42 



ZOOLOOT. 



eaten by the hog are developed in its body into the larval 

 tape-worm (called in this species Cysticercus cellulosm, Fig. 

 42). The liead with its suckers is formed, and the body 

 becomes flask-shaped; the Cysticerci then 

 bury themselves in the liver or the flesh of 

 I pork, and are transferred living in uncooked 

 pork to the intestines of man. The body 

 now elongates and new joints arise behind 

 [ the head until the foim of the tape-worm is 

 I attained, as in Fig. 41. 



The hinder joints then become filled with 



I eggs and break oil, becoming independent 



joints comparable with the "parent-nurses" 



of the Cercarias, except that they are not 



contained in the body of the Tjenia (as in 



Fia42.-c»s««r- ti^g Cercaria), but are set free. The inde- 



cus, or larval ' 



Tape-worm, pendent joint is called a "proglottis." It 

 escapes from the alimentary tract of its human host, and 

 the eggs set free, in and about privies, are swallowed by 

 that unclean animal, the pig, and the cycle of generations 

 begins anew.* 



Class II. — Nematelminthes {Round- or Tliread-worms). 



General Characters of Round-worms. — In these worms the 

 body is round and tlircud-like, not being jointed. Many 

 are parasitic: such are the Ascarids. 



The round-worm most dangerous to human life is the 

 Trichina ftpiralis (Fig. 43). It is very minute, tlie female 

 being 3mm. in length, and tlie male worm half as long. The 

 female is capable of producing a thousand young. The 

 eggs are eaten by rats, dead rats are sometimes devoured by 

 pigs, and jiork thus infested when e.'iten by man, either 

 raw or partly cooked, often causes the death of their hu- 

 man host. 



The hair-worms (Gordiiis aquaticiis. Fig. 44) resemble a 

 piece of a horse's hair, and are so-called because they are 



