CHAPTER XXVII. THE LIVER-FLUKE (Fasciola hepatica 

 or Distomum hepaticum) : A PARASITIC METAZOAN. 



1. Form and Habitat. The well-known and unfor- 

 tunately abundant liver-fluke is a flat worm belonging to 

 the class of Trematodes. In its adult state it fives 

 chiefly in the bile-ducts of the sheep, but occurs also 

 occasionally in other mammals and even in man. It is 

 flat and leaf -like in shape, tapering to a point posteriorly, 

 and having a triangular projection at its blunt anterior 

 end. At the end of this projection is the mouth, and a 

 short distance from this anterior end, on the ventral surface, 

 is a sucker which is entirely superficial and has no connec- 

 tion with the interior of the body. The name of the group 

 to which the animal belongs, Distomidae, is derived from 

 tKe mouth and sucker, regarded as two suckers or two 

 mouths (di, two, and stoma, mouth), the word stoma being 

 used in the names of Trematodes in reference to the suckers 

 which are so characteristic of their structure. The mouth 

 in the Distomidae, however, has little claim to the title of 

 sucker. 



2. Size and Structure. The liver-fluke is about one 

 inch in length. The body consists externally of a body 

 wall consisting of a homogeneous cuticle on the outer 

 surface, with two layers of muscle-fibres an outer circular 

 layer and an inner longitudinal layer. An epidermis of 

 the usual character is wanting, but there are numerous 

 unicellular glands which open on the external surface. 

 Internally the substance of the body consists of a peculiar 

 kind of connective tissue which fills up the intervals 

 between the organs. There is no spacious, continuous 

 body cavity. The mouth leads into a pharynx formed of 

 muscular walls, acting as a sucking bulb, and this leada 



355 



