102 VETERINARY PARASITOLOGY 
present as in the adult, and there is a simple alimentary 
tract. The Cercaria passes out of the Redia, and after 
a short period leaves the snail and swims about in 
moisture. It next attaches itself to a blade of grass or 
some other object, loses its tail, and secretes a covering 
round itself, thus becoming encysted. It is swallowed 
by an animal, and providing that this be one suitable 
for its further development, it loses its leathery coat, 
passes up the bile-ducts (or, according to some authori- 
ties, the portal veins), and reaches the liver, where it 
becomes adult. 
Occasionally they may reach the lungs, where they 
form cysts containing flukes floating in a brownish fluid. 
Other parts of the body may be similarly invaded. 
Occurrence and Symptoms.—Fluke disease occurs in 
sheep and cattle kept on marshes or in damp surround- 
ings suitable for the development of the snail which acts 
as intermediate host. The embryos reach the liver 
during the last few months of the year, and at first 
cause few or no symptoms. The appetite remains un- 
changed, but there may be a little falling off in condi- 
tion and slight dulness. In other cases death may occur 
from hepatitis, or from embryos, carried by the blood- 
stream, being deposited in organs such as the heart or 
brain. After a few weeks the sheep again regain condi- 
tion, and for a short while appear to be putting on 
flesh. In many parts of the country it is the practice 
to run the sheep on fluky ground in order to fatten 
them more quickly for the butcher. This flesh-forming 
period is only of short duration, and the symptoms now 
become more marked. The wool becomes dry and 
loose in parts, emaciation sets in, and the appetite is 
capricious, while great thirst is a constant feature. 
Ascites, with cedema of the dewlap and’submaxillary 
space, now appears, and the affected sheep show 
dyspnoea and inability to travel fast. The subcu- 
