FLUKES AS PARASITES 201 
minute three-suckered fluke (Udonella cahigorum), numbers of 
which attach themselves to the egg-bags of a degenerate crus- 
tacean (Calzgus), living as a parasite upon the gills of the hake. 
Aquatic Amphibians do not escape from the attacks of Flukes, 
a notable instance being afforded by one of these creatures (Poly- 
stomum integerrimum) which lives, when adult, in the urinary 
bladder of the frog, and illustrates the transition from external 
to internal parasitism. It adheres to the lining 
of the bladder by means of a rounded projec- 
tion at its hinder end, on which are situated six 
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suckers and many small hooks. The numerous 3 A 
eggs are laid in spring, and pass from the frog’s EATS 
body to the exterior, where they hatch out into ~ 3 
minute ciliated larva, which actively swim about RI & 
in search of tadpoles. To understand what ‘s 4 
happens next, it must be remembered that at 
a certain stage in development a fold grows 
back from the head of a tadpole, covering the 
gill-slits, and uniting with the adjacent skin so 
as to enclose a gill-chamber opening to the 
exterior by a small hole or spiracle on the left 
side. The continued existence of the fluke- 
larva depends upon its finding a tadpole within 
twenty-four hours, preferably one in the stage 
described. If successful in this quest it swims 
into the gill-chamber through the spiracle, and 
becomes parasitic upon the gills. After living 5, 1.45 -pight-suckered 
for two months or so in these comfortable See ie Cees 
quarters a change of residence becomes neces- 
sary, for the tadpole is becoming a frog, the gills are disappearing, 
and the gill-slits are closing up. The larva now makes its way 
into the pharynx of its host, and passing through gullet, stomach, 
and intestines, reaches and enters the bladder, where it becomes 
adult in about three years. 
Mention must here be made of a singular species of many- 
suckered Fluke (Dziplozoin paradoxum, fig. 1150) which lays its 
eggs upon the gills of the minnow. Minute ciliated larve hatch 
out, which perish in from five to six hours unless they find another 
host of the same kind. In that case, after further growth, they 
fuse together in pairs, and become X-shaped adults, capable of 
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