FLATWOKMS, UOUiS"DWORMS, AND ROTIFERS 



69 



resemble hairs that some people think they are transformed 

 horse hairs. The guinea ^vorm, which is a parasite of 

 man in tropical countries and 

 which sometimes attains a length 

 of several feet, is a member of 

 the group of roundworms. 



Trichinella spiralis. — This is 

 one of the most important round- 

 worms, economicall}'' speaking, in 

 the United States. The adult 

 worm is very small, scarcely vis- 

 ible to the iraked eye, and is 

 fomid only in the intestines of 

 mammals, as, man, pig, rat, etc. 

 It is probable that the pig be- 

 comes infested with this worm 

 by eating the 

 flesh of some 



animal, as the rat. Of course man be- 

 comes infested Is}' eating raw or half- 

 cooked pork. In this way the worms, 

 in a larval condition, are taken into the 

 alimentary canal. There they soon be- 

 come mature, and the young are produced 

 in immense numbers. These soon work 

 their way through the walls of the intes- 

 tines and finally reach the muscles 'Fig. 

 37), where they become surrounded with 

 a cyst, and there they remain. Before 

 FiG.37.— Tnchineiia forming the cyst, the embryos feed upon 

 spiralis imbedded |.j^g muscular tissue, causiug scrious com- 

 AfterTeu'^kTrt^" " phcations that often result in the death 



Fig. 36. — Hairworm. 



