66 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 



out of the body 



Fig. 31. — Rediaform 

 of fluLeworm as it 

 appears in the body 

 of the snail, show- 

 ing eercarise. After 

 Leuckart. 



Fig. 33. — Head of 

 tapeworm showing 

 suckers and hooks. 

 Greatly enlarged. 



of the snail, crawls up the stem of a 

 plant or blade of grass and secretes 

 about itself a cyst or hard film of gela- 

 tinelike substance. In these situations 

 it is eaten by the grazing sheep. In the 

 stomach of the sheep the cyst is dis- 

 solved, and the imma- 

 ture worm soon works 

 its way to the Uver, 

 where it grows and be- 

 comes mature, thus com- 

 pleting the life history. 



Tapeworm. ^ There 

 are several species of 

 tapeworms, all of which 

 are parasitic in their 

 adult stages, in the 

 bodies of vertebrates, as, 

 man, cattle, dog, sheep, 

 birds, fishes, etc. At Fig 

 least three different spe- 

 cies are fairly common 

 as parasites in the in- 

 testines of man, but we 

 shall speak of only one 

 here, namely, the pork tapeworm.* 



Like the flukeworm, the tapewordi 

 passes the larval stage of its life history 

 in one animal and the adult stage in 



32. — Cercaria 

 form of flukeworm. 

 In this form it 

 escapes from the 

 snail's body, climbs 

 ablade of grass, and 

 becomes encysted. 

 After Leuckart. 



' Dr. Charles Wardell Stiles says that the pork tapeworm is comparar 

 tively rare in this country, and that the beef tapeworm is the most 

 common one here. Bull. 19, U. S. Dept. Agri. B. A. I., 1898. 



