342 



APPLIED BIOLOGY 



This stage (called a bladder-worm or cysticercus) remains 

 for some time in the tissues; and if uncooked pork or beef 

 be eaten by man, an encysted bladder-worm may attach itself 

 to the wall of the intestine by means of its hooks and suckers 



and develop into a 

 tape-worm. 



The above ac- 

 count of the human 

 tape-worms, of 

 which one species 

 develops its larval 

 stage in pigs and 

 another in cattle, 

 represents the life- 

 history of all the 

 tape-worms which 

 inhabit the intes- 

 tines of various ver- 

 tebrates. Two hosts 

 are required, one for 

 the tape-worm, and 

 one for the interme- 

 diate bladder-worm 

 stage. One species 

 of tape-worm of 

 dogs has its bladder- 

 worm in rabbits ; 

 one of sea-gulls has 

 its in earth-worms ; and one of cats has its in liver of rats 

 and mice. In Oriental countries there is a large human 

 tape-worm whose bladder-worm stage is passed in certain 

 fishes. In a large number of cases, the bladder-worm stage 

 occurs in the particular animal which is a favorite food of 

 the animal which may be the host of the fully developed 

 worm. 



FIG. 108. Tape-worm, a, head; b, larval stage 

 found in flesh; c, parts of an adult worm from 

 intestine. (From Hatschek.) 



