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. 
Fic. 42.—A, Monostomum mutabile. A, the ciliated embryo; ¢, the nurse ; 
6, nurse free; C, Redia of Distoma pacificum, containing germs of 
other Redze ; D, Redia containing Cercari@ (a); E, Cercaria; F, Dis- 
toma, which results from the metamorphosis of the Cercaria. (After 
Steenstrup.) 
Class II].— ROUND OR 
THREAD-WorRM (Nema- 
telminthes). 
The pin-worm and Trichina 
are examples. The TZyichina 
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 
Fic. 43.—Trichina. human system. The Gordius 
