PHYLUM PLATYHELMIA 



181 



found in the intestine of the animal which eats the herbi- 

 vore. There are species which have their cycles between: 

 pig and man, cow and man, fish and man, mealworm and 

 rat, flea and dog, rabbit and wolf, etc. 



The life cycle of the common beef tapeworm is shown in 

 Fig. 75. An adult (A) in a man's intestine is continually 

 giving off ripe proglottids (B) which pass out and shed 

 eggs (C) upon the ground. A single proglottid may 

 produce several thousand eggs, and the contamination of 



HOST 



FIG. 75. Life history of beef tapeworm. A, adult tapeworm in intestine of 

 man; B, proglottid full of eggs on ground; C, eggs on ground; D, six-hooked 

 larva (onchophore) set free and bores through tissues of cow; E, cysticercus, or 

 bladderworm, in cow's flesh; F, young tapeworm in man. 



the food of cattle is therefore easily accomplished. A ripe 

 egg contains a little 6-hooked embryo (D) which is freed 

 from the egg shell in the cow's intestine and at once 

 bores out into the body. In the liver, or the muscles, it 

 comes to rest and undergoes a complete reorganization. 

 After three months a cysticercus, or bladder- worm (E), 

 has developed and the cow 's flesh may then infect man with 

 tapeworms. The cysticercus is a little bladder with an in- . 



