404 Philippine Journal of Science mo 



sap. The single granule would appear to be in the nature of 

 an endosome floating free in a sac containing nuclear sap and, 

 possibly, plastin. In well-differentiated specimens there appears 

 to be an inlying achromatinic network upon which, in many 

 cases, are distributed chromatinic granules. These granules do 

 not appear in all nuclei and their presence may betoken im- 

 pending nuclear division. 



The normal position of the micronucleus is at the concavity 

 of the meganucleus where it fits very nicely and where the meg- 

 anucleus eventually encloses it within its folds. At times it 

 can be seen well sunk in the notch, and at other times it is lying 

 only on the edge. It may wander out of the meganuclear notch 

 (see fig. 3, i) and be found anywhere near the meganucleus or 

 completely separated from it and floating alone in the endoplasm. 



Although there is good ground for believing that this animal 

 forms cysts, I have been unable to identify any of them with 

 certainty. Apparently they occur rarely or not at all in the 

 intestinal contents and it seems likely that, after a brief free- 

 swimming stage in the pond water, the ciliates round out and 

 form cysts which settle on aquatic plants to be later taken in 

 by other snails. In other words, apparently the conditions in 

 the intestines of the host as regards food supply are sufficiently 

 favorable to preclude the formation of cysts there in the general 

 run of infections. 



Outside of the snail the animals die quickly under experi- 

 mental conditions. Under natural conditions it is possible that 

 encystation takes place exogenously as has been suggested. 



The question of the exogenous life of Balantidium is of some 

 interest from the viewpoint of preventive medicine. As regards 

 Balantidium coli several observers have reported it as occurring 

 free. Kleine(7) states that he never failed to find "Paramecium 

 coli" or Trichomonas in the sewage as it passed out of St. Bar- 

 tholomew's Hospital, London. He adds that if he wanted to 

 obtain numerous specimens of these organisms all that was nec- 

 essary was to bottle specimens of the highly diluted sewage and 

 keep them for a period of about three weeks, after which abun- 

 dant organisms were available. 



Such an observation as this requires careful confirmation. In 

 the first place, it practically presupposes an instance of Balantid- 

 ium infections out of all proportion to those that have been 

 reported. It seems highly probable here that Kleine mistook 

 other members of the family Bursarida* for Balantidium. 

 Conn(l) with some reservation has reported Balantidium coli as 



