196 EK. A. MINCHIN. 
The first sign of encystment isa shortening of the flagellum, 
which at the same time appears to become thicker and more 
distinct, an effect perhaps largely due, however, to its being 
difficult to distinguish the exact limits of the flagellum from 
the slender anterior prolongation of the body (compare figs. 
189, 192). While the flagellum is becoming retracted the 
cyst-wall begins to appear round the hinder end of the body 
(figs. 189-193) in the form of a granular secretion, which 
stains a dull red with Giemsa’s stain. The rate at which the 
cyst is formed shows great variations relatively to the retracta- 
tion of the flagellum. In some, with the flagellum still long, 
an abundance of the cyst secretion is seen (fig. 190). In 
others, with the flagellum almost completely retracted, the 
cyst is only just beginning to be formed (fig. 193). The 
substance of the cyst-wall appears to be made up of distinct 
masses or grains of the red-staining substance, between which 
is a more fluid matrix, and appearances are often obtained 
very similar to those figured by Prowazek for Herpetomonas 
musce-domestice (85a). The term ‘ Schleim-cysten,”’ 
applied by Prowazek to the cysts of Herpetomonas, appears 
suitable for the present case also, as the frequency with which 
burst or damaged cysts are met with (figs. 192, 195, etc.) 
indicates that the substance of the cyst-envelope is of a soft 
nature. . 
While the cyst-wall is being secreted the retractation of 
the flagellum is proceeding, until all that can be seen of it is 
a round or oval red-staining mass, connected by a red streak 
with the blepharoplast (figs. 194, 195). The appearances 
seen at this stage (which is of very common occurrence) are 
remarkable, and suggest strongly the “flagellar vacuole ” 
described by Leishman as giving rise to the flagellum in the 
flagellated culture-form of Leishmania. Here, however, 
the flagellar vacuole, if it may be so termed, is, in its relation 
to the flagellum, the inverse of that of Leishmania—that is 
to say, it does not precede its formation but results from its 
retractation. The flagellar vacuole disappears and only the 
streak is left (fig. 196) ; finally the streak fades away too, and 
