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A Critical Revieiv, etc. 
observers stated they had discovered the development of T. gambiense 
and T. brucei in the Glossinae, but the later work of Novy (1906), 
Minchin, Gray and Tulloch (1906) has shown that tse-tse flies harbour 
natural flagellates in their alimentary tracts, and that these parasites 
are not connected with the pathogenic trypanosomes, T. gambiense and 
T. brucei. Minchin (1908), in his recent studies of these flagellates, 
made the important discovery that one of them, T.grayi, encysts in the 
rectum of G. palpalis; although at first agreeing with Novy that it is 
not connected with a vertebrate trypanosome, Minchin now regards it as 
an avian trypanosome. Minchin however does not attempt to explain how 
the cysts of T. grayi find their way back to the fly; it is presumed they 
are ingested by some bird, pass into its blood, and are again taken up 
by the fly when feeding on the bird. This extraordinary hypothesis 
appears to be based solely on the habits of the tse-tse fly as it is known 
to feed exclusively on the blood of vertebrates. In our opinion this fact 
does not exclude the possibility of these flies accidentally ingesting the 
cysts passed out in the faeces of other flies. At present very little is 
known of the habits of the Glossinae , and in order to understand how they 
may ingest these cysts it is important to find out whether they congre¬ 
gate at their breeding grounds, what they do shortly after hatching out, 
whether they fly off immediately to get a feed of blood or whether they 
remain sometime at their breeding grounds. These are certainly the 
occasions when they may accidentally ingest cysts passed out by other 
flies on leaves, twigs, etc. It is well known that blood-sucking species of 
Tabanids insert their proboscides into dew and other fluids on leaves, 
etc. when running about on these objects at their breeding grounds. 
It is important to examine tse-tse flies before they have had their first 
feed or even immediately after to see whether they contain any stages 
of T. grayi or other flagellates. In any case, we believe the cysts of 
T. grayi and their development into flagellates should be searched for 
in the alimentary tract of G. palpalis. The fact that Minchin (1908) 
and Stuhlmann (1907) found bacteria in the stomachs of tse-tse flies 
further confirms our view that these flies may become infected with 
other organisms, and we can find no proof either in Minch in’s paper or 
in Stuhlmann’s that these bacteria are derived from the blood these 
flies ingest or are inherited by them. 
The single instance of a fly bred in captivity becoming infected with 
T. grayi after feeding on a fowl Minchin would regard as proof positive 
(sic) that this flagellate is an avian parasite. We can, however, find 
no mention of the fowl having trypanosomes in its blood, and Minchin 
