TRICHINA 77 



The liver fluke is a parasitic flat worm which each year 

 causes the death of many sheep by injuring their livers. 1 

 Like some other parasitic animals the liver fluke requires 

 two hosts to complete its development. The hosts of the 

 fluke are the sheep and certain snails. The adult liver 

 flukes form eggs and sperms in the liver of the sheep. 

 The fertilized eggs par- 

 tially develop in the 

 sheep ; then as embryos 

 they pass down the bile 

 duct into the intestine 

 and then out of the 

 body. 



The ciliated (sil'i-a-ted) larva then makes its way into 

 water or along dew-covered grass. If it comes in contact 

 with a water snail in the water or a land snail on the grass, 

 it enters the body of its second host, otherwise it dies. 

 Once inside the body of the snail it completes a compli- 

 cated development. By a bud-like process many young 

 flukes are formed which finally emerge from the snail and 

 make their way to the grass stems on which they encyst 

 themselves. If this grass is eaten by a sheep, the diges- 

 tive fluids set free the young fluke which goes up the bile 

 ducts to the liver, where it grows to maturity. 



66. Trichina. — Another unsegmented worm that is of 

 economic importance is the Trichina (tri-klma), now gen- 

 erally called Trichinella (tri'ki-neTla). This worm lives 

 in the intestine of mammals and from the intestine mi- 

 grates into the muscles of its host. In the muscle it 

 becomes encysted and remains until the flesh is eaten by 

 some other mammal. When pork, infected with this 

 parasite and insufficiently cooked, is eaten by man the 



1 The Animal Parasites of Sheep. Dr. Cooper Curtice. Bureau Animal 

 Industry, United States Department of Agriculture, 1890. 



