VEKMES 



155 



Nemathelminthes or Threadworms 



The round worms differ from the Annulata in not show- 

 ing any external evidence of segmentation. Most of the 

 species live as parasites during part or all their lives. As- 

 caris is a genus containing several species which are often 

 present in the in- 

 testines of mam- 

 mals, and one spe- 

 cies is common in 

 the lungs of the 

 frog. Trichina, a 

 microscopic round 

 worm causing the 

 condition known 

 as measly pork, is 

 a dangerous para- 

 site to man. He 

 becomes infected 

 by eating affected 

 pork not well 

 cooked. In 1892, 

 the United States Department of Agriculture found over 

 seventeen thousand carcasses of hogs containing Trichina?. 

 A fuller discussion of parasitic worms is given in the chap- 

 ter on parasites. 



The vinegar eel (Anguillula) is a free living worm often 

 present in good cider vinegar. It is just large enough to be 

 recognized by the naked eye, and if a little vial containing 

 some vinegar be looked at toward the light as many as five 

 hundred may be seen squirming vigorously. They are 



FIG. 181. Ascaris lumbricoides : a parasite often 

 present in the intestine of children. Photograph, 

 natural size. 



