0. M. Wenyon 
observers (1914) have suggested that the flagellate of the gecko may in reality 
be Leishmania tropica, and that it is transmitted to man by the Phlebolomns 
which feeds on the lizards. On account of their importance it would be well 
if the inoculation experiments were repeated by other observers. 
In the present state of our knowledge it is difficult to name many of these 
flagellates. Some time ago (1913) I outlined a scheme for the classification of 
these flagellates in the following manner. There is a group, confined entirely 
to the insect or invertebrate host, which in its most highly developed stage 
has the leptomonas structure. Small round leishmaniform bodies, protected 
by what must be a cyst wall, are developed from the leptomonas forms and 
escape in the insect’s faeces. They are ingested either by the larvae or adults 
of the insect and lead to their infection. There is thus only a single invertebrate 
host and such forms can be distinguished, at any rate at present, by the 
generic name Leptomonas. This name was first employed by Kent (1881) for 
a flagellate seen by Biitschli in 1878 in a nematode worm Trilobus gracilis. 
Kent named it Leptomonas butschlii, but whether it is a leptomonas as we now 
understand it cannot be determined till this organism is re-examined in the 
light of present knowledge. Meanwhile we shall employ the name Ijeptomonas 
as above defined. 
Another group of flagellates, in which the highest stage of development is 
again the leptomonas form, includes the parasites of leishmaniasis. Here, 
however, there is a vertebrate host in which the leishmaniform parasite is 
most usually seen, but also occasionally the leptomonas, as I have shown 
(1915). The latter is generally encountered only in cultures in the test-tube 
or in certain invertebrates which have ingested the leishmania forms along 
with a quantity of blood. There is undoubtedly an invertebrate host of this 
flagellate and in it the infection would be expected to resemble a true lepto¬ 
monas of an invertebrate. In order to distinguish these flagellates which have 
a vertebrate as well as an invertebrate host from the purely insect form—the 
true Leptomonas —the generic name Leishmania can be employed. 
A third group of flagellates attains a still higher stage of development 
and the individual flagellate is known as a crithidia. In it the kinetoplast is 
close to, but still in front of, the nucleus, and there is a short undulating 
membrane running from just in front of the kinetoplast to the anterior end 
of the flagellate. Along the edge of this runs the flagellum, to become free at 
the anterior extremity of the flagellate. The crithidia live in the intestine of 
invertebrates and in the posterior part of the intestine there are produced 
small leishmania forms, as in the leptomonas, and they are responsible for the 
spread of infection from host to host. There is again only a single host—an 
invertebrate—and such forms may be considered under the generic name 
Crithidia. We know of no flagellate of this type which has both a vertebrate 
and an invertebrate host corresponding to the Leishmania. 
A fourth group shows a still higher development in that the true trypano¬ 
some structure is attained. The kinetoplast is further back at the posterior 
