the 
sections of the red marrow, Downey’s interpretation of transition 
forms between ‘definitive’ lymphocytes and neutrophilic granu- 
locytes in the circulation of Amblystoma at first seems quite 
improbable. The nucleus of the circulatory lymphocytes is 
very different from that of the medullary lymphocytes (compare 
figs. 4 dnd 37), a change which indicates progressive differentia- 
tion. However, a careful study of the different types of circula- 
tory lymphocytes in the frog forces the conclusion that these 
lymphocytes do actually metamorphose into the neutrophilic 
granulocytes, as urged by Downey* for Amblystoma, but denied 
for the frog. Moreover, the nuclei of the medullary and circu- 
latory neutrophils and of the circulatory lymphocytes are prac- 
tically identical in their fundamental features. It would seem 
that a lymphocyte with an already considerably differentiated 
nucleus may develop neutrophilic granules abundantly and so 
pass over into a neutrophilic granulocyte whose nucleus may 
subsequently undergo lobulation. Such a developmental proc- 
ess is illustrated in figures 8, 13, 16, and 19. 
Figure 8 is a typical lymphocyte with a reniform nucleus. 
The only perceptible cytoplasmic difference between it and a 
