CHAPTER XXIV 



PARASITIC INFUSORIA IN GENERAL 



By 



Robert Hegner 

 The Johns Hopkins University School of Hygiene and PubHc 



Health 



Although most of the infusoria are free-living in habit a 

 number of parasitic species occur in each of the larger groups. 

 Problems and methods of study with respect to the genus Balan- 

 tidhim and the opalinid^ w^ill be found in the two following 

 chapters. Most of the protozoa that occur in the stomach of rumi- 

 nants are ciliates ; these are described in Chapter VI. Information 

 regarding certain species of ciliates is also presented in several 

 other chapters ; the reader will find references to these in the 

 index. Recent accounts of the morphology and classification of the 

 infusoria are presented in Wenyon's Protozoology (1926, pp. 

 1 153-1229) and in Calkins' Biology of the Protozoa (1926, pp. 

 363-401). Calkins has also included a key to the genera of 

 INFUSORIA (pp. 401-414). Wenyon's account deals largely with 

 parasitic forms whereas Calkins includes both free-living and para- 

 sitic species. 



Authorities dififer with respect to the classification of the 

 INFUSORIA. As a rule the group is divided into two sections, the 

 ciLiATA and the suctoria. Wenyon follows Metcalf in dividing 

 the group into the protociliata, containing the single family 

 OPALiNiD.E which are all parasitic, and the euciliata containing 

 the CILIATA and suctoria. Four orders are usually recognized in 

 the section ciliata. The following paragraphs are intended to 

 indicate in brief to what groups the parasitic ciliates available for 

 study belong and in what types of animals one may expect to find 

 them. 



The family opalinid^ belongs either in the suborder astomina 



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