Tond-snaih 3 1 5 



winter of 1879-80 ; but wo may briefly explain tliat 

 millions of the eggs of this pest are voided with 

 the excrement of diseased sheep. If such an animal 

 is turned out on a marshy pasture there will probably 

 be an abundance of L. triincatula among the grass. 

 If not, all those eggs will be wasted. They will 

 hatch, it is true, regardless of the presence or absence 

 of snail-life, but unless the embryos meet with this 

 Limncea within eight hours after hatching, they 

 perish. No other snail — not even another species of 

 Limncea — will serve their purpose, but if truncatula 

 be there the first step in the destruction of a flock of 

 sheep may be said to have been taken. The Distoma 

 that is to fulfil its mission enters the branchial 

 chamber of the mollusk, and there attains a stage 

 of development that fits it for a different life. 

 About midsummer, when the grass has all dis- 

 appeared from the uplands, the sheep are turned 

 into the marshy bottoms where there is still green 

 feed. About the roots of the grass there are also 

 many truncatidas with their branchial chambers 

 well furnished with Flukes. Sheep are fond of 

 snails; and this would appear to be a fact well 

 considered in the Distonias plan of campaign. 

 Snails and grass are eaten, and the Flukes, proof 

 against the action of the digestive fluids, find their 

 way to the sheep's liver, and begin to set up that 

 condition of things which the farmer knows as 

 " Rot." Other species of Distoma that cause similar 

 trouble to vertebrates, spend their earlier stages in 

 the bodies of snails. Thus, D. eiidolahiim selects 

 L. stagnalis as a wet-nurse, and may pass its second 

 stage in the same species, or may change over to 



