FARM PESTS SI 



hajjpily for the sheep, not only 100 to 1 but 10,000 chances 

 to 1 against the Hverfiuke egg reaching maturity, but where 

 these sheep droppings are on wet pasture some eggs are 

 bound to get washed down to lower levels where there are 

 streams. Then, after hatching into a swimming embryo 

 it searches out one particular kind of water-snail, Limnax 

 iruncatula, and bores its way into its body, whereupon 

 the snail suffers from liverfluke, and these embryos produce 

 organisms similar to the adult parasite, with a mobile 

 tail. At this stage they leave the body of the snail and 

 crawl up and attach themselves to a blade of grass near 

 the water's edge, losing their tail then and remaining 

 quiescent until swallowed by some unlucky sheep which 

 comes down to drink. Once arrived at the height of its 

 ambition inside the sheep's liver, the fluke commences in 

 real earnest and sets up irritation and a distending of 

 the biliary ducts, with dire results. Although the sheep 

 does not appear to be affected much at first, and may 

 indeed for a short time even put on flesh, the final stage 

 is loss of appetite, debilitation and death. Sometimes 

 they get over it, on the eventual departure of the fluke 

 organism, but they are never the same again. 



Remedial measures consist in keeping sheep as much as 

 possible on dry uplands. It should always be remembered 

 that the sheep as a domestic animal has been obtained by 

 selective breeds from a wild type, like a goat, whose 

 natural place was among the sparse dry herbage on the 

 tops of the mountains. Sheep will be generally better 

 if reared under conditions that more nearly approach the 

 natural environment than on low-lying ground, which 

 tends to produce foot-rot in addition, although we have 

 a strain, the Romney Marsh breed, which would seem to 

 have become inured to conditions on soft ground. 



I should have mentioned in the case of the acarus tick 

 that the habit of this creature of falling off for moulting 

 and egg-laying purposes to retm-n to sucking on some other 

 animal brings in another complication, viz. the transmit- 



