APPENDIX No. 2.
HERPETOMONAS LYGÆI (PATTON).
In several recent papers I have drawn attention to the close resemblance between the pre-
flagellate stages of certain Herpetomonads and the parasite of Kala-Azar.
Although all the herpetomonads already known are considerably larger than the parasite
of Kala-Azar and its two allies, the parasites of infantile splenomegaly and oriental sore, the
striking resemblance between these organisms and the three human parasites has led to my
undertaking a careful study of the life cycles of these insectan flagellates. In the present paper
I propose recording my observations on a new species of Herpetomonas. Herpetomonas lygœi
which I discovered in the alimentary tract of Lygœus militaris. This parasite, as will be seen
later, is almost identical with the parasite of Kala-Azar. For the complete description of
Herpetomonas lygœi the reader is referred to the original memoir in the Archly fur
P r o t i s t e n - k u n d e , V o l . X I I I ,p
a r t 1 , p a g e s 1 t o 1 8 .
Having made frequent investigations into the life cycles of a number of species of
Herpetomonas and Crithidia, I was able to recognise the encysted stages of Herpetomonas lygœi in
the hind-gut of Lygæus militaris, and, as in all these parasites of insects, which encyst in the
rectums of their hosts, the life eycle begins with the ingestion of the cysts, I will begin
my description of Herpetomonas lygœi at this point.
Pre-flagellate stage.—The individuals composing the cysts which are ingested by the bugs
while feeding on the juice of Calotrophis gigantea are identical with those passed out in
the fæces. They are oval, round or pear-shaped cells (Figure 1) measuring from 3. 5 μ to
4 μ in length and from 2 μ to 2 . 5 μ in breadth. The nucleus is a compact mass staining deep
pink with Giemsa's stain and measuring about 1 μ i n d i a m e t e r . I t i s o f t e n s e e n t o
con- tain. four small rod-shaped chromatic bodies. The blepharoplast, about one-third the size of the
nucleus, is almost always circular in shape and stains deep magenta with Giemsa's stain.
These forms are readily found in the white juice of Calotrophis gigantea in the crops of
the bugs.
A general enlargement of the parasite is the first stage towards development. It increases
in length and breadth and at the same time the nucleus enlarges, becomes bilobed and divides
into two—the blepharoplast thickens, elongates and splits transversely into two (Figure 2). The.
posterior end of the parasite next becomes indented, a pale area develops down the centre and
the parasite finally splits longitudinally into two cells. Each parasite immediately begins
to divide again in exactly the same manner as described above (Figure 3) and the resulting
four bodies remain attached by their anterior ends (Figure 4). In following the development
of groups of four parasites it will be seen that in nearly every group one or more of the parasites
has already flagellated while the remainder show varying gradations in size. These groups of
flagellated and non-flagellated forms remain attached together by their anterior ends and in the
fresh condition the whole group is drawn along by the adult flagellate (Figure 7j. On studying
a number of groups of parasites, many of them will be seen to have increased simultaneously- in
size, their anterior ends become elongated and rounded. Their posterior ends also soon begin
to lose their rounded shape, they elongate, and as growth proceeds each cell becomes spindle.
shaped (Figure 6).
Flagellate stage.—If a number of these parasites are deeply stained and examined with
a high magnification, in one or more a small pink area is seen lying close to the blepharoplast.
In still older specimens this area develops into a straight pink filament arising from a
point close to the blepharoplast. Later, this can be seen extending towards the anterior end of
the parasite ; it then projects from it almost symetrically, and once free, grows into a long wavy
flagellum (Figure 5). As the parasites arrive at maturity, the blepharoplasts pass down towards.
the anterior ends, the groups break up and the flagellates swim away.
A typical adult flagellate (Figure 9) measures from 20 μ to 25 μ in length and from 4 μ to.
5 in breadth. Its posterior end is pointed, its body is cylindrical and its anterior
end is rounded. The whole parasite is outlined by a distinct periplast which stains deep pink
with Giemsa's stain. The nucleus, circular in shape, lies almost at the centre of the body
of the parasite, it stains light pink and is surrounded by a well-marked membrane. It contains
a number of darkly stained chromatic rods which are usually arranged radially along its
margin. The blepharoplast is rod-shaped and measures from 1 . 5 μ in length; it is always
situated about 4μ from the anterior end of the parasite. The flagellum, about 40 μ in length,
consists of a single stout filament which arises from an achromatic space just anterior
to the blepharoplast and passes straight out at the anterior end of the parasite. No undulating
membrane or basal granule can be demonstrated.