W. S. Patton 
105 
be found here in the day digesting the blood they had sucked the night 
before and undoubtedly passed their faeces into the water. Without 
actually finding the cysts of H. culicis in the water it was quite evident 
that the larvae ingested them accidentally while feeding on the surface 
of the water. We would draw Minchin’s attention to these observations, 
for we believe, that if a careful study of the habits of the tsetse fly at its 
breeding grounds had been carried out, it would have been found that 
the flies accidentally ingest the cysts passed out in the faeces of other 
flies. A careful search should have been made in the alimentary tracts 
of a large number of specimens of G. palpalis for the cysts and the early 
stages of their development. Flies bred in captivity should have been 
placed in cages with wild flies to see if they became infected. One 
experiment carried out by Minchin suggests that this actually took 
place ; he however interprets it in quite another way because the fly was 
unfortunately fed on a fowl. We are not even told whether this fowl 
had trypanosomes in its blood; this is a strange omission. 
Before concluding that T. grayi undergoes the complicated cycle as 
suggested by Minchin, it would have been wiser to have first excluded a 
simpler and more natural life cycle such as we have suggested. Such 
complicated cycles are not common in nature. We believe that if T. grayi 
had been studied along the lines we have suggested the confusing 
number of forms described and figured by Minchin would have fallen into 
their natural places. We cannot agree with him in his description of the 
Herpetomonad forms. The flagellates he depicts as such are certainly 
not like a Herpetomonas ; their anterior ends are drawn out along the 
flagella, clearly pointing to the presence of a narrow undulating mem¬ 
brane (see figures of G. gerridis ). No Herpetomonas has this appearance. 
T. grayi we would then regard as a natural flagellate of G. palpalis 
belonging to the genus Crithidia ; it is transmitted from one fly to the 
other by means of cysts which are accidentally ingested by other flies. 
The Crithidia of G. fusca on the other hand is transmitted hereditarily, 
and this accounts for the differences in the methods of development of 
the two parasites which have so perplexed Minchin, Stuhlmann and 
others. 
Mode of Transmission of Trypanosomes by Tsetse Flies. 
In an earlier part of this paper we pointed out that the study of the 
life cycles of trypanosomes was intimately connected with the elucidation 
of the methods by which they are transmitted in nature. In the course 
