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Philippine Journal of Science 
1019 
their life cycle. As the snails are kept longer in the aquarium 
the balantidia apparently increase in numbers in the water of 
the aquarium. Whether or not they divide under these cir- 
cumstances cannot be said. Outside of the snail, however, they 
seem to have but a short period of existence, as free-living 
forms, since they disappear in four or five days. Whether they 
encyst at this period or succumb to the toxic substances pro- 
duced by the overgrowth of bacteria and spirilla is yet to be 
determined. So far, the cysts have not been determined with 
certainty. 
SITE OF PARASITISM 
Smear preparations of entire organisms and sections 5 n 
thick cut from different portions of the gut show that the 
parts most infested are the mid- and the hiiid-guts, especially 
those parts usually rich in intestinal contents from which the 
animal mainly derives its food. 
In these sections the organisms were always found confined 
to the lumen of the gut, lying in the intestinal content. I never 
have observed an instance where tissue had been invaded or, 
indeed, any evidence that might be interpreted as an attempt 
to penetrate the intestinal wall. 
MORPHOLOGY 
In fresh preparations the organism has the appearance of 
a miniature balloon, slightly flattened dorsoventrally, tapering 
evenly and gradually to a blunt anterior end and expanding into 
a posterior rounded extremity where, often, a very minute con- 
ical papilla can be seen. At this spot is located a minute anal 
opening, the cytopyge, attached to which, in an actively feeding 
animal, can be observed a stalk that looks like a mucoid thread. 
In one instance I observed an individual attached to a fragment 
of intestinal tissue by means of this “stalk.” The structure, 
in a way, recalls the attaching organ of the free-living hypo- 
trichous ciliate Ancystropodium maupasi as described by Faure- 
Fremiet. (4) The anal papilla somewhat resembles apparently 
similar structures figured by Stein in connection with his descrip- 
tions of Balantidium coli and B. duodeni. 
Viewed from the sides the dorsoventral flattening of the body 
is very apparent. Ventrally, at about the junction of the ante- 
rior and middle thirds of the body and just at the site of the 
ventral lip, the median portion is depressed, forming an in- 
pocketing that constitutes the triangular excavation at the bot- 
tom of which lies the opening of the cytostome. Under normal 
