PLATE 1 
EXPLANATION OF FIGURES 
All the figures, with the exception of 13, 25, 26, and 27, were drawn from sec- 
tions of the femoral red bone-marrow of the rabbit; fixed with Helly’s fluid, cut 
at 5 w and stained with iron-hematoxylin. The original magnification was 1600 
diameters; this was reduced 3 in reproduction. 
1 Young megakaryocyte. It has the nuclear and cytoplasmic characteris- 
tics of a large hemoblast. 
2 Older and larger megakaryocyte, with more deeply staining crescentic 
nucleus. It corresponds to a simpler variety of polymorphokaryocyte. 
3 Later polymorphokaryocyte with lobulated ‘basket’ nucleus. In the cyto- 
plasm included within the annular nucleus (as it appears in section) hes a group 
of centrosomes. 
4 Polykaryocyte. The cytoplasmic area bounded by the ring of discrete 
nuclei contains a collection of centrosomes (pluricorpuscular centrosome). 
5 Beginning of disintegration of a polykaryocyte. The chromatin of each of 
the five nuclei has gathered into peripheral droplets, simulating chromosomes 
arranged in equatorial plates. At the left two groups are mingling. Neither 
centrosomes nor spindler fibers are discernible. 
6 Later stage in disintegration. The chromatin masses, still simulating 
chromosomes, are indiscriminately mingled. 
7 Polymorphokaryocyte, similar to that of figure 2. This corresponds to 
stage 3 of the mitotic division of these giant-cells as interpreted by Dickson. 
8 A variety of polymorphokaryocyte. The area inclosed by the nucleus con- 
tains scattered centrosomes. This corresponds to stage 4 of mitosis, according 
to Dickson. At the right the cytoplasm has been invaded by an eosinophilic 
granulocyte. 
9 Polymorphokaryocyte in process of becoming a polykaryocyte. Three 
smaller spherical nuclei have already separated from the main nuclear mass. 
Two of the separated nuclei (a and c) have the characteristics of nuclei of erythro- 
blasts. Nucleus c is actually enveloped by a distinct shell of cytoplasm which 
has separated from the cytoplasm of the giant-cell; and the resulting cell con- 
stitutes an erythroblast differentiated intracellularly from the giant-cell. 
10 A variety of polymorphokaryocyte. This is very similar to stage 5 in 
mitosis, according to Dickson. 
11 Early stage in the disintegration of the foregoing variety of polymorpho- 
karyocyte. The lobulated nucleus appears to have drawn in its longer extensions 
and become massed into a simpler, more compact, structure with extremely 
irregular and chromatic contour. The chromatin has collected in droplets, rods, 
and strands simulating a segmenting spireme. 
12 Later stage in the process of this mode of disintegration. The nuclear 
chromatin has become arranged into a structure simulating a prophase spireme. 
This condition may follow that of figure 10 without the intervening stage of 
figure 11. 
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