12
It will be remembered Leger in his description of Crithidia fasciculata based the generic
name on the short oat-like appearance of the parasite of Anopheles maculipennis. This stage as
I have pointed out in my paper on Crithidia gerridis is undoubtedly a young form of the parasite
and as the immature forms of many Herpetomonas have very much the same appearance it is not
possible to distinguish beween the two especially when they both occur in the same insect. The
adult flagellate of Crithidia is very characteristic, the anterior end instead of being blunt as in
Herpetomonas is attenuated being drawn out along the flagellum to which it is attached by a
narrow undulating membrane. Further the blepharoplast is always situated. much closer up to
the nucleus than in the adult flagellate of Herpetomonas. Throughout their life-cycles these
Crithidia have their blepharoplasts either at the anterior end. or close up to the nucleus and
in some instances posterior to it. The generic name Crithidia is therefore an unfortunate one
as it does not accurately describe the peculiar structure of the parasites.
Recently Novy has studied the flagellates found by Koch, Gray and Tulloch in Glossina
palpalis in Uganda ; he believes these flagellates are true insect parasites and have no connection
with Trypanosoma gambiense ; he bases this view on the following facts :
—
(1)The flagellates have been found. in flies which had not fed. on infected animals,
(2) the failure to obtain any development of the trypanosomes ingested by flies fed on
infected animals as well as the many failures to infect susceptible animals with these flagellates,
(3)their analogy with the flagellates of mosquitoes. To this may be added Minchin's
observations on the encysted stages of one of these flagellates T. grayi in the rectum of Glossina
palpalis.
A study of the figures of T. grayi given by Novy, Minchin, and Gray clearly suggest that
this flagellate is more closely related to Crithidia than to the true trypanosomes of vertebrates ;
a comparison of these figures with those of Crithidia gerridis further supports this view.
Trypanosoma grayi exhibits the same pleomorphisism in its adult stage,—long thin forms with
free flagella measuring up to 48 µ as well as short stouter forms being seen. From our present
knowledge of this parasite it is impossible to place it finally either among the Crithidia or the
Trypanosomes and it is quite possible the other flagellate named by Minchin Trypanosoma
tullochi is but a stage of T. grayi. Until the complete life cycles of these parasites are worked
out these points must remain sub-judice.
A similar trypanosome-like flagellate Trypanosoma Christophersi (Novy) has been found
in the dog tick Rhipicephalus sanguinens in Madras by Captain Christophers, I.M.S., it is not
Possible to say whether it is a natural parasite or the development of a vertebrate form.
In summing up our present knowledge of these flagellates the following should. be noted :
—
A large number of insects, blood sucking and non-blood-sucking, have natural flagellates
in their alimentary tracts and are in no way connected. with vertebrate Hœmoflagellates. The
methods by which these insects acquire the infection varies according to the particular insect.
In mosquitoes the larvæ ingest the cysts so that when they hatch out into adults they .have
the flagellates in their alimentary tracts ; in the case of fleas I have found that the larvæ also
ingest the cysts and that here the early stages of the parasite should. be . looked for in the
alimentary tracts of the larvæ, In non-blood-sucking flies such as Musca domestica, Lucelia,
Sarcophaga, the cysts are ingested by the adult insects. In blood-sucking flies such as
Stomoxys and Tsetse flies as well as in ticks the method of infection is not clear. A species of
Stomoxys observed here after sucking blood. has the habit of sitting on shrubs close to its host
where it deposits its fæces ; the question which naturally suggests itself is whether the flies at
any time suck up any of the fasces and thus become infected ? I am however inclined to
think the larvæ ingest the cysts. This point is of some importance as in the case of tsetse flies
which only suck blood., Minchin suggests the encysted stages of T. grayi are probably ingested
by some vertebrate ; this can however hardly be the case. The larvæ of these flies should be
examined for the early stages of these flagellates. In the case of ticks it would seem neces-
sary for the parasites to pass to the ova and thus be transmitted hereditarily, because ticks
only feed on blood in all their stages and. further there is no means as far as I am aware for
the encysted stages to pass out of the ticks. I have been able to confirm this theory in the
case of a flagellate I recently found. in a species of Hœmyphysalis probably H. Neumanni, Dönitz1
very common on Lepus nigricollis. The flagellates pass to the ovaries and can be followed
through the ova to the young larvæ where they rapidly develop into flagellates 12 hours after
dopping from their host. This interesting parasite will be described in detail later. Bugs
whether terrestial or aquatic become infected either by the nymphs or adults ingesting the
encysted stages.
The study of these natural flagellates is of great importance as they are veritable obstacles
in the investigation of the developement of
Hœmoflagellate in blood-sucking insects, and as I
have shown above they will undoubtedly throw further light on the parasites of Kala-Azar
and Delhi Boil.
1 Professor H. B. Ward informs me that Mr. Swingle, a pupil of his, has also found a flagellate in the American
sheep tick, (Melophagus ovinus), which is transmitted hereditarily ; Pfeiffer has described a Crithidia from this insect.