PARASITES OF ANIMALS. : 105 
their tails, but eventually they, in all probability, again enter 
the bodies of other small snails, and losing their tails, become 
encysted in little capsules. Finally these snails, with their 
parasites, are swallowed by sheep and cattle, while adhering 
to the herbage growing on moist land or near the water, 
or when adhering to water-cresses they might be swallowed 
by mankind. In the stomach and intestine of these higher 
animals they are again liberated from their cysts. They then 
gain access 49 the liver, where they rapidly develop their 
sexual organs and become mature. Eventually, after they 
have matured and perhaps discharged a large part of their 
eggs, they themselves, or at least a part of them, enter the 
intestine and are discharged, while still living, in company 
with innumerable eggs. The eggs that they still contain may 
be laid after they reach the earth or water. These eggs are 
exceedingly minute and may be diffused in various ways, as 
by rains, winds, insects, and the feet of animals, and getting 
into water, or moist situations, they are ready .o hatch and 
commence another series of transformations. 
The history of most of the flukes, which have hitherto been 
fully investigated, agrees in the main with that above given, 
and there can be little doubt but that this will prove to be the 
case with the common fluke, when its full history shall have 
been ascertained. At any rate it is certain that the eges can 
hatch only in water, or in moist places. Therefore it is evi- 
dent that sheep and cattle will be much more liable to the 
disease when kept in low wet pastures, than in dryer and 
more elevated situations ; and also that wet seasons will be 
favorable for the parasites and dry ones unfavorable. These 
conclusions have been fully sustained by the experience of 
sheep-owners in all countries. 
Modes of Occurrence. 
The liver-fluke is one of the few internal parasites that is 
capable of living in several very different animals. It is most 
common in sheep; less so in cattle, goats, horses, and the 
ass; and quite rare in man. It has also been found in the 
hog, elephant, camel, beaver, squirrels, rabbit, hare, deer, 
and antelopes of sevéieilkinils/end ia the great kangaroo. 
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