Parasites and Parasitic Diseases of Sheep. 33 
tapeworm by administration of tapeworm treatments four times a 
year. For these treatments, see page 25. 
FLUKES. 
Flukes are usually flat, leaflike animals, provided with suckers, 
but not segmented like the tapeworms. They occur in the adult 
stage in various locations, the stomach, intestines, liver, lungs, blood 
vessels, and may occur in immature stages in such tissues as the 
muscles. The adult flukes produce eggs of microscopic size which 
pass out and hatch in water. The embryos released from the eggs 
infect snails in which they transform into a succession of larval 
stages. The parasites finally escape from the snails and may pene- 
trate the skin of the final host or may be swallowed, sometimes after 
encysting, in food or water. 
Sheep in certain localities in the United 
States, as well as in other parts of the world, 
suffer considerably from fluke infestation. The 
common liver fluke and the large liver fluke oc- 
cur in American sheep. 
THE COMMON LIVER FLUKE.?° 
Fic. 22.—Common liver 
‘ : , fluke (Fasciola he- 
Location——These flukes are found usually in patica). Natural size. 
the biliary canals and the ducts of the liver, ‘(From Stiles, 1898.) 
though they may occur as wandering parasites in the lungs and else- 
where. 
Appearance.—The common liver fluke is a flattened, leaflike, 
brown animal, usually about an inch long (fig. 22). There is a 
sucker at the anterior, or front, end, on a cone-shaped extension, and 
just behind this is a ventral sucker. Through the skin or cuticula 
covering the animal one can see the branching intestine and the 
uterus filled with eggs 
Life history.—The eggs produced by the adult flukes pass out in 
the feces and on getting to water release a ciliated embryo. This 
embryo attacks certain species of snails and on entering the snail 
undergoes certain changes, which in time give rise to a form called 
a cercaria. This is like a small fluke, provided with a tail by means 
of which it swims about. Finally it loses the tail and encysts. The 
encysted cercariz may float about on or in water or may be attached 
to grass blades or other vegetation. When these are swallowed 
by sheep, or other suitable host animals, the larval flukes escape 
in the digestive tract and bore their way through the intestinal 
15 Fasciola h Ponti. 
