If he
finds a snail, he bores his way into its flesh and soon begins to grow
and wax fat. Then he brings forth a family--of tiny worms quite unlike
himself, little creatures called _rediae_, which soon give birth to
families of young _rediae_. So they may go on for several generations,
but at last there comes a generation of _rediae_ which, instead of
giving birth to fresh _rediae_, produce families of totally different
offspring; big-headed, long-tailed creatures like miniature tadpoles,
called by the learned _cercariae_. The _cercariae_ soon wriggle their
way out of the body of the snail, and then complications arise: for it
is the habit of this particular snail to leave the water occasionally
and take a stroll in the fields. Thus the _cercariae_, escaping from the
snail, find themselves on the grass, whereupon they promptly drop their
tails and stick themselves to the grass-blades. Then comes the
unsuspecting sheep to take his frugal meal, and, cropping the grass,
swallows it, _cercariae_ and all. But the latter, when they find
themselves in the sheep's stomach, make their way straight to the
bile-ducts, up which they travel to the liver.
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