CHAPTER XX 

 THE ROUNDWORMS 



The unsegmented roundworms (phylum Nemathelminthes , 

 Fig. 101) are much more important to man than the segmented 

 annelids, since many of them live as parasites in the bodies of 

 human beings. The roundworms that are most easily obtained 

 are the vinegar " eels." These minute worms are abundant in 

 moldy vinegar, and when examined under the microscope, give 

 one a very good idea of what a roundworm looks like. They 

 are not injurious, and no one need be afraid to use vinegar con- 

 taining them. 



" Horsehair Snakes." — Sometimes long, slender animals 

 are found wriggling about in watering troughs or in pools of 

 water, and because of their resemblance to a horsehair are 

 known as " horsehair snakes." By many they are thought 

 to be horsehairs that have become alive, but this is, of course, 

 absurd, for horsehairs placed in water will never change into 

 worms. The name Gordius has been applied to these animals 

 because they are often tangled up like the Gordian knot which 

 Alexander the Great severed with his sword so long ago. The 

 young spend part of their lives as parasites in the bodies of 

 aquatic insects. When these insects are devoured by other 

 animals, the worms are liberated in their intestines, where they 

 live until full grown and then escape into the water. 



Intestinal Parasites. — Several kinds of roundworms may 

 occur in the intestines of human beings, especially children. 

 Some of these, also called threadworms, are from one-fourth to 

 one-half inch long and look like white cotton threads. Others 

 are reddish-white in color and much longer — from four to 



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