PARASITOLOGY. 163 
state. It loses its layer of ciliated epithelial ceils and 
the small mass of round cells forming the interior of 
the body rapidly grow; it soon develops into the Spo- 
rocyst. From the cells inthe sporocyst are formed 
five to eight redia; each redia in turn develops 
from fifteen to twenty cercaria; the cercaria is the 
fully developed larval stage, oval in shape, provided 
with an oral and ventral sucker, a rudimentary di- 
gestive tract and a tail. It now leaves the snail and 
is enabled to move about in the water by means of 
its tail and crawls upon a blade of grass or an 
aquatic plant; it loses its tail at this period and be- 
comes encysted with a gelatinous substance with 
which it provides itself; this is the fully developed 
larval stage. The cysts are the most numerous on 
the part of the grass close to the ground; the larva 
retains its vitality for a long time if it isin a moist 
locality; these cysts appear as very small white 
specks and are eaten by the herbivora grazing upon 
these infested pastures. The cyst upon reaching the 
stomach is digested and the larva, set free, soon tinds 
its way to the bile duct, and thence to the liver. 
Animals Intested.—The ox, sheep, goat, pig, horse, 
and man. 
Part Intested.—The liver. 
Conditions Produced.—The worms invade the bile 
ducts and here develop into the mature worm; here 
they live for six months, then die. In autopsy work 
one’s attention is attracted by the enlargement of 
the large bile duct on the posterior face of the 
liver; a cut section of this part shows a greatly 
thickened wall and many worms contained within 
the duct; the bile may be somewhat thicker than 
