DISTOMIASIS. 195 



family, all flukes have operculated eggs. The only other operculated 

 (with a lid) eggs we meet with in man are those of the Dibothrioceph- 

 alidae. 



Flukes have two suckers which, except in the Paramphistomidae, 

 are quite near each other one is termed the oral sucker and the 

 other the ventral sucker or acetabulum. The intestinal tract consists 

 of a pharynx, proceeding from the oral sucker, which bifurcates and 

 terminates in blind intestinal caeca. The life history of the important 

 human flukes is unknown. It is supposed that this, in a measure, may 

 resemble that of the common liver-fluke disease of sheep (sheep rot). 

 In this the eggs containing a ciliated embryo (Miracidium) pass out in 

 the faeces. This embryo is hatched out and, gaining the water, swims 

 about actively until it reaches some suitable mollusk or crustacean 

 (Limnaea trunca'tula). By means of a pointed end, it bores its way 

 into the body of the gastropod and becomes either a bag-like structure 

 (the sporocyst) or develops into a creature with an alimentary canal 

 (redia). From the sporocyst or redia minute little worms resembling 

 adult flukes in possessing suckers, but differing in the possession of a 

 tail, develop (Cercaria). Having reached maturity, these cercariae 

 leave the sporocyst or redia, and, as in case of F. hepatica, become 

 encysted on blades of grass, to be eaten by sheep and again com- 

 mence the cycle. The encysted cercariae develop into adult liver 

 flukes. It is probable that with many flukes the cercariae enter some 

 host, as mollusk, insect or fish, and that it is by eating such animals as 

 food that man becomes infected. Looss thinks it possible that the 

 miracidium of Schistosum haematobium may bore its way directly into 

 man, as do the larvae of the hook-worm. Manson also suggests that 

 the reporting by Musgrave of 100 mature lung flukes in a psoas 

 abscess makes it very probable that these parasites entered the body 

 as miracidia. The idea in China is that the infection with the com- 

 mon liver fluke of man is brought about by eating fish. Fluke disease 

 is generally known as distomatosis or distomiasis. 



LIVER FLUKES. 



Fasciola hepatica. This fluke, while of enormous economic 

 importance by reason of destruction of sheep, has only been reported 



