OCTOMITUS SALMONIS, A PARASITIC FLAGELLATE OF TROUT 
17 
cociously in advance of the division of the cells, which occurs somewhat later. At 
this stage the organism is usually somewhat elongated, with the nucleus at one end 
(fig. 31). Occasionally the host cell may disintegrate at this stage, the parasite 
passing into the intestinal lumen. In such cases it is apparently unable to complete 
its development, since, although this stage of the organism is sometimes not uncom- 
mon in the intestine, they invariably appear to be in a moribund condition and later 
stages have not been found. 
Division of the full-grown parasite or schizont is accomplished by a very primi- 
tive form of mitosis shown in Figures 33 to 36, but which is very difficult to follow in 
detail. The daughter cells formed by this division (figs. 37 and 38) are unsym- 
metrical, and instead of lying side by side, as in ordinary division, one is partially 
inclosed by the other. This peculiar relation of the two cells is very characteristic; 
sometimes the outer cell is much flattened and almost entirely incloses the other. 
Often the nucleus of the enveloping cell has a quite different structure from that of 
the inner cell (figs. 39 and 40), and in some cases, at least, this cell may eventually 
degenerate. Several divisions of the inner cells follow in rapid succession until as a 
result of this process numbers of small spores or merozoites are formed (figs. 41 to 
47), which then make their way into uninfected cells and repeat the cycle. As 
stated above, the enveloping cell often degenerates during the process of schizogony, 
but whether this is always the case is uncertain. In Figures 43 and 44 it is very 
evident that the cell is gradually distintegrating, but in many other instances, such 
as shown in Figure 41, no trace of a degenerating cell could be found. There appears 
to be considerable variation in the behavior of the cells during schizogony, and it is 
probable that many of the parasites are destroyed during the process. In many 
cases entire groups of cells in various stages of schizogony do not stain normally and 
are apparently moribund. In fact, the whole process gives one the impression that 
in this species the intracellular cycle is a comparatively recent development and that 
the organism has not yet become completely adjusted to such an environment. 
It is obvious that schizogony furnishes a rapid means of multiplication, since 
the entire process requires but a short time, probably not more than 24 to 48 hours 
under favorable conditions. It has often been noticed that infection of the epithe- 
lial cells is not uniform but that here and there are groups of cells in which nearly 
every one is infected, while between such areas there may be only an occasional 
infected cell. Such a condition is evidently due to infection by merozoites that 
invade the surrounding epithelium, causing an intensive infestation of the cells in the 
immediate vicinity and in many cases the complete destruction of the epithelium. 
In addition to the stages just described, other intracellular forms are some- 
times met with which do not fit into the cycle of schizogonous development. A 
number of these forms are shown in Figures 48 to 56. It is evident that this series 
shows a gradual transition from the typical intracellular parasite to the flagellated 
form in the lumen of the intestine. In the early stages these cells differ from 
those previously described only in the fact that nearly all the chromatin is col- 
lected in two large masses on opposite sides of the nucleus (figs. 48 and 49) instead 
of being uniformly distributed, as in the majority of parasites at this stage. How- 
ever, the writer is by no means convinced that all cells showing such an aggrega- 
