WORMS. 



245 



Other vertebrates than man possess tapeworms. The cat 

 gets hers from the mouse, the dog his from cattle and rab- 

 bits, the sharks from other fish, etc. 



CLASS II. KEMATHELMINTHES. 



In these round-worms the body is long and cylindrical, 

 and is covered with a firm cuticle. Usually both mouth 

 and vent are present, but there is never any division of the 

 body into segments. Some live freely in the water, some 

 are parasitic in plants, and some infest animals. Among 

 them are to be mentioned the vinegar and paste "eels," 

 which are occasionally found in these substances. Here, 

 too, belong the " horsehair- worms," which are frequently 

 believed to be horsehairs converted into worms by soaking 

 in water. These hairworms are at one period of their 

 lives parasitic in insects, especially in grass- 

 hoppers. Some of the roundworms occur 

 as parasites in man. The stomach- worms 

 and pinworms of children belong to the 

 round-worms, and these obtain entrance to 

 the human system only as the exceedingly 

 minute eggs are taken into the stomach 

 by way of the mouth. 



Worst of all the parasitic Nemathel- 

 minthes is the Trichina, which when adult 

 is scarcely an eighth of an inch in length, 

 and yet which not infrequently causes 

 death. Man is usually infected with them 

 by eating raw or partially cooked pork. In 

 the pig they first appear in the alimentary 

 canal, where the mothers bring forth myri- encysted in hul 



, . . . man muscle. Af- 



ads oi living young. These young burrow ter Leuckart. 

 outwards into the muscles and there enclose themselves in a 



