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trichomonad type. The dimensions are 7 - o x 4 - 5/a, and 5‘5 x 5/4. There 
is a well-marked cyst-wall. Furthermore, they occur singly, and never 
in groups such as one would look for in the case of a yeast. In Fig. 12 
a single individual appears to be encysted, nucleus, basal granule, and 
axostyle being all recognizable. Fig. 13 shows two rather large deeply- 
staining masses of chromatin at opposite poles of the ovoid cyst; 
between them stretches a dark strand or rod. In Fig. 14 the joining rod 
is disappearing, and the chromatin masses lie at opposite sides of the 
cell. In Fig. 15 it can be seen that the cytoplasm shows the beginning 
of a median constriction. The nuclei are in this case each surmounted 
by a deeply staining granule. Other granules occur scattered in the 
dense cytoplasm, but have not the definiteness of these, which I 
regard as the basal granules. The encysted material was so meagre 
that I am not able to say what stages these several cysts represent. 
Possibly the organism multiplies by simple fission within the cyst; or 
these may be stages in a sexual process, but whether isogamic or 
autogamic, I cannot say. Prowazek described autogamy in T. lacertae. 
Dobell has thrown some doubt on Prowazek’s account, but whether 
Prowazek were right or wrong in the interpretation of what he saw, the 
possibility of sexual cysts occurring in Trichoviastix is by no means 
excluded by Dobell’s description of agamic cysts in T. batrachorum. 
(b ) Spiroehaete. 
In seven larvae 1 a typical slender spiroehaete was found in the same 
region of the gut as the flagellates— i.e. just below the Malpighian 
tubules. The infection was never very rich, but occasionally patches of 
the large epithelial cells of the gut-wall would appear to be covered with 
close-set vibratile cilia—the effect produced by a mass of spirochaetes, 
each attached to the gut-wall by one end, while the free portion 
vibrated ceaselessly. In teased-out preparations of the gut-contents the 
spirochaetes were sometimes found singly, but more often in tufts 
vibrating about a small mass of detritus or bacteria. The usual 
movements characteristic of spirochaetes in general were observed: i.e. 
rapid screwing round the long axis and flexion of the whole body, 
especially at a middle point. 
The movements are exceedingly rapid and hard to follow at first, 
becoming slower after a short time and gradually ceasing; in this stage 
1 In one pupa a very few spirochaetes were seen. The adult caddis-flies examined never 
showed any infection. 
