44 



THE WORMS, 



fluke-worm, F, that finally escapes through the intestine, 

 and lays eggs in pools or ponds, thus completing the trans- 

 formation, that varies in different genera. The tape-worm 

 that comes from pork belongs in this class. 



FIG. 42. A, Monostomum mutabile. A, the ciliated embryo ; a, the nurse ; 

 6, nurse free ; C, Redia of Distoma pacificum, containing germs of 

 other Redice ; D, Redia containing Cercarice (a) ; E, Cercaria ; F, Dis- 

 toma, which results from the metamorphosis of the Cercaria. (After 

 Steenstrup.) 



Class II. ROUND OR 

 THREAD- WORM (Nema- 

 telminthes). 



The pin-worm and Trichina 

 are examples. The Trichina 

 spiralis (Fig. 43), one twelfth 

 of an inch long, is the most 

 dangerous, becoming encysted 

 in the human muscles. The 

 eggs are eaten by rats, that in 

 turn are perhaps eaten by pigs, 

 so finding their way into the 

 human system. The Gordius 



FIG. 43. Trichina. 



