VERMES. 



265 



which are really reproductive joints. It develops from 

 the egg in the digestive canal of the Pig, burrows into 

 the cellular tissue of the animal, and there becomes en- 

 cased. It thus causes the disease " measles." If the pork 

 be eaten by man, in an uncooked condition, this case is 

 dissolved by the gastric juice, and the embryo develops 

 into the Tape-worm, attaching itself to the intestine by 

 its "head," and budding off the reproductive segments. 

 As these become ripe and filled with fertilized eggs, they 

 are detached, and pass off with the excrement. 



The disease called " rot," in Sheep, is produced by the 

 Fluke (Distoma), a member of this class. 



Class II. — Nematelminthes. 



The Kound, or Thread, Worms include free forms, as 

 the Vinegar-eel; parasitic forms, as the Pin-worm and 

 Trichina ; and forms 

 free w T hen adult, and 

 parasitic when young, 

 as the Hair-worm (Gor- 

 dius). 



The Trichina is usu- 

 ally derived by Man 

 from the flesh of the 

 Pig. It exists in the 

 muscles, enclosed in mi- 

 croscopic cases. If the 

 meat be eaten uncooked 

 or partially cooked, the 

 cases are dissolved, and 

 the Trichinse become 

 sexually mature in the 

 intestines. The young 



are produced and bur- Fig. 21S. — Trichina spiralis: I, male; a, mouth; 



, -i . . , . , c, intestine ; II, capsules, with Trichinae in mus- 



rOW their way into the cle, much enlarged. 



