CHAPTER XIII 



PLATYHELMINTHES 



The Liver 

 Fluke : 

 External 

 Features. 



Sheep which are fed in damp meadows are liable to a 

 serious and usually fatal disease known as 

 " liver rot," in which the wool falls off, dropsical 

 swellings appear, and the animal wastes away. 

 This has been found to be caused by a parasite 



known as the Liver Fluke, Distomum hepaticum, which 



lives in the bile ducts of the sheep 



and sometimes of other animals, 



including occasionally man. It is a 



flat, brownish worm, about one inch 



long by half an inch broad, shaped 



liked a leaf with a blunt triangular 



projection at the broader end. At 



the tip of this projection lies the 



mouth, in the midst of an anterior 



sucker, and just behind the projection 



an imperforate posterior or ventral 



sucker is placed in the middle of the 



ventral side and serves as a means 



of attachment. Nearly midway be- 

 tween the suckers is a smaller genital 



opening, at the hind end of the body 



is a minute excretory pore, and on the 



dorsal surface at about a third of the length of the animal 



from the front end lies the opening of the Laurer-Stieda 



canal presently to be mentioned. The body is covered 



with a so-called cuticle, in which little backward-pointing 



spinules are embedded. 



The mouth leads into an ovoid, muscular pharynx, from 



which a short oesophagus passes backwards to divide before 



the posterior sucker into right and left branches or intes- 



Fig. 



121. — The Liver 

 Fluke. 



jf.o., Genital opening; «/., 

 mouth; v.s., ventral 

 sucker. 



