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 m 

 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-hmma- 

 tein method of Dobell.(2) Total mounts were stained with 

 Delafield's hematoxylin 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 snail? 

 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 



'Saturated solution of mercuric chloride in sea water, 95 parts; glacial 

 acetic acid, o parts. 



' Saturated solution of mercuric chloride in 10 per cent formol, 9 parts; 

 glacial acetic acid, 1 part. 



