388 
two sides of the sac, as seen one through the other, showed 
that the small end of the sac was twisted as well as bent over 
on itself. A pale, clear nucleus and a very few granules 
were also seen. In life the broad membrane undulates 
vigorously in a series of waves, the flagellum taking part, and 
presents then a deeply toothed appearance (fig. 1). _ The 
movements produced by the activity of this membrane tend 
to urge the animal in a wide circle. The opposite extremity 
of the sac twists and untwists itself to a small extent also 
during life. ‘The series of waves of the undulating mem- 
brane are not incessantly in one direction; after a certain 
time they change to the opposite direction, and then resume 
their original direction, an alternation of from right to left 
and from left to right being kept up. When minute traces 
of acetic acid vapour are passed into the gas chamber, where 
this infusorian is, it soon becomes affected. The undulations 
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w ( 
\ 
i 
\ 
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\ Wi" 
\ 
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FIG.S. ae J FIG.2. 
become deranged, starting from both ends simultaneously and 
meeting in the middle, and at length ceasing (fig. 2). 
In the blood of one frog, where these parasites are not 
unfrequent, about five or six in a drop of blood as big as a 
large pin’s head, I noticed very numerous minute oblong 
bodies, which reminded me strongly of the pseudo-naviculee 
which I have found in the cysts of the Gregarina parasitic 
in Tubifex rivulorum. These little oblong bodies (fig. 4) 
were in many cases attached to the end of the red blood-cor- 
puscles (fig. 3), just as I have seen the similarly sharply termi- 
nated pseudonavicule of Tubifex attached to pieces of tissue- 
