310 SOME COMMON INTERNAL PARASITES [CH. IX 



eggs of the parasite are present ; and to slaughter badly 

 infected individuals. 



It will not be out of place to draw attention to the 

 losses suffered in past years by the ravages of the Liver- 

 fluke, and to the value of exact zoological knowledge in 

 enabling us to combat the disease. In 1830 sheep to 

 the value of four millions sterling were lost by "rot" in 

 England alone. In 1879-80 about double that amount 

 perished from the same cause. In Ireland during 1862 

 sixty per cent, of the flocks were fatally affected. Of 

 recent years, since Thomas's researches have made known 

 the life-history of this pest, outbreaks have not been so 

 serious. 



Of other Trematodes we will mention but three, which 

 are parasite in birds. Monostoma mutabile is found in the 

 suborbital sinuses, nasal cavities, trachea, air-sacs, and 

 intestines of aquatic birds and occasionally of others. Its 

 redia stage is almost certainly passed in some small snail. 



M. flavum occurs in the trachea and oesophagus of 

 duck and other lamellirostrate birds. The intermediate 

 host is the snail Planorbis corneus. 



Notocotyle verrucosum becomes sexually mature in the 

 intestine of fowls, ducks, geese and other birds. Its 

 intermediate host is not known with certainty, but is 

 probably a snail of the genus Planorbis or Limncea. 



Cestodes (Tapeworms). 



These flat-worms though outwardly exhibiting an 

 apparent segmentation are usually, for reasons which are 



