BLOOD AND BONE-MARROW OF FROG 467 
centrosomes is related to the high stage of differentiation as 
expressed fundamentally in the neutrophilic granules. This 
suggestion is in harmony with the facts that the later eosino- 
philic myelocytes, the basophilic myelocytes, the thrombocytes, 
and the giant-cells also do not divide mitotically. All of these 
cells express in their peculiar cytoplasmic condition a high degree 
of differentiation. The reason for the failure of basophilic 
myelocytes, thrombocytes, and giant-cells fot the most part, 
to proliferate even amitotically is under this view not clear. 
However, if we assume that the lobulated nucleus of the neutro- 
philic myelocytes represents an unfinished amitosis, then pos- 
sibly the bilobed nucleus of the basophilic myelocytes, the deeply 
grooved condition of the thrombocyte nucleus, and the poly- 
morphous character of the giant-cell nucleus (in mammals) may 
legitimately be similarly interpreted. 
The nuclear amitosis of the neutrophilic myelocytes and the 
amitosis of the hemoblasts (large lymphocytes and erythroblasts) 
are apparently similar phenomena resulting from quite different 
causes— cytoplasmic specificity or high differentiation and intense 
proliferative demands, respectively. These dissimilar causative 
-factors may, however, be brought under a common head 
as regards their effect on the potency and integrity of the 
kinetic center, the centrosome. Both conditions may be con- 
ceived to reduce relative nutritive conditions below the possi- 
ble minimum for centrosomal activity. In essence, amitotic 
proliferation, in contrast with mitotic proliferation, results 
presumably when the metabolic demands of the protoplasmic 
mechanism are such as to deprive the astral system of its 
minimum nutritive requirements. This assumption can at 
least harmonize the apparently contradictory facts that amitosis 
occurs in the cells of rapidly growing tissues as well as in highly 
specialized and degenerating cells, an idea first suggested by 
Child.! 
In this connection attention must again be directed to the two 
main types of astral systems in the neutrophilic granulocytes: 
one clear with a central monosome or diplosome, the other con- 
sisting of a larger or smaller granular sphere. As described 
