Nemathelminthes. 351 



CLASSES OF PLATYHELMINTHES. 



[Class i. Trematoda Liver Fluke. 

 Platyhelminthes. .-j Class 2. Turbellaria (ciliated). 

 [ Class 3. Cestoda Tapeworm. 



BRANCH NEMATHELMINTHES. 



THE ROUNDWORMS. 



The roundworms have long, cylindrical bodies. They 

 are not segmented, but some of them have the appear- 

 ance of segmentation. Some are parasites in animals and 

 plants, while others live a free life. Most of the round- 

 worms belong to the class Nematoda. 



Hair Worms. These are often found as parasites in 

 grasshoppers and other insects, but later they live free 

 outside. They are by many ignorant people believed to 

 be horsehairs that have 

 "come to life" by soaking 

 in water. 



The Vinegar Eel. This is 



another small roundworm 



. . , . FIG. 198. HAIR WORM. 



which is well known. 



Intestinal Worms. Two forms of roundworms are not 

 uncommon in the human intestine, especially in those of 

 children. The eggs or larvae have been swallowed with 

 food. The pinworm is well known ; it is small and white 

 and usually inhabits the rectum. The other is larger, 

 sometimes somewhat resembling an earthworm in size and 

 general appearance, though lacking the segments. It 

 belongs to the genus Ascaris. 



Trichina. The most dangerous of the parasitic round- 

 worms is Trichina. It is small, not exceeding an eighth 



