Experiments on the Development of the Liver-fiuke. 7 
the contents of the paunch of a recently infected lamb, I found 
numerous portions of the roots of grasses. This view has much 
to recommend it, and in accordance with it is the opinion of 
farmers, that the fluke is especially taken up when the sheep 
graze closely, and that the better the biter is, the worse are the 
chances of escape. We know one form of cercaria inhabiting 
the common black slug, which is left behind in the mucous trail 
of this animal ; but this will be discussed more fully below. 
The following letter has been sent to Professor Rolleston, 
with the request that it may be published. 
" Dr. Gwyn Jeffreys, F.R.S., who has long studied snails and 
slugs, is of opinion that sheep do not willingly or knowingly eat 
them, and that the germs or embryos of the fluke are not intro- 
duced in that way into the sheep's liver. He believes that this 
parasite finds its way into the sheep's body through the feet, or 
the wool when the sheep lies down. He therefore recommends 
that where the sheep are kept on marshy or moist pastures they 
ought to be taken in at night, and for the early part of the 
morning, when the flukes and their nurses (certain snails and 
slugs) are most numerous and active. Upland and dry meadows, 
however, appear to suit sheep better than marshy or moist 
pastures." 
Experiments have been made to determine which mollusc or 
molluscs act as host to the conjectured sporosac form oi Fasciola 
hepatica ; and here the number of molluscs which need concern 
us was indicated by their geographical distribution and by that 
of the fluke itself. As the fluke is only met with on wet 
ground, we may neglect such snails as are confined to high and 
dry ground. Willemoes-Suhm had pointed out * that in the 
Faroe Islands, where sheep suffer severely from the fluke, the 
molluscs are restricted to eight species, viz., Arion ater, 
A. cinctus, Limax agrestis, L. rnarginatus, Vitrina pellucida, 
Hyalina alliaria, Limnceus pereger, and L. truncatulus. Of these, 
Limax agrestis, our common grey slug, was by far the com- 
monest and most injurious, and he suggested that this slug 
might act as intermediate host. In a letter to the ' Times,' of 
April 14, 1880, Professor Rolleston gave reasons for suspecting 
the black slug, Arion ater. He has recently ascertained that the 
liver-fluke does actually occur in the Shetland Islands, where 
the pulmonate molluscs are, according to Forbes,t restricted to 
the five species, Arion ater, Limax cinereus, Vitrina pellucida, 
Helix alliaria, and Limnoius pereger. The only one of these 
which is at all plentiful is Arion ater. Slugs have been received 
from the Shetland Islands as specimens of the only two kinds 
* ' Zeitschrift fur wissenschaftliche Zoologie,' 1873, vol. xsiii. p. 339. 
t ' British Association Eeport,' 1859, p. 127. 
