638 PROTOZOOLOGY 



B. truncatella M. (Fig. 300, a). SOO-lOOOju long. 



Genus Thylacidium Schewiakoff. Similar to Bursaria in general 

 appearance; but smaller in size; peristome simple in structure with- 

 out longitudinal fold; with zoochlorellae; fresh water. One species. 



T. truncatum S. (Fig. 300, b). 60-lOOju long. 



Genus Bursaridium Lauterborn. Similar to Bursaria; peristome 

 funnel turns to right; fresh water. 



B. difficile Kahl (Fig. 300, c). Anterior end truncate, cyto pharynx 

 slanting toward right; about 130/x long. 



Genus Balantidium Claparede and Lachmann (Balantidiopsis 

 Biitschli; Balantiodoides Alexeieff). Oval, ellipsoid to subcylindrical; 

 peristome begins at or near anterior end; cyto pharynx not well de- 

 veloped; longitudinal ciliation uniform; macro nucleus elongated; a 

 micro nucleus; contractile vacuole and cytopyge terminal; in the gut 

 of vertebrates and invertebrates. Numerous species. Hegner (1934) 

 states that the size and shape of body and macronucleus could be 

 made a satisfactory basis for specific identification. 



B. coli (Malmsten) (Fig. 301). Ovoid; 40-80^ by 30-60m, but 

 length varies 30-1 50ai; body covered by many slightly obliquely 

 longitudinal rows of cilia; peristome small near anterior tip, lined 

 with coarser cilia; inconspicuous cytostome and cyto pharynx are 

 located at the end of peristome; 2 contractile vacuoles, one terminal, 

 the other near the middle of body; macronucleus sausage-shape 

 and a vesicular micronucleus; cytopyge near the posterior tip; food 

 particles are of various kinds, including erythrocytes and other host 

 cell fragments, starch grains, faecal debris, etc. The trophozoite 

 multiplies by binary fission. Conjugation was reported by Brumpt. 



The cysts are circular to ovoid in outline; slightly yellowish or 

 greenish and refractile; 40-60/i in diameter; cyst wall made up of 2 

 membranes; cytoplasm hyaline; macronucleus and a contractile 

 vacuole are usually seen. 



This ciliate lives in the colon and caecum of man and causes 

 balantidiosis or balantidial dysentery. Strong (1904) made the first 

 histological study of the infection. The organisms invade the tissues 

 and blood vessels of the mucosa and submucosa. At the beginning 

 there is hjq^eraemia with punctiform haemorrhages, and later vascu- 

 lar dilatation, round cell infiltration, eosinophilia, etc., develop in 

 the infected area. Finally deep-seated ulcers are produced. The bal- 

 antidial dysentery is usually of chronic type. It has a wide geograph- 

 ical distribution. In the United States a few cases of infections have 

 been observed in recent years. In the Philippine Islands, more cases 

 have been noticed than anywhere else. 



