180 E. A. MINCHIN. 
size, but are usually absent altogether. In no case have I found 
any signs of T’. gambiense in the tsetse-fly later than 
the fourth day after infection. Nabarro and Greig (81) 
found T. gambiense in G. palpalis up to seventy-one 
hours after feeding; animal trypanosomes up to 100 hours. 
Throughout these four days of development T. gambiense 
undergoes a steady and well-marked increase of size. 
In the other Diptera I found that T. gambiense went 
through the same changes of form and structure as in 
Glossina palpalis. In Stomoxys, however, no trypano- 
somes were found on the second day (forty-eight hours) after 
infection. My mosquito experiments are very incomplete, but 
I found active trypanosomes in Teeniorhynchus as late as 
seventy-two hours after infection. 
In spite of much searching T’. gambiense was never found 
in any organs except those in which digestion of the blood 
was proceeding; that is to say in the stomach and intestine. 
I will now proceed to a more detailed description of my 
observations. 
Preparations made from fliesshortly after infection (July 31st, 
p. 228, and Sept. 8th, p. 229) show the gradual disappearance 
of the trypanosomes of intermediate type by their conversion 
partly into slender forms, but chiefly into stout forms, I think 
it is safe to assume that the intermediate forms with long 
flagellum become converted into slender forms (compare figs. 
41-44), while those with short flagellum become stout forms. 
There are also many dividing forms found at this period, 
indicating active multiplication. The process of differentiation 
is complete twelve hours after infection, and then we have the 
two sharply marked types, slender and stout, which charac- 
terise the first day after infection. Seen in the living condition 
the slender, twenty-four-hour forms appear transparent, of 
serpentine appearance, and very active; the stout forms are 
fish-like or whale-like in form, opaque and Brena and 
sluggish in movement (figs. 102, 103). 
The slender forms (figs. 45, 48, 52, 56-58, 61, 62, -and 
P.R.S., B78, Pl. XI, figs. 1-6) are distinguished in prepa- 
