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 (Disto?na), a member of this class. 
Class II.— Nematelminthes. 
The Round, or Thread, Worms include free forms, as 
the Yinegar-eel; parasitic forms, as the Pin-worm and 
Trichina; and forms 
free when 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 Trichinae become 
sexually mature in the 
intestines. The young 
are produced and bur- Fio. 21S.— Trichina spiralis: I, male; a, mouth; 
* . c, intestine; II, capsules, with Trichin® in mus* 
TOW their way into the cle, much enlarged. 
