Experiments on the Development of the Liver-fluke. 
15 
parent cuticle, covered with fine "granules ; and beneath this 
is a layer of circular and longitudinal muscular fibres, most 
strongly marked in the neck, and then a layer of delicate 
rounded cells, between which are numerous fine calcareous 
granules, which give the sporocysts a yellowish colour by trans- 
mitted, and a milky appearance by reflected light. But the 
most striking peculiarity of this sporocyst is the presence of an 
inner sac, formed by a transparent structureless membrane. This 
sac lies loosely within the outer cellular one, and, in those sporo- 
cysts which were seen to move, slipped to and fro within the 
outer contractile walls. It contains usually nine or ten cercariae, 
swimming in a transparent liquid ; the cercaria is provided with 
a boring-spine imbedded in the wall of the oral sucker, and has 
a very rudimentary stump-like tail. The sporocysts multiply 
by transverse division. 
These sporocysts are not provided with any boring organ 
except the neck, which has been described, and the tissues of 
this must be very soft, but they are, nevertheless, able to pene- 
trate the thick integument of the slug. They were observed 
with the aid of the microscope emerging from the whole of the 
fore-part of the dorsal surface of the Avion. First a slight 
tremulous motion was noticed, then a drop of milky perspira- 
tion seemed to gather upon the black surface. This was the 
sporocyst itself, but no very distinct movement could be noticed 
in it. The end carrying the neck emerged first, and, when the 
whole was well out of the slug's body, it fell over on one side, and 
lay perfectly inert and motionless. The sporocysts seemed to 
be aided in making their way out of the tissues of the host by 
the slug itself, for when this was irritated, and so caused to shed 
out a larger quantity of mucus, the sporocysts appeared rapidly 
and in large numbers. Over two thousand were given out by a 
single slug in forty-eight hours. They are left behind in the 
mucous trail of the slug, and in any moist locality the included 
cercariae remain alive for a day or two. As they are thus scat- 
tered over the gronnd wherever the host crawls, they may be 
easily swallowed by any herbivorous animal whilst feeding. 
Such a mode of distribution would be highly favourable to the 
cercaria of Fasciola hepatica. 
Leuckart, in his well-known work on ' Parasites,' has ob- 
jected * to Moulinie's conjecture, on account of the presence 
in this Cercaria limacis of a head-spine and the associated 
so-called " salivary glands," which in all probability are wanting 
in the cercaria of the liver-fluke. The outer surface also is 
smooth, whereas Fasciola hepatica probably possesses a cuticle 
* ' Die menscliliclien Parasiten,' vol. i. pp. 521 and 570. 
