GENUS BA LANTIDIUM. 577 



GENUS II. BALANTIDIUM, C & L. 



Animalcules free-swimming, ovate or fusiform, subcylindrical, slightly 

 truncate in front; peristome-field but little excavate, straight, somewhat 

 triangular, widest anteriorly, terminating posteriorly towards the centre 

 of the ventral surface in a narrow cleft, the left border only bearing the 

 large adoral cilia ; pharynx absent or rudimentary ; anal aperture postero- 

 terminal ; endoplast ovate or linear ; contractile vesicles usually numerous. 

 Occurring mostly as parasites within the intestinal viscera of vertebrate 

 animals. 



The Bursaria entozoon of Ehrenberg is made the type of this genus by Claparede 

 and Lachmann, to which Stein has added three new forms. These are to be 

 distinguished from Bursaria proper by the more simple and non-excavate character 

 of the peristomal area, and by the absence of the extensively developed pharynx, 

 which constitutes so essential a characteristic of the single representative of the last- 

 named genus. 



Balantidium entozoon, Ehr. sp. PL. XXIX. FIG. 3. 



Body ovate or pyriform, narrowest anteriorly, from one and a half to 

 twice as long as broad, the narrower anterior end somewhat curved to one 

 side, obliquely truncate ; peristome-field extending backwards to the 

 centre of the ventral surface, almost median, but inclining obliquely slightly 

 towards the right, of considerable width in front, forming a short narrow 

 throat posteriorly ; contractile vesicles usually four in number, two situated 

 on either side, often rosette-shaped ; endoplast sausage-shaped, curved, with 

 a distinct, subcentrally attached endoplastule. Length 1-240" to 1-40". 



HAD. Parasitic within the rectum of the common and edible frogs, 

 Rana temporaria et esculenta. 



This species typifies one of the earliest known infusorial forms, it corresponding 

 in part with the "Animalcula in stercore Ranarum" described and figured by 

 Leeuwenhoek in the year 1722. In addition to its identity with the Bursaria 

 entozoon of Ehrenberg, it is now recognized as synonymous also with the Bursaria 

 nudetts of that authority, with the Paramecium nucleus of Schrank, and with the 

 Leucophrys entozoon of Stein. Experiments made by the last-named investigator 

 elicited the fact that this animalcule cannot survive more than a day or two's 

 isolation in ordinary fresh water, unless this medium is mingled with the co'ntents 

 of the frog's intestine, thus proving the creature's essentially parasitic nature. 



Balantidium elongatum, Stein. 



Body elongate-fusiform, subcylindrical, from two to two and a half 

 times as long as broad, the anterior end pointed or slightly obliquely 

 truncate ; peristome-field median, narrow, cleft-like, not extending back- 

 wards beyond a quarter of the length of the entire body ; no distinct 

 pharynx ; contractile vesicles two in number, situated medially towards 

 the posterior extremity of the ventral surface; endoplast ovate. 

 Length 1-120" to 1-84". 



HAB. The intestinal canal of Triton taniatus and Rana esculenta. 



VOL. II. I 



