W. S. Patton 
103 
sites spread forward to the proventriculus where they became long forms, 
which Woodcock regards as corresponding with the slender forms of the 
flagellate of Pontobdella muricata. 
In the proboscis of freshly caught tsetse flies Stuhlmann found little 
crithidial forms, which he regards as the stages of the parasite which are 
destined to pass back to the vertebrate. He however was unable to in¬ 
fect any vertebrate with T. brucei by injecting these parasites into them. 
Woodcock in trying to explain this discrepancy says, “There is some 
other, as yet unknown, factor or condition concerned in this perplexing 
question.” We consider the perplexity arises from the fact that Stuhl¬ 
mann failed to recognise the possibility, in fact certainty, of G. fusca 
being infected with a natural flagellate. Stuhlmann bred G. fusca from 
pupae and concluded the flies were free from infection, in other 
words, that hereditary transmission of the flagellates of tsetse flies does 
not take place. We can find nothing in Stuhlmann’s paper proving this 
to be the case. Why did he not examine the alimentary tracts of 
the pupae for flagellates or their earlier stages ? This should certainly 
have been done. Further, careful control experiments by feeding flies 
on clean animals should have been carried out and they should then 
have been examined for flagellates, but this appears to have been over¬ 
looked. All subsequent observers have accepted Stuhlmann’s observa¬ 
tions and have not attempted to exclude a natural flagellate of G. fusca. 
It is quite obvious Keysselitz and Mayer (1908) have fallen into this 
trap. 
It will be remembered that Stuhlmann fed his raised G. fusca on 
animals infected with T. brucei and from two to four days later found 
that 80—90°/o of the flies were swarming with flagellates. He then 
describes these flagellates as representing the cycle of development of 
T. brucei. A careful reference to his description and figures leaves us to 
imagine how T. brucei comes to develop into the flagellates of the fly. 
The masses of flagellates lining the intestinal epithelium clearly suggest 
a natural parasite, and to anyone who has studied a large number of 
these parasites this is at once evident. We therefore cannot accept this 
work as being accurate, and we regard his developmental forms as a true 
Crithidia of G. fusca which is transmitted hereditarily. 
Minchin (1908), in his work on the development of Crithidia grayi in 
G. palpalis, describes three forms of this flagellate : (1) the ordinary type 
having a multiplicative function and giving rise to the swarms of para¬ 
sites often found. It is usually of large size, and the blepharoplast shows 
great variability in its position ; Minchin thinks this form most nearly 
