SCHIZAMCEBA SABMONIS 
3 
appear to be dividing by amitosis. That mititic division does not occur in the ame- 
boid stage is also indicated by the fact that a careful search has failed to disclose 
any evidence of mitosis at this stage. This agrees with the observations of Taylor 
(1923), who was unable to find any evidence of mitotic division in the ameboid 
stage of Amoeba proteus. 
STRUCTURE OF CYSTS 
Usually, in addition to the ameboid stages just described, there are numerou 
cysts present in the stomach which have a quite different appearance. These cysts 
are often more abundant than the vegetative stages, which in several instances 
were rare while the former were present in large numbers. On the other hand, the 
opposite condition may obtain, and in one noteworthy case very few cysts were 
found, although the ameboid stages were extremely abundant. This would indicate 
that cyst formation is more rapid at certain times than at others, although little 
evidence has been obtained regarding the factors controlling their development. 
The facts at hand indicate that cyst formation may possibly be correlated in some 
way with the amount of food in the stomach of the host. 
The cysts are spherical and vary greatly in size, the diameter usually being be- 
tween 15 and 35 microns, with an average diameter of 20 to 25 microns. They are 
surrounded by a thin transparent membrane and usually contain numerous spherical 
refringent bodies, which are evidently fat globules since they stain deeply with 
Sudan III and are unaffected by iodine. No glycogen vacuoles could be demon- 
strated, but since the inner half of the cysts usually stains deeply with iodine it is 
believed that glycogen is present in a diffused condition. In a few instances small 
irregular bodies staining deeply with iodine could be distinguished near the center 
of the cyst. After being on the slide for some time the fat globules may be squeezed 
out of the cytoplasm and coalesce to form a large globule in the space between it 
and the cyst wall. 
A study of stained preparations shows that the cysts are always multinucleate, 
containing from three up to a large number of nuclei (figs. 20 to 22). The structure 
of the nuclei is very different from that of the vegetative stages, and were it not for 
the fact that a complete series of transition stages can be found between the two 
forms it would be difficult to believe that they belong to the same species. In striking 
contrast to the ameboid forms the cyst nuclei always contain a large deeply-staining 
karyosome near the center, while the nuclear wall is entirely free from chromatic 
material (fig. 20). The karyosome usually stains intensely and uniformly with 
chromatin stains, but in a few strongly decolorized specimens could be seen to be 
composed of closely crowded chromatic granules embedded in a lighter staining 
matrix. On one side of the karyosome, usually that turned toward the periphery of 
the cyst, is a mass of achromatic material extending from the karyosome to the 
nuclear wall. It does not, however, extend directly to the wall, but flares out in all 
directions a short distance from the karyosome to form a mushroom-shaped struc- 
ture with its edges in contact with the nuclear membrane (fig. 20). Embedded in 
the achromatic material are numerous small deeply-staining granules, whose later 
history indicates that some of them, at least, are to be considered as homologous 
