104 
Haemoflagellates, etc. 
represents that in which T. grayi occurs in its vertebrate host (avian). 
(2) This type is constituted by slender, elongated parasites with well- 
developed undulating membrane and flagellum ; it occurs chiefly in the 
hind gut of the fly. (3) Very narrow thin forms of a typical Herpeto- 
monad structure with practically no undulating membrane. The 
parasites were found in the proctodaeum and produced the cysts of 
T. grayi. 
In criticising the above work we would like to first point out that we 
do not agree with Minchin that this flagellate of G. palpalis has any¬ 
thing to do with a vertebrate trypanosome, but that it is a natural 
Crithidia of the fly. Minchin’s hypothesis as to its origin is based solely 
on the habits of the tsetse fly; beyond certain observations on the 
feeding habits nothing is known of the behaviour of tsetse flies at their 
breeding grounds. In his recent paper Minchin (1908) dismisses Novy’s 
original suggestion, that T. grayi is a fly parasite, by saying: “ At the 
present time true trypanosomes are only known to occur in the blood of 
vertebrates, and in the stomachs of insects which suck the blood of 
vertebi'ates; hence, it is reasonable to assume that the insects in ques¬ 
tion obtain their trypanosomes from the vertebrates. When trypano¬ 
somes have been found in plant juices or stagnant waters it will be 
time enough to speculate on the possibility of blood-sucking insects 
obtaining them from such sources.” Has Minchin studied this parasite, 
or any similar flagellate which encysts in the rectum of a blood-sucking 
insect, sufficiently to justify this statement ? Did he, while in Uganda, 
endeavour to find the cysts of T. grayi in the faeces of G. palpalis in 
his fly cages, on twigs or even in plant juices or other places where 
the flies might deposit their excreta ? We can find no reference to 
this in his paper. We would like to point out to him that we do not 
expect to find trypanosomes in plant juices or stagnant waters, but the 
cysts of a Crithidia, which is a very different thing. We have shown 
that these flagellate cysts are well adapted for an extracorporeal 
existence and that they can resist desiccation. We will here refer to one 
parasite which we have studied and which fully bears out our view. 
While making a study of II. culicis in C. pipiens and C. fatigans we found 
the encysted stages of the flagellate in the rectum of the mosquito as 
well as in its excreta. Exactly similar bodies were recovered from the 
alimentary tracts of the larvae of the insects. A study of the habits of 
the mosquito clearly explained the method of infection. The mosquitoes 
in one particular tank collected in large numbers in a dark corner just 
above the water were they subsequently laid their eggs. They were to 
