260 



CIVIC BIOLOGY 



Undulating 

 \ /Membrane 



Flagellum 



Trypatwsoma gambiense, which has long been the scourge of the west 

 coast of Africa and is now spreading rapidly up the Congo, is the para- 

 site of sleeping sickness in man. It is found in the blood of a number 

 of native animals and is carried to man by the bite of one of the tsetse 

 flies, Glossina palpalis. 



The flatworms, flukes, and tapeworms Platyhelminthes 

 (platys, "flat"; helminthes, "worms"). The flatworms 

 comprise a group of diverse forms which vary in size from 



almost microscopic 



Nucleus flukes to tapeworms 



60 feet in length. 

 Two large classes, 

 the trematodes (to 

 which the flukes 

 belong) and the 

 cestodes (to which 

 the tapeworms be- 

 long) contain only 

 forms that are par- 

 asitic on or in other 

 animals. Two hosts 

 are commonly re- 

 quired for one of 

 these parasites to 



complete its life cycle, which depends on the practice, com- 

 mon among animals, of eating one another raw. So, in parts 

 of the world where fish, pork, beef, and other meats are com- 

 monly eaten raw, man comes in for his full share of these 

 parasites. People with raw-flesh-eating habits, coming to us 

 from the ends of the earth, bring their internal pets with 

 them 1 and proceed to take up a collection of American 

 forms. The eggs are minute, and flies swallow them and 



FIG. 112. Trypanosoma gambiense, from a case of 

 sleeping sickness, different forms 



After Manson 



1 A tapeworm has been known to live in man for thirty-five years. 

 BRA UN 



