4 
BULLETIN OF THE BUREAU OF FISHERIES 
with the centrioles and blepharoplasts of other protozoa. That they differ chemically 
from the chromatin of the karyosome is indicated by the fact that in very strongly 
decolorized nuclei they are unstained while the karyosomes still retain the stain. In 
fact, the appearance and abundance of these granules appears to be largely de- 
pendent on the stage to which the destaining process has been carried. 
The arrangement of the nuclei in the cyst is characteristic. Except in the case 
of the small cysts with few nuclei they are usually arranged quite regularly in a single 
layer about one-half the distance from the center to the periphery of the cyst (figs, 
20 and 22). This arrangement divides the cytoplasm into two regions, which 
present a quite different appearance. Within the nuclear layer the cytoplasm is 
strongly vacuolated, while in the outer zone between the nuclear layer and the 
periphery the vacuolated structure is much less noticeable and in the larger cysts 
may entirely disappear. 
In some instances a mass of deeply staining granules is present at one side of 
the cyst, which is probably homologous with the chromatoidal structures of other 
amebae, but in the great majority of cysts no trace of such a structure can be dis- 
inguished. The explanation of this fact is not obvious, since it can hardly be due 
to differences in fixation or staining. 
DEVELOPMENT OF CYSTS 
Perhaps one of the most interesting features in the life cycle of this species is 
to be found in the development of the cysts from the ameboid stage, since the 
process is quite different from that described for other amebae. As previously 
noted, the nuclei of the amebae frequently exhibit a quite different arrangement of 
the chromatin from that usually found. Instead of forming a thin layer, either 
continuous or composed of discrete granules on the inside of the nuclear membrane, 
the chromatin becomes arranged in large blobs, as shown in Figures 3 and 10 to 13. 
There are usually five or six of these chromatin masses in each nucleus, but the 
number is by no means constant. This arrangement of the chromatin is apparently 
the first step in cyst formation and may occur in both mononucleate and multi- 
nucleate individuals. Judging from their abundance, this stage lasts for some time, 
and the nuclei may even divide amitotically while in this condition. After a time 
the chromatic masses become rounded and usually exhibit a vesicular structure 
(figs. 14 to 17), the chromatin forming a peripheral layer around the less deeply 
staining center. 1 At this time the nuclear wall shows signs of disintegration and 
a little later entirely breaks down, leaving the chromatin spherules free in the 
cytoplasm (figs. 18j_and 19). These spherules form the karyosomes of the cyst 
nuclei, losing their vesicular structure and each becoming surrounded by a nuclear 
membrane. 
The nuclear changes involved in the development of the cysts are accompanied 
by corresponding changes in the cytoplasm. The organisms become rounded and 
are surrounded by a thin transparent membrane which is difficult to distinguish 
in stained specimens. The cytoplasm is distinctly vacuolated and contains numer- 
1 The vesicular structure is evident only in stroDgly decolorized individuals 
