PLATYHELMIA 51 



been found also in the substance of the liver and are some- 

 times carried away in the blood stream to other parts of the 

 sheep. 



This account of the life-history goes to show why the 

 disease is common in wet districts and in wet seasons. The 

 descendants even from one ovum may amount to hundreds. 

 It is in the autumn in temperate conditions that the sheep 

 usually receive the infection of young flukes, and during the 

 winter the sheep indicate by well-known symptoms, even by 

 death, the effects. The eggs are discharged in large numbers 

 and are found in the faeces of the sheep. Draining wet land 

 has been proved to be an effectual method of prevention, and, 

 following the observation that salt 

 marshes are immune, applications 

 of salt have been found to be 

 beneficial. It is obvious also that 

 good will result from regulating the 

 movements of sheep so as to prevent 

 the eggs from developing, and the 

 sheep from infection. 



It is interesting to note that 

 the life-history was worked out 

 independently by Leuckart in Ger- Fro- 22.Limnaea truncatula. 

 many and by Thomas in England.' 



Taenia. Cestodes, or tape- 

 worms, are parasitic in vertebrates in their adult state, and 

 the young phase is also parasitic and is passed usually also 

 in a vertebrate, sometimes in an invertebrate, host. The 

 final host gets its infection by eating the intermediate 

 host, and the latter is infected by swallowing the eggs, or, 

 in the case of aquatic animals, from the larvae liberated by 

 the eggs. 



Some tapeworms are of economic importance. Thus 

 Taenia solium of man is obtained from measly pork. 

 Coenurus cerebralis, which is found in the dog, causes during 

 its young stage a disease in sheep called ' sturdy.' In this 

 case the intermediate stage is a coenurus characterised by the 

 development of a bladder possessing many heads or scoleces 



1 1881-82, Leuckart, Zool. Anz. ; 1882-83, Thomas, Jour. Agri. Sec. 



