W. S. Patton and C. Strickland 
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outlined by Roubaud in our opinion may quite well represent the 
development of two distinct flagellates of G. palpalis ; one of these may 
be grayi, which we know encysts in this fly, while the other may be 
that known as tullochi, and it is possible the latter is transmitted 
hereditarily. Minchin’s work on the encystment of grayi has not been 
followed up, on the contrary we find this flagellate is still regarded as a 
vertebrate trypanosome, and nothing whatever is known of the species 
tullochi. 
Before concluding these remarks on the flagellates of tse-tse flies, 
we would like to urge on workers who have the opportunity of studying 
these parasites that it is of the utmost importance to ascertain how 
they are transmitted from one fly to another. We know the species 
grayi encysts in the rectum of G. palpalis ; these cysts and their 
further development should next be looked for in the stomachs of this 
fly, either before it has first fed or soon after. The infection probably 
takes place in nature by the flies ingesting the cysts accidentally either 
before they fly off to get their first feed of blood or when they return 
to their breeding grounds between their several feeds. One experiment 
of Minchin’s, quoted above, shows that it is possible to infect a clean fly 
in captivity. Freshly hatched out G. palpalis (after first ascertaining 
that they have not got a flagellate which is transmitted hereditarily), 
should be put in cages in which wild flies G. palpalis have been kept, 
some of these are sure to pass out the cysts of T. grayi in their 
faeces and it could then be seen whether the clean flies become 
infected. 
In the case of G. fusca, and this applies also to all the other tse-tse 
flies, it could be readily demonstrated whether its flagellate is 
transmitted hereditarily by raising flies from infected parents and then 
feeding them on clean animals ; pupae raised from infected flies should 
certainly be examined. It is important to keep in mind the possibility 
of any species of tse-tse fly being infected with two distinct flagellates, 
one of which may encyst in the rectum of its host and the other be 
transmitted hereditarily. One of us (1908) has recently made a 
suggestion which we have found of great use in studying these natural 
flagellates, and that is to divide their life-cycles into three stages, 
pre-flagellate, flagellate and post-flagellate ; although these stages are 
not sharply separated from each other they are sufficiently distinct to 
enable anyone to follow the various forms as they occur in the flies. 
We believe that until these flagellates are completely studied, apart 
from any possible developmental form of trypanosomes, the important 
