450 H. E. JORDAN 
However, if this nucleus were properly interpreted thus, it could 
scarcely attain a more normal appearance in the circulating 
blood. It appears that these cells undergo a further differen- 
tiation in passing from marrow to the circulation. They are the 
rarest type of leucocyte, but are most probably to be inter- 
preted as normal and specific blood elements, as maintained by 
Maximow.'® There is no evidence that the granules are nuclear 
extrusions, nor that they result from a mucoid degeneration of 
the cytoplasm. As in the case of the eosinophilic granules, they 
appear to represent the result of some metabolic activity of the 
cytoplasm. 
5. The development of the neutrophilic leucocytes. These cells 
are in certain respects the most interesting among the blood 
elements of the frog. It is only in the light of their origin in the 
marrow that their true significance can be determined. Such 
study shows that they correspond much more closely to the 
polymorph neutrophils of mammals than to the leucocytes with 
special eosinophilic granules of sauropsida, rabbit, and guinea- 
pig. They are in fact the amphibian homologues of the neutro- 
philic leucocytes of certain mammals (compare figs. 21 and 22). 
These cells alse originate from the common lymphocyte an- 
cestor (figs. 34, 35, and 54). The first indication of their differ- 
entiation is the appearance of an oxyphilic halo about the 
centrosome in the otherwise basophilic cytoplasm. This halo 
becomes finely granular and spreads in radiating fashion toward 
the periphery of the cell (fig. 54). This disposition of the neu- 
‘trophilic granules in radii is, maintained in the definitive forms 
(figs. 17 to 26). The granules vary somewhat in size and in the 
degree of their lilac coloration, but are always smaller than the 
eosinophilic granules. The basophilic substratum remains vis- 
ible, and is variably conspicuous in different regions. Coin- 
cident with the differentiation of the metachromatic granules, 
the nucleus undergoes great morphologic changes, passing ulti- 
mately into a polylobular (figs. 69 and 70), and occasionally a 
polynuclear, condition (figs. 66 to 68). Only the earliest types, 
in which the nucleus is still spheroidal or reniform (fig. 54), 
divide by mitosis. The same statement can be made for the 
