4
On examining a flagellate which is about to divide longitudinally, the nucleus appears
elongated and stains more deeply ; the blepharoplast also is thickened and elongated (Figure 9).
A small pink filament is next seen lying close to the root of the flagellum from which it appears
to be entirely separate. This structure represents the early development of the second flagellum
and seemingly is formed in the same way as the original one. It soon grows out towards the
anterior end and on becoming free is intimately associated with the old flagellum. The
blepharoplast now splits transversely and the two halves separate. At the same time the
nucleus elongates and divides as described above. A clear line forms between the roots of the
flagella, the anterior ends of the parasites separate and later division extends to the posterior
ends (Figure 8). I have never observed any of these flagellates dividing unequally nor do they
appear to divide more than once, as the majority are all about the same size and extremely thin
forms were never seen.
Po s t - f l a g e l l a t e s t a g e . —On e x a m i n i n g t h e c o l o n a n d r e c t u m o f a n a d u l t b u g i n f e c t e d w i t h
Herpetomonas lygœi, it will be seen that the parasites collect in masses ; many will be found
attached in rows by their flagellar ends to the rectal epithelium. On rupturing a rectum
containing these forms it will be seen that they are of all sizes, some with and others without
flagella. All these parasites represent the various changes undergone preparatory to encyst-
ment, which I will now describe. On examining a stained preparation of these attached
flagellates, in addition to the adult forms described above, a large number will be seen
to consist of short stout parasites. Their protoplasm stains a deep blue with Giemsa and is full
of large pink staining granules (Figure 10). The nuclei and blepharoplasts of these parasites
are considerably enlarged and the flagella are often seen arising from a large achromatic area
close to the blepharoplasts. In many of the cells the flagella are quite short, only measuring
about 10 μ (Figure 11), the greater portion having been broken off. In older forms the nuclei
and blepharoplasts are seen in all stages of division, the flagella at the same time splitting into
two (Figure 12). The anterior ends of the parasites become indented and on the line of separa-
tion passing to the posterior end the parasite splits into two. At this stage the flagella often
exhibit a shredded appearance. Some of the flagella become broken off and the remainder is
represented by a few pink staining strands at the anterior end of the cell. All these appear-
ances indicate that as the flagellum degenerates it is not drawn up into the body of the parasite
but that the extra-cellular portion breaks off while the remainder degenerates and is absorbed.
The parasites now divide into two and each cell re-divides so that four oval and round bodies
are formed. These are seen lying with their anterior ends in close apposition (Figure 13) and
constitute a cyst. In the fresh condition they are seen in large numbers attached loosely to the
rectal epithelium. They can be readily recovered from the fæces of the bugs and they are the
forms which I have described above from the crops of bugs which have accidentally ingested
them (Figure 14).
The method of infection.—One of the most important points in connection with the life-
history of a parasite is to ascertain how it passes from one host to another. I have directed
special attention to this in the case of the flagellate of Lygœus militaris and although I
examined a number of infected bugs the flagellates were never found in •any other situation
than the alimentary tract. Twenty female bugs which were subsequently found to be infected
were allowed to ovulate and the eggs were transferred to a clean bottle. A large number of
these eggs were examined by smearing them out on clean slides and staining the films deeply
with giemsa, but in none of the slides could I find any parasites. Some of the eggs were kept
for six days and when the nymphs hatched out they were separated and were examined at
regular intervals. Their alimentary tracts were dissected out and examined in the fresh
condition for flagellates, after which they were smeared out and stained with giemsa. These
nymphs had descended from infected bugs and if the infection were inherited they should have
been themselves infected - but I was unable to find any parasites in their alimentary tracts. A
number of such uninfected nymphs were then placed in a bottle containing the leaves of pods
of Calotrophis gigantea on which adult bugs had been feeding. After a fortnight I found that a
large percentage of the nymphs had flagellates and developing parasites in their alimentary
tracts. If the nymphs and adults of Lygœus militaris are watched it is soon seen that while
feeding on the juice of Calotrophis gigantea they suck up the fæces which other bugs have
deposited on the leaves and pods of the plant. I frequently observed a bug actually inserting
its proboscis into fresh fluid fæces. It is therefore clear that this flagellate encysts in the
rectum of the bug, that these cysts are passed on in its excreta and the usual way the bugs
become infected is by accidentally ingesting these cysts while feeding.
THE BIOLOGICAL POSITION OF THE PARASITE.
The genus Herpetomonas, which was created by Kent in 1881 is defined as follows :—
Herpetomonas—Kent.—Flagellates which in their adult stages have a fusi form body with a
nucleus and blepharoplast. The latter is a large rod-shaped structure situated close towards the anterior
end of the parasite. Their posterior ends are nearly always pointed and may even be drawn out to a