348 ENTOZOA. 
CLASS Ii. 
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ENTOZOA, Rud. 
The Entozoa or Intestinal Worms are remarkable, because 
the greater number inhabit the interior of other animals, and 
there only can propagate. There is scarcely a single animal 
that is not the domicil of several kinds, and those which are 
observed in one species are rarely found in many others. 
They not only inhabit the alimentary canal and the ducts that 
empty into it, such as the hepatic vessels, but even the cel- 
lular tissue, and the parenchyma of the most completely in- 
vested viscera, such as the liver and brain. 
The difficulty of conceiving how they get there, added 
to the fact of their never having been seen out of living 
bodies, has induced some naturalists to believe that they 
are spontaneously engendered. We now know that most of 
them not only evidently produce ova or living young ones, 
but that in many, the sexes are separate, and coition ensues as 
among other animals. We are then compelled to believe, that 
they propagate their race by germs sufliciently minute to be 
transmitted through the narrowest passages, and that frequently 
those germs are contained in animals at birth. 
In the Intestinal Worms we find neither trachee, nor any 
other organ of respiration, and they must receive the influ- 
ence of oxygen through the medium of the animal they inha- 
bit. They present no trace of a true circulation, and we merely 
