34 



Chapter III. 



THE LIVER-FLUKE OF THE SHEEP. 



Fasciola (Distomum) hepatica. 



The adult liver-fluke is a flat unsegmented worm, about an 

 inch and a half long, living in the bile-ducts of certain 

 domestic animals, and notably in those of the sheep, in which 

 it gives rise to the destructive disease known as liver-rot. It 

 very rarely occurs in man. 



The animal is hermaphrodite, and its eggs, which have 

 thick chitinous shells, are deposited in enormous numbers 

 in the bile-ducts of the sheep or other host, from which 

 they pass into the alimentary canal, ultimately escaping with 

 the faeces. From these fertilised eggs, if deposited in damp 

 places or in water, larvae are produced which lead a free exist- 

 ence for a short time, but very soon become parasitic within 

 the body of Limncea truncatula, an amphibious snail. Two 

 or more generations produced by development of unfertilised 

 ova now succeed : and the last of these encyst on grass. These 

 encysted forms are swallowed with the grass by sheep, and 

 passing into their bile-ducts become the adult sexually mature 

 flukes. 



This alternation of generations is entirely different from 

 that of Obelia. 



I. THE MATURE LIVER-FLUKE. 



Slit open the bile-ducts in the liver of an infected sheep, 

 and transfer the living flukes to a dish of warm salt-solution 

 (75 per cent.) to clean them. 



1. Inject the excretory system of one fluke, and the alimentary 



