Development of the Liver-Fluke. 
443 
with difficulty. At the anterior end the deeper layer of tissue 
contains the two crescentic eye-spots, which are now in contact, 
and are formed by two cells containing dark pigment. About 
the middle of the body on each side is a large tongue-like cilium 
in constant motion within a long funnel-shaped space. Each 
cilium is borne by a nucleated cell. Within the body-wall of 
the embryo is a space occupied in front by a granular mass in 
which no cellular structure can be seen, but which is probably 
a rudimentary digestive tract, and is filled behind with clear 
round nucleated cells — the germinal cells. 
Fig. 2. 
Embryo of Liver-fluke boring into a snail. Magnified 370 diameters. 
The embryos which have entered the snail are, as a rule, 
found in the respiratory chamber, at the furthest point from the 
entrance, and close by the kidney. The embryos might swim 
in at the opening, though the snail is very sensitive to any 
touch in this neighbourhood ; and an object so large compared 
with the size of the snail as the embryo is, would probably, in 
trying to enter, produce sufficient irritation to cause the snail to 
close the opening. I am inclined to think that the embryos 
enter by boring, and this view is supported by the occasional 
presence of an embryo in the body-cavity, or even in the sub- 
stance of the foot. The first change the embryo undergoes 
after entering the snail appears to be the loss of the outer layer 
of flat ciliated cells, the cilia no longer being of any service. 
A thin cuticle is secreted by the body-wall and covers the 
Avhole of the outer surface. Embryos may sometimes be seen 
which have lost the ciliated cells, but still retain the conical 
form. This elongated conical form is, however, very soon lost, 
and the embryos take an elliptical shape, such as is shown in 
Fig. 3, p. 444. The eye-spots of the embryo become detached 
from one another, and lose their crescentic form ; but they, as well 
as the head-papilla, persist, showing the identity of this young 
sporocyst — for such it is — with the embryo of the liver-fluke. 
