PHYLUM NEMATOIDEA 187 



beard poorly developed; perverted appetite for clay, dirt, 

 etc.; dropsical condition, and other peculiarities. The 

 Rockefeller Sanitary Commission has agents throughout the 

 southern states who are trying to better conditions among 

 the poorer people by treatment and by instruction as to 

 proper methods of living. In many districts the shiftless- 

 ness of the population is largely due to the prevalence of 

 hook-worm. Ninety per cent, of the people in some 

 counties in Louisiana have this parasite. I 



Another very injurious round-worm is trichina, Trichinella 

 spiralis, which lives in rats, hogs, men, and a few other 

 animals. This parasite may be acquired only by eating 

 flesh containing the encysted larvae, but if meat is 

 thoroughly cooked there is no danger of infection. Other 

 important human parasites are the pin-worm and the whip- 

 worm, which live in the intestine; and the filaria worms 

 which inhabit the blood and lymph vessels. The latter 

 cause a horrible disease known as elephantiasis, in which 

 the legs and other parts of the human body become greatly 

 enlarged. They occur only in tropical countries, and are 

 transmitted by the bites of certain mosquitoes. There are 

 many round-worms which cause diseases in animals and 

 plants. Tylenchus tritid is an important plant parasite 

 which produces gall-like growths on the roots of tomatoes 

 and other plants. 



CLASS 2. GORDIACEA 



These worms (Fig. 78, A) are commonly known as horse- 

 hairs, horsehair worms, and horsehair snakes, on account of 

 their hair-like form, and there is a belief among ignorant 

 persons that horsehairs will turn into worms if kept in 

 water. They are often very numerous along the shores of 

 ponds and streams during their breeding season. At such 

 times they wrap about each other in great bunches, forming 

 veritable "Gordian knots " (whence the name of the class). 

 Sometimes the adult worms get into man and live for a time 

 as parasites. 



