66 



FLATWORMfS, KUUNDWORMa, AND RriTIFERS 



out of the body of the snail, crawls up the stem of a 

 plant or blatle of grass and secretes 

 aliout itself a cyst or hard film of gela- 

 tinelike substance. In these situations 

 it is eaten Ijy the grazing sheep. In the 

 stomach of the slieep the cyst is dis- 

 solved, and the imma- 

 ture worm soon works 

 its way to the liver, 

 where it grows and be- 

 comes mature, thus com- 

 pleting the life history. 

 Tapeworm. — Tliere 

 are several species of 

 tapewomis, 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 connnon 

 as parasites in the in- 

 testines of man, but we 



Fig . .3 1 . — Redia form 

 of fluUeworm as it 

 appears in the body 

 of ttie snail, .show- 

 ing cercarite. After 

 Leucliart. 



Fig. 3.3. — Head of 



tapeworm showing 

 suckers and liooks. 

 Greatly enlarged. 



.32. — C'ercaria 

 form of fiiike\\oriu. 

 In thi.s form i* 

 esca].>cs from the 

 snail's bod}-, climbs 

 a bl ade of grass, and 

 becomes encysted, 

 shall speak of only one After Leuckart. 



here, namely, the pork tapeworm.' 



Like the flukeworm, the tapeworm 

 ]3asses the larval stage of its life history 

 in one animal and the a(hilt stage in 



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

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

 common one Itere. Bull. 19, U. S. Dept, Agri. B. A. I., 189S. 



