6 
BULLETIN OF THE BUREAU OF FISHERIES 
appears strikingly like the granules embedded in the achromatic structure joining 
the karyosome to the nuclear wall in S. salmonis. However, it is very evident 
that in salmonis these granules take no part in the formation of the chromosomes 
hut become arranged at the poles of the spindle during the prophase. In this 
respect they would appear to correspond with the chromatic polar masses, which 
in Amoeba tachypodia and Nxgleria gruberi are derived from the karyosome. Ob- 
viously, further investigations are required before it will be possible to determine 
the homologies of the nuclear structures in the two types of amebae. 
Coincident with the division of the nuclei there is a marked increase in the 
size of the cysts, which may eventually reach a diameter of 35 microns and contain 
a large number of nuclei. Occasionally a large cyst is found in which the nuclei, 
instead of being distributed quite regularly around the central portion of the cyst, 
as previously described, are arranged in several groups separated a short distance 
from each other. This arrangement of the nuclei is preparatory to division of the 
cyst into a number of distinct parts corresponding to the number of nuclear groups. 
Superficially this division has a striking resemblance to the segmentation of an egg 
hut differs in several fundamental respects. Unlike an egg, the cyst divides simul- 
taneously into from 4 to 11 cells of approximately equal size (figs. 36 and 37) 
Each cell usually contains from 4 to 8 nuclei, there being considerable variation in 
this respect even in daughter cells from the same cyst. The disintegration of the 
cyst membrane, which quickly follows, allows the cells to separate, and presumably 
each in turn may go through a similar course of development. Dividing cysts, 
while not common, have been found in a number of instances in both the stomach 
and intestine, and there can be no doubt that this is a normal process in the life 
cycle of the species. 
The further development of the cysts has not been followed, but it is known 
that they pass out of the intestine in the excrement in the condition shown in 
Figures 20 and 22, and presumably germinate after being ingested by another fish. 
SYSTEMATIC RELATIONSHIP 
It is evident that this ameba differs in several essential respects from other 
known species. The most striking differences are found in the encysted stage, 
and these are believed to be of sufficient importance to justify the creation of a new 
genus coordinate with other genera of the Amoebidae. The essential characters 
of this genus are as follows : 
Schizamoeba gen. nov. 
Parasitic. Trophozoites mononucleate and multinucleate. Cyst nuclei formed 
by fragmentation of nuclei of trophozoite, with large central karyosome connected 
at one side with the nuclear membrane by an achromatic structure in which are 
embedded numerous chromatic granules. Cysts divide into a number of multi- 
nucleate cells, each of which forms a separate cyst. 
Type species Schizamoeba salmonis sp. nov. 
Trophozoite slowly ameboid, with one to several vesicular nuclei without a 
karyosome, and with the chromatin arranged on the nuclear wall. During encyst- 
