The Rot in Sheep. 



35 



least, of the entozoa underwent regular metamorphoses, and 

 that hydatids and tape-worms had a necessary and mutual 

 dependence on each other. It could not be expected that in- 

 vestigations 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 trans- 

 formations. Among this number the liver-fluke may be placed, 

 the structure and metamorphoses of which we shall now attempt 

 to describe, for it is upon knowledge of this kind that the 

 means are based which, as pathologists, we possess for the treat- 

 ment and prevention of the rot in sheep. 



Technically speaking, the liver-fluke is known as the 



Distoma hepaticum, or Fasciola hepatica. 



The distoma belongs to the order Tremadota, which denotes 

 that it is a suctorial worm. By most naturalists it is placed 

 in the second family of this order. The name Fasciola, to which 

 many naturalists give preference, was originally bestowed on the 

 entozoon by Linnaeus ; 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, 

 fig. 3), and a second a little behind the first named, on the 

 ventral surface (/;, fig. 3). The term hepaticum is employed 

 in conjunction with Distoma to signify that the entozoon is 

 met with in the liver. It will thus be seen that it is a matter of 

 minor importance whether we speak of the entozoon as a liver- 

 fluke, trematode worm, distoma, or fasciola. 



Professor Owen, in his 6 Lectures on the Invertebrate Animals ' 

 (1843), says: "The Trematoda inay be 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 Linnaeus, adopted 

 external and easily recognisable characters lor the generic sub- 

 divisions of the Trematode order according to the numbers and 

 positions of the suctorious orifices and cavities. " W hen there 

 is only a single one, it constitutes the genus Monostoma ; when 

 there are two, which are terminal or at opposite ends of the 

 body, you have the character of the genus Ampkistoma ;* when 



* The fluke thus named is frequently met with in oxen mid slice]), attached to 

 the mucous surface of the rumen, in which situation it appears in this country t at 

 least, to be productive of little mischief.— Ai thor. 



i) 2 



