ANIMAL PARASITISM 



43- 



are the human intestinal flagellate, Giardia lamhlia, and the blood- 

 inhabiting trypanosome, Trypanosoma rhodesiense, causative agent of 

 African sleeping sickness which is carried by the tsetse fly. Ex- 

 amples of parasitic Infusoria are the human intestinal ciliate, Balan- 

 tidium coli; the various species of Opalina, and related genera found 

 in the excretory bladder or cloaca of frogs and toads. Of the thou- 

 sands of species of Sporozoa, all of which are parasitic, probably the 

 best known are the three species of the genus Plasmodium, which cause 

 human malaria, and Babesia higemina, which produces Texas tick 

 fever of cattle. 



Fig. 182. — Tsetse flv, Glossina, the transmitting agent for trypanosoma. which 

 causes African sleeping sickness. (Reprinted by permission from Introduction to 

 Human Parasitology by Chandler, John Wiley and Sons, Inc.) 



Platyhelminthes.— This phylum also contains four classes, two of 

 which, Trematoda (flukes) and Cestoda (tapeworms), are all para- 

 sitic, while the other two, Turbellaria and Nemertinea, are mainly 

 free-living but contain some species which are parasitic on aquatic 

 invertebrates. Among the best known examples of Trematodes are 

 Fasciola hepatica, the sheep liver fluke; Clonorchis sinensis, the 

 Chinese human liver fluke ; and Schistosoma haematoUum, one of the 

 three species of human blood flukes. Probably the best known tape- 

 worms are Taenia saginata, the beef tapeworm. Taenia solium, the 

 pork tapeworm and DiphyUohothrium latum, the broad fish tape- 

 worm, all three common parasites of the human intestine, and Echino- 



