96 
Tlie Rot ill Sheep. 
in which its ova were alone perfected, woukl, if given to sheep, 
produce hydatids in the brain. Nor was this the only proof 
adduced in corroboration of the statement, for it was said that 
the converse was equally true — namely, that tape-worms were 
quickly developed in the intestines of the dog, by giving to this 
animal the so-called heads of the cwnuras. 
A number of experimenters was thus called forth, in various 
parts of the Continent in the first instance, and afterwards in 
England, every one of whom confirmed the conclusions arrived 
at by Siebold. It was thus proved beyond disputation that some, 
at least, of the entozoa underwent regular metamorphoses, and 
that hydatids and tape-worms had a necessary and mutual depend- 
ence on each other. It could not be expected that investigations 
of this kind would end here, and it has since been shown that 
very many entozoa pass through far more complex changes than 
the tape-worm ; and that they often exist out of the bodies of the 
animals which they ultimately inhabit, in such peculiar forms, 
and for so long a time, as almost to set at nought the efforts of the 
helminthologist to unravel their several transformations. Among 
this number is the liver-fluke, the structure and metamorphoses 
of which we shall now attempt to describe, as it is upon know- 
ledge of this kind that the means which, as pathologists, we possess 
for the treatment and prevention of the rot in sheep are based. 
Technically speaking, the liver-fluke is known as the 
Distoma hepaticum, or Fasciola hepatica. 
The name Fasciola, to which many naturalists give preference, 
Avas originally bestowed on this entozoon by Linna;us, while that 
of Distoma was adopted by Retzius, under the belief, as would 
seem, that it was furnished with two distinct mouths — one at 
the anterior extremity (a, Jiff. 3), and a second a little behind the 
first named, on the ventral surface (h,Jig. 3). The term hepaticum 
is employed in conjunction with Distoma to signify that the 
entozoon is met with in the liver. 
The distoma belongs to the order Trematoda, a classification 
which denotes that it is a suctorial worm, and by most naturalists it 
is placed in the second family of this order. It will thus be seen 
that it is a matter of minor importance whether we speak of the 
creature as a liver-fluke, trematode worm, distoma, ox fasciola. 
Professor Owen, in his '■Lectures on the Invertebrate Animals^ 
(1843), says: " The Trematoda maybe characterised as having a 
soft, rounded or flattened body, with an indistinct head, pro- 
vided with a suctorious foramen, and having generally one or 
more sucking cups for adhesion in different parts of the body ; 
the organs of both sexes are in the same individual." From the 
same author we learn that Rudolphi, a pupil of Linna'us, adopted 
