TRYPANOSOMES IN 'TSETSH-FLIES AND OTHER DIPTERA. 195 
granulations, which frequently occur in front of the kineto- 
nucleus. The undulating membrane is sometimes distinct 
(fig. 163), but as arule isrudimentary or absent. The flagellum 
is very long and very slender and delicate; it stains feebly or 
not at all, and is often difficult to trace. A typical example of 
this type ‘is unmistakable, and contrasts sharply in many 
points with the slender type described above. 
The H-forms have been found by me becoming encysted 
in great numbers in the proctodeum of one of my flies 
(Nov. 14th, p. 246). I have two smears of this specimen; one 
of them is a thin smear, the other much thicker. Both the 
smears show all stages of the encystment in abundance, but 
in the thin smear the cyst-wall, when developed, is nearly 
always more or less damaged, being evidently of soft con- 
sistence. In the thick smear the cyst-wall is usually intact 
and perfect, but the finer details of the contained body are 
not so well shown. Figs. 186-197, 202, 203 are drawn from 
the thin smear, as were also the figures published by me in 
my preliminary communication to the Royal Society (P.R.8., 
B79, p. 37). . Figs. 198-201 are from the thicker smear, 
which I had not examined at the time of making my pre- 
liminary communication. 
My preparations of the proctodzeum show, in the first place, 
a certain number of young forms of the ordinary type (figs. 
183, 186). Similar young forms are also found as the pre- 
ponderating type of trypanosome in the hinder part of the 
intestine of the same fly (p. 245), a fact of interest as indicat- 
ing that the H-type arises from the young forms of the 
ordinary type. In the second place the smears show a large 
-number of the H-forms (figs. 187, 188), which are also found 
sparingly in the hinder part of the intestine. In life they 
were observed swimming freely, and also occurring in masses 
attached to the wall of the proctodeum. In the third place 
there are the various stages of encystment, from the earliest 
modification of the H-form to the ripe cyst in its final form 
(figs. 189-202). The cysts atall stages were free in the lumen 
of the proctodzum, and not attached in any way to its walls. 
