25 
(c) Free-swimming ciliated miracidium (fig. 23). — As already stated, this organism 
is entirely different from its mother. It measures about 0.15 mm. long. It is some- 
what broader in its anterior portion than in its poste- 
rior j^ortion; on its anterior extremity we find a small 
eminence known as a boring papilla; the exterior sur- 
face of the young worm is covered with numerous cilia, 
which by their motion propel 
the animal through the water; 
inside the body we find in the 
anterior portion a simple ves- 
tigial intestine and a double 
ganglionic mass, provided with 
a peculiar j)igmented double 
cup-shaped eye-spot; in the 
posterior portion of the body 
cavity is found a number of 
germ cells, which develop into 
individuals of the next gen- 
eration. 
Swimming around in the wa- 
ter, the miracidium seeks out 
certain snails {Limnsea irunca- 
tula, L. oahuensis, L. rubella^ see 
p. 38), which it immediately 
attacks (fig. 23 ) . The miracid- 
ium elongates its papilla and fastens itself to the 
feelers, head, foot, or other exterior soft portions of 
the body of the snail; some of the parasites enter the pallial 
(lung) cavity and attach themselves there. After becoming 
securely fastened to the snail the miracid- 
ium discards its ciliated covering and 
shortens to about half its former length 
(0.07 mm. to 0.08 mm.). The parasites 
now bore their way into the body of the 
snail and come to rest in the liver, or near 
the roof of the pallial cavity, etc., the 
movements gradually cease, and we have 
before us the stage known as the — 
{d) Sporocyst (figs. 24 and 25). — The 
eye-spots, ganglionic swellings, and ves- 
tigial intestine become more and more 
indistinct and are finally lost. The spo- 
rocyst grows slowly at first, then more 
rapidly, and at the end of 14 days or so 
measures 0.5 mm. The germ cells men- 
tioned as existing in the posterior portion 
of the miracidium now develop into indi- 
viduals of the third generation known 
Fig. 23.— Embryo of the Common 
Liver Fluke {Fas^ciola hcpatica) 
boring into a snail, x 370. (Af- 
ter Thomas, 1883, p. 285, fig. 4.) 
Fig. 24. — Sporocyst of the 
Common Liver Fluke 
which has developed 
from the embryo, and 
contains germinal cells. 
X 200. (After Leuckart, 
1889, p. 109, fig. 67 B.) 
Fig.. 25. — Sporocyst of 
the Common Liver 
Fluke, somewhat old- 
er than that of fig. 24, 
in which the germi- 
nal cells are giving 
rise to redise. x 200. 
(After Leuckart, 1889, 
p. 109, fig. 67 C.) 
as- 
{e) Redise (figs. 26 and 27). — The redise 
escape from the sporocyst when the latter 
is from 2 weeks (in summer) to 4 weeks 
(in late fall) old. Upon' leaving the body of the sporocyst they wander to the liver 
of the snail, where they grow to about 2 mrn. long by 0.25 mm. broad. Each redia 
Fig. 26. — Redia of the 
Common Liver Fluke 
{Fasciola hepatica)i 
containing germinal 
cells which are devel- 
oping into cercarise. 
X 150. (After Leuck- 
art, 1889, p. 269, fig. 
129 A.) 
