( 439 ) 
XXIII. — SecoHd Report of Experiments on the Development of 
the Livcr-Fluke (Fasciola hepatica). By A. P. Thomas, 
M.A., F.L.S., Balliol College, Oxford. 
My experiments on the development of the liver-fluke were 
continued during the summer and autumn of last year, and 
other experiments have been performed during the present 
year, or are still in progress. 
Renewed search was made for the intermediate host of the 
liver-fluke, and I again endeavoured to infect molluscs with 
the embryo. These experiments have been almost entirely 
confined to fresh-water snails. From the consideration of the 
geographical distribution of the liver-fluke, and of the various 
species of mollusca, I was led to strongly suspect Limjiceus 
pereger of being the host of the long-sought larval form. The 
only two fresh-water snails found in the Faroe Islands, where the 
liver-fluke is very common, according to von Willemoes-Suhm,* 
are Limnaus pereger and L. truncatulus. The only aquatic pul- 
monate in the Shetland Islands t where the fluke also occurs 
is Limnceus pereger. If then the bearer of the larval form of 
Fasciola hepatica is a fresh-water snail, there is a strong case 
made out against Limnceus pereger. 
But the question naturally presented itself whether more 
than one species of mollusc might not be able to act as carrier 
of the larval form. During previous investigations I had come 
across numerous forms of cercariae, and many of these occurred 
in two or more species of molluscs, these again being frequently 
not the same species as those in which other observers had 
found the same cercariae. I believe that the larval forms of 
trematodes are not so closely restricted to certain intermediate 
hosts as was formerly supposed, but that they may occur in any 
species which do not differ too widely either in the nature of 
their tissues or their habits of life. Some species will, how- 
ever, be more sensitive than others to such differences. 
It was therefore considered desirable to repeat infection- 
experiments on a number of our common water-snails. The 
common occurrence of the liver-fluke is perhaps partly due to 
several species of snails being able to serve as intermediate 
hosts. Limnceus truncatulus, in particular, I was inclined to 
suspect, as it was almost the only species of water-snail 
occurring on the clearly circumscribed area of infection at 
Wytham, mentioned in my former paper,J my suspicions being 
* ' Zeitschrift fur ■wissenscliaftliche Zoologie,' vol. xsiii., p. 339. 
t Forbes, British Association Eeports, 1859, p. 127. 
+ First Eeport of Experiments. This Journal, vol. xvii. 18S1, p. 19. 
