356 
Protozoa of Lizards, etc. 
end of the body and there is a long undulating membrane along which the 
flagellum runs, to become free at the anterior extremity of the flagellate. In 
the insect’s intestine these forms show not only the trypanosome type but 
also intermediate ones—crithidia and leptomonas—and finally the leishmania 
forms. In flagellates of this group there is again only a single invertebrate 
host and the infection is spread from insect to insect by the leishmania forms 
as m L/eptomonas and Crithidia. A flagellate of this group is Herpetomonas 
muscae domesticae of the common house-fly and it is convenient to distinguish 
these forms by the generic name Herpetomonas. 
In a fifth group there are the same forms as in the preceding group, but 
in place of the single invertebrate host there is a vertebrate one as well. This 
is the group of true trypanosomes which have the generic name Trypanosoma. 
This scheme of classification may have many points against it, but at any 
rate it is convenient and is as far as we can go in our present state of know¬ 
ledge. To subdivide these groups into different genera simply leads to further 
confusion. All we can do is to wait for further data, and such an attempt as 
that made by the late Dr Albert Chalmers (1918) to split up the genus Try¬ 
panosoma into his extraordinary series of new genera only tends to bring con¬ 
fusion into an already difficult subject. 
The scheme I have outlined above has the merit of simplicity and it can 
be arranged in tabular form in the following manner. The names in the right- 
hand column (Text-fig. 1) are merely descriptive and should be used in an 
adjectival sense. They may be employed for any particular stage which may 
appear in the development. Those in the left-hand column are generic titles 
and, as such, should be written in italics and with a capital. We can speak, 
for instance, of the leptomonas stage of Leishmania tropica , the crithidia stage 
of Trypanosoma lewisi , or the leishmania stage of Herpetomonas muscae 
domesticae. 
There is one group of flagellates which do not enter into the above scheme. 
I refer to the curious leptomonas form first described by Lafont from the latex 
uf Euphorbias as Leptomonas davidi. The work of Lafont, Bouet and Roubaud, 
and more recently of Fran§a (1919), has demonstrated that this flagellate 
undergoes a cycle in a hemipteron and is transmitted by it to healthy plants. 
Thus we have a flagellate of the leptomonas type which has both an insect 
and a plant host. Evidently it cannot be included in any of the genera defined 
above. For these flagellates we may employ the name Phytomonas, first sug¬ 
gested by Donovan (Lancet, 1909), the type species being Phytomonas davidi 
(Lafont, 1909). 
If the flagellates of this most confusing group were named according to 
the scheme outlined above we should at any rate understand from their names 
something of their life history and structure. 
The question now arises into what group we are to place the flagellates of 
the gecko, the anolis and the chamaeleon. I think we are safe in assuming 
that there must be invertebrate hosts. The two former would undoubtedly 
