xv, 4 De Leon: Balantidium Haughwouti 393 
they have given new specific names. In the latter case the ques- 
tion arises as to the validity of these species, and further work 
on them is clearly indicated. 
MATERIAL AND METHODS 
In studying the parasite to be described the snail host was 
dissected, the intestinal tract isolated and where whole mounts 
were needed the intestinal contents were teased out, smeared 
directly over the slides, and immediately fixed. Intestines were 
sectioned at different levels to detect the site of parasitism as 
well as to throw light on the matter of tissue invasion. Sec- 
tions of individual balantidia were also prepared for the study 
of the minute cytoplasmic and nuclear structures. In every 
case fixation was carried out either in sublimate-acetic fluid 2 or 
in Bouin’s picro-aceto-formol solution. Sections were stained 
either by Heidenhain’s iron-hsematoxylin or by the iron-haema- 
tein method of Dobell. (2) Total mounts were stained with 
Delafield’s htematoxylin or with the picro-carmine of Hoyer. 
The living organisms were studied in the intestinal fluid of 
the host or in physiological salt solution. 
The animals to be measured were killed in Worcester’s fluid 3 
and measured directly by the ocular micrometer at a magnifica- 
tion of 1,280 diameters. Both large and small individuals were 
taken at random as they occurred on the slide. 
The proportion of infected snails was found to be about 95 
per cent, after the animals had been kept in the laboratory 
aquarium for a few days ; but if examined immediately after they 
were taken from the pond, fully 99 per cent of well-fed snails 
containing an abundance of food in the gut were found to be 
parasitized. As the snails are kept longer in the laboratory 
and the intestinal contents diminish as a result of the lessening- 
food supply the heaviness of the infection is correspondingly 
lowered. Under such conditions of partial starvation the para- 
sites look lean, flat, transparent, and granular, instead of robust 
and alveolar. If they are kept a few weeks longer in the labor- 
atory, examination of all the snails will prove negative. 
Under these conditions the parasites apparently leave their 
host, either being discharged with the intestinal contents or 
swimming out by themselves to assume the exogenous phase in 
2 Saturated solution of mercuric chloride in sea water, 95 parts; glacial 
acetic acid, 5 parts. 
3 Saturated solution of mercuric chloride in 10 per cent formol, 9 parts; 
glacial acetic acid, 1 part. 
