4 Experiments on the Development of the Liver-Jluhe. 
papilla, and these are thicker than the other cuticular cells, 
often forming ear-like projections at the side of the embryo 
and resembling epaulets. Beneath this cuticle the substance 
of the body is made up of delicate vesicular nucleated cells, 
which, whilst the animal is living, have very indistinct out- 
lines. In some embryos the central cells appear to be arranged 
in more or less distinct rounded masses. A little way behind 
the first ring of cells is situated the eye-spot, which belongs to 
the deeper layer of the body. It does not resemble the sign of 
multiplication as has been described, but is really double, and 
is formed by two crescentic masses of dark pigment, placed 
with their convex sides turned towards each other, and in con- 
tact near the anterior horns. Beneath the cuticle, and especially 
just behind the eye-spots, are numerous yellowish, strongly 
refracting fat-granules. Just behind the head-papilla there 
is a globular portion of the body which has a somewhat 
different appearance from the rest of the parenchyma, and reacts 
differently with staining agents. This may possibly be the 
rudiment of a digestive tract, but it is only slightly differen- 
tiated as yet. Narrow passages may be indistinctly seen on 
either side of the embryo ; these are the excretory vessels, which 
have been found in several other trematode embryos. Mid- 
way between the extremities of the body, and on the right and 
left of the middle line, are two funnel-shaped spaces provided 
with cilia in constant motion. 
Under ordinary conditions the head-papilla of the embryo is 
truncated in front, and seems to have a slight depression in 
its centre ; but when the embryo is engaged in boring, the 
depression disappears and the papilla becomes longer, conical, 
and distinctly pointed, and indeed often appears to be terminated 
v/ith a short style. 1 have not been able to demonstrate the 
presence of any chitinous structure, but this pointed papilla 
would undoubtedly prove a very efficient boring-tool. The 
embryo may often be seen attempting to bore its way into the 
glass of the slide under the microscope ; it spins round and 
round on its longitudinal axis, alternately drawing up its body 
and suddenly stretching it out at full length. I have observed 
one boring for more than half-an-hour at its own empty egg- 
shell, which happened to be on the same slide, and only giving up 
the attempt when it was too feeble to move away. 
In water the average duration of the embryo's life is only about 
eight hours, though occasionally one may live over night. The 
motion then becomes gradually feebler, and at length ceases ; 
the embryo assumes an oval or elliptical shape; the ciliated 
cuticular cells absorb water, and swell up into round vesicles, 
and the whole body disintegrates. In mucus the embryo will 
