TRYPANOSOMES IN TSETSE-FLIES AND OTHER DIPTERA, 199 
a form with » terminal, like an ordinary blood-trypanosome, 
is still more in favour of this belief. J would add, further, 
that from the conditions under which T. grayi was found to 
occur in one of my flies (Oct. 10th, p. 232), I am of opinion 
that the host of T. grayi is a bird, probably some of the 
numerous species of diving birds which swarm on the shore 
of the Victoria Nyanza. 
We have next to consider the slender forms, formerly 
regarded by me as male. I do not think this interpretation 
can be maintained, in view of their distribution and mode of 
occurrence in the fly. Thus, in one of my flies (Nov. 10th, 
[1], p. 241), only slender forms, round forms, and H-forms 
occur, and are confined to the proctodeeum (figs. 132-137). 
Some of them are fairly stout and approach young or ordinary 
forms in character, but with » constantly anterior to N. In 
Nov. 10th (2) also we find most. typical slender forms in the 
proctodzeum, but none in the intestine, where ordinary forms 
of all kinds occur (p. 242, figs. 138-150). In Nov. 13th we 
find no slender forms in the stomach, but in the intestine and 
proctodzeum we find both slender forms and typical H-forms 
mixed with ordinary forms (figs. 156-170, p. 243). In Nov. 
14th we find slender forms very sparingly in the stomach and 
intestine, while the proctodzum contains swarms of H-forms 
_and cysts (figs. 171-216, p. 245), Finally, in Oct. 10th we 
find slender forms present fairly commonly in the stomach 
and intestine, together with ordinary forms, but in the procto- 
deeum we find immense numbers of the slender and H-forms, 
without any ordinary forms (figs. 218-233, p. 233). 
The data given above show that the primary habitat of the 
‘slender type is the proctodeeum, of which it may constitute 
the sole trypanosome-fauna ; and further that all other forms 
may be absent altogether from the fly. This, I think, suffi- 
ciently disposes of the notion that the slender form represents 
the male type. From the proctodeum both the slender form 
and the H-form may extend forwards ; it is noteworthy, how- 
ever, that the slender form gets further forward, being found 
in the stomach, while the H-form does not, so far as my 
