OCTOMITUS SALMONIS, A PARASITIC FLAGELLATE OF TROUT 
13 
While a ridge can sometimes be seen on one side of the body, this is evidently due 
to a temporary displacement of the axostyles. 
Attached to the anterior end are three pairs of flagella, which vary considerably 
in length but are usually about one and one-half times the length of the body. 
These flagella arise from the blepharoplast complex attached to the anterior ends 
of the axostyles. Surrounding the base of each flagellum is a deeply staining layer, 
which extends from the axostyles to the point at which the flagellum leaves the 
body (figs. 4, 6, and 8). Owing to this layer, it is often very difficult, if not 
impossible, to distinguish a definite granule at the base of the flagella, and one gets 
the impression that the blepharoplast complex is formed by the greater development 
of the deeply staining layer at the junction of flagella and axostyles. A fourth 
pair of flagella arise from the axostyles at the extreme posterior end of the body. 
These flagella are considerably longer than those at the anterior end and trail 
behind the animal when it is in motion. 
The axostyles are a pair of slender flexible rods which extend the entire length 
of the body &nd can usually be distinguished in the living animal. Their relative 
position is very variable, and while they may sometimes lie nearly parallel (figs. 
1 and 2) they often extend across each other as shown in Figure 3. At the anterior 
end the axostyles are surrounded by a chromatic layer which in deeply stained 
specimens may be conspicuous (fig. 5), but is usually indistinguishable in strongly 
decolorized individuals. Near the posterior end is a characteristic structure, also 
composed of chromatic material, which is easily recognized even in strongly 
decolorized individuals. This structure appears as three or four granular chromatic 
bands extending along the axostyles for about one-third their length (figs. 1 
to 5). These bands often appear to form the walls of a pair of longitudinal grooves 
and were so described by Moore (1922). However, when viewed from the posterior 
end (fig. 7) it is evident that the chromatic material in reality forms a pair of funnel- 
shaped structures attached to the axostyles with the smaller end pointed forward. 
Owing to the movements of the axostyles, the appearance of these structures varies 
greatly in different individuals. 
At the anterior end of the body is a pair of ovoidal or egg-shaped nuclei, with 
the smaller end extending anteriorly to connect with the blepharoplast complex 
and axostyles. Surrounding the nucleus is a delicate membrane, within which a 
layer of chromatic granules can be seen in deeply stained individuals (fig. 5), but 
these readily lose the stain when the preparations are properly decolorized. Within 
the nucleus is a central karyosome surrounded by a clear space or halo. The karyo- 
some is elongated and stains deeply with hematoxylin. When properly decolorized 
it can be seen to be composed of deeply stained granules embedded in a lighter 
matrix — the plastin — which extends anteriorly to connect with the blepharoplast. 
In strongly decolorized individuals the chromatic material is limited to a single 
spherical granule near the middle of the karyosome (figs. 4 and 6). When further 
decolorized, this chromatic body gradually grows smaller and eventually disappears. 
There can often be seen, near the middle of the body, a pair of irregular, finely 
granular structures, which stain somewhat darker than the surrounding cytoplasm 
(figs. 1 and 2). These structures vary greatly in shape and appearance, and, while 
