1922] McDonald: On Balantidium coli and Balantidium suis 249 



The wide diversity of hosts, ranging from hydroids and crustaceans 

 to the warm-blooded vertebrates, including man, must demand a wide 

 versatility on the part of the parasite. Considerable structural varia- 

 tion is apparent even on cursory examination, and some of these 

 structural differences might be sufficiently marked to servTT for generic 

 differentiation. A new generic division would seem desirable, but the 

 suggestions of Biitschli (1884) and Schweier (1900) in this direction 

 have not been generally accepted. 



BALANTIDIUM COLI MALMSTEN (1857) 



SYNONOMY: 



Paramoecium (?} coli Malmsten, 1857. 

 Plagiotoma coli, Claparede and Lachmann, 1858. 

 Leucophyra coli, Stein, 1860. 

 Holophyra coli, Leuckart, 1861. 

 Balantidium coli, Stein, 1862. 



Up to the present time only one species, Balantidium coli, has been 

 described as parasitic in pigs. It was first described by Malmsten 

 (1857) who, noting its likeness to Paramoecium colpoda (Ehrenberg), 

 suggested the name Paramoecium (?) coli. During the following year, 

 Claparede and Lachmann (1858) reproduced one of Malmsten 's orig- 

 inal figures and after considering his description transferred the 

 species to the genus Plagiotoma. In 1860, Stein, using the description 

 by Malmsten (1857), pointed out that the organism was not a Para- 

 moecium and Relieved that it properly belonged in the genus Leuco- 

 phyra. Leuckart in 1861 discovered a ciliate in the intestine of pigs 

 which he concluded was identical with the one already described, but 

 he was not satisfied with the genus to which it had been assigned by 

 Stein (1861) and believed that its closest relation was with Holophyra 

 in which genus it should be placed. In. 1863 he still retained this view 

 but suggested the appropriateness of the establishment of a new genus. 

 But Stein (1862) had already recognized those characters of the 

 species which showed its close relation to Balantidium entozoon and 

 had placed it in the genus Balantidium. 



During the present investigation the following specific character- 

 istics have been found very constant. The individuals of the species 

 Balantidium coli are ovoid in form, the more pointed end being an- 

 terior; length varies from 30/* to 150/t; breadth varies from 25,/A to 

 120ju, ; in the majority of individuals the length is 1.3 times the breadth ; 

 the greatest transverse diameter intersects the longitudinal axis poster- 



