be
interesting to trace the remarkable chain of coincidences by virtue of
which the discovery was made.

"The beds in question have been laid out in a small artificial lake fed
by a tiny streamlet which forms one of the numerous tributaries of the
River Cray. Its depth is greater than usual in the watercress-beds,
otherwise the gruesome relics could never have been concealed beneath
its surface, and the flow of water through it, though continuous is
slow. The tributary streamlet meanders through a succession of pasture
meadows, in one of which the beds themselves are situated, and here
throughout most of the year the fleecy victims of the human carnivore
carry on the industry of converting grass into mutton. Now it happened
some years ago that the sheep frequenting these pastures became
affected with the disease known as 'liver-rot'; and here we must make a
short digression into the domain of pathology.

"'Liver-rot' is a disease of quite romantic antecedents. Its cause is
a small, flat worm--the liver-fluke--which infests the liver and
bile-ducts of the affected sheep.

"Now how does the worm get into the sheep's liver? That is where the
romance comes in. Let us see.

"The cycle of transformation begins with the deposit of the eggs of the
fluke in some shallow stream or ditch running through pasture lands.
Now each egg has a sort of lid, which presently opens and lets out a
minute, hairy creature who swims away in search of a particular kind of
water-snail--the kind called by naturalists _Limnoea truncatula_. 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 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
un