56 
Diseases of Fish 
paraffin and sectionised. Alum Haematein, followed by Picro-Sauer- 
fuchin, proved a satisfactory stain. 
Sections showed the parasite encysted between the muscle fibres 
(figs. 1 and 3). The adventitious cyst wall v/as very slight, consisting 
in places of a thin layer of connective tissue with a few leucocytes, in 
other places it appeared to be entirely absent. The parasitic cyst wall 
consisted of an extremely thin structureless layer, closely attached to 
the adventitious cyst-membrane. Within the cyst the large amoeboid 
trophozoit could be seen: this had in all cases shrunk during the 
process of fixation, and no longer completely filled the cyst. It usually 
remained attached to the cyst wall in one or more places, and in some 
cases showed processes of the protoplasm running out towards the cyst 
wall, which at first sight resembled pseudopodia. I consider that these 
are only artificially produced by shrinking due to the fixation; they 
were not seen in every cyst, but occurred occasionally with every fixative 
employed. 
The protoplasm of the trophozoit was slightly granular, and contained 
a large number of nuclei (fig. 3). Besides the normal nuclei, a number 
of pansporoblasts in various stages of spore formation were present. 
The devoloping pansporoblasts appear to migrate towards one or more 
centres in the protoplasm, with the result that one or more spherical 
masses of densely packed spores are formed, which are often visible to 
the naked eye as white opaque spots within the cysts. These masses of 
spores are surrounded by a condensation of the protoplasm, staining 
more strongly with Haematein than the remainder, and containing a 
number of small, faintly staining, elongated nuclei with an ill defined, 
reticulate, arrangement of the chromatin. In the wall of this false 
membrane, small spherical massesiconsisting of a large number of spores 
could be seen, enclosed within their pansporoblast membranes, which, 
to use Gulley’s (5) expression, are ‘subpersistent as polysporophorous 
vesicles.’ In the crowded central mass of spores the subpersistent 
pansporoblast membranes can be distinguished with a little difficulty, 
and can be seen to divide up the mass into divisions, each containing a 
large number of spores. In fig. 3 a slightly earlier stage of development 
is shown, in which a number of ‘polysporophorous vesicles’ are seen 
embedded in the central condensation of the protoplasm, which contains 
the faintly staining nuclei mentioned above. 
In addition to the nuclei already described, there were a few large, 
elongated nuclei which possessed a well-marked central mass of 
chromatin, from which strands radiated towards the nuclear membrane. 
