456 H. E. JORDAN 
lymphocyte like that illustrated in figure 6 pertains to the 
relative proportion of neutrophilic and basophilic granules. The 
designation ‘basophilic granules’ in connection with lymphocytes 
is always used here with the reservation that the ‘granules’ may 
be actually a coagulation phenomenon in an essentially homoge- 
neous cytoplasm. Certain circulatory lymphocytes contain only 
a few neutrophilic granules; these types lead through transition 
forms to neutrophilic granulocytes which show many granules and 
interspersed small areas of only basophilic granular material. 
The conclusion seems inescapable that lymphocytes may, and 
continually do, differentiate into polymorphonucleated neutro- 
philic granulocytes within the circulation. This would seem to 
dispose of Werzberg’s” classification of the lymphocytes of frog 
as nongranular large and small lymphocytes, ‘leucocytoid lym- 
phocytes with azurophil granulation,’ and ‘lympholeucocytes.’ 
In the frog the lymphocytes differ in their cytoplasmic features 
only in respect of the relative abundance of neutrophilic (azuro- 
phil) granules. This conclusion has an important bearing upon 
the discussion regarding the validity of the monophyletic the- 
ory of hemopoiesis. The circulatory lymphocyte, the slightly 
modified persistent medullary lymphocyte which functions as 
the common progenitor (hemoblast) of all types of blood-cells, 
still maintains its capacity to differentiate at least into a neutro- 
philic granulocyte. 
The question then arises whether the Amphibian neutrophils 
are actually the homologues of the mammalian megakaryocytes 
or of the mammalian polymorph neutrophils. If these cells are 
regarded as representing polymorph neutrophils of higher mam- 
mals, then amphibian blood, except for thrombocytes, would 
seem much closer to mammalian than to sauropsid bloods. This 
would conflict with the accepted phylogenetic seriation. How- 
ever, neither neutrophilic leucocytes nor recognized hemogenic 
giant-cells occur in sauropsid marrows, while leucocytes with 
‘special’ (eosinophilic, ellipsoidal) granules are abundant, facts 
which favor Downey’s® interpretation. The evidence seems to 
point to the homology of the amphibian and mammalian poly- 
morph neutrophils. Whether both are the homologues of the 
