23 
I 
This worm is ^ | 
! yeiy common in = p 
, Europe and not | ^ 
uncommon in the ^ 
: United States. 
From an agricul- 5 | 
I tural standpoint it | 
is the most impor- ^ | 
taut of the flukes, ^ % 
but from a stand- 
point of human '*2. 
medicine it is much ^ ? 
less important ? | 
than several other 
forms, notably "g 5 
Pa r a g 0 n i m u 6 - , = | 
Ojjlsthorchis^ and | 
Schistosoma. | | 
Life history. — 1 1 
As an example of ^ s 
the life histoiy of 1 1 
flukes, we may take f: 5 
that of Fasciola | 
h e p a t i ca^ which | | 
may be summa- ? 
rized as follows: ^ 
< K 
{a) The adult henna- 6. § 
phrodtiic v'orm (figs. ?. p 
19-20), the characters E 
of which are given on ^ 5 
p. 22, fertilizes itself = 
or a cross fertilization ~ 
of two individuals g Y 
takes jdace in the bili- p ^ 
ary passages of the o 2 
liver, and produces a ^ 
large number ( esti- E C. 
mated at 37,000 to g 
45,000) of eggs. ^ 
{h) Eggs (tigs. 21 ||- 
and 22). — Each egg is E 3 
composed of the fol- ^ '2 
lowing parts: (1) A s- 
true germ cell, which | 
originates in the ovary S 2 
and is destined to give H 
rise to the future em- £ g 
bryo; (2) a number of f ^ 
vitelline or yolk cells, g 5 
which are formed in a 5 
