IG Experiments on the Development of the Liver-Jlulie. 
armed with fine spines from the first. And lastly, he considers 
it improbable that these cercariaj pass into the ultimate host 
without previously encysting ; for the head-spine is a boring 
apparatus, which in other cercariae is employed in penetrating 
the host in which the encysted stage is passed. But it is pos- 
sible that this boring-spine may be required by the cercaria to 
enable it to leave the inner envelope of the sporocyst, which 
appears to be very tough. 
However, some twenty slugs of the same lot as the Arion in 
question, which had not been exposed to infection with F. hepa- 
tica, had previously been dissected and found free from trematode 
larvae, and the presence of a cercarian form in one of those which 
bad been so exposed was highly suspicious. But fifty-six more 
Arions were obtained from the same source, through the kindness 
of Mr. W. Hatchett-Jackson, and of these two proved to be infested 
with the same Cercaria limacis. They came from a garden at 
Weston-super-mare, surrounded by high walls ; the nearest sheep 
were two miles away, and the nearest rabbits a mile ; so that it 
was highly improbable that slugs would get infected with Fasciola 
hepatica under such circumstances. In order that the question 
might be decided, a rabbit was fed at different times with several 
thousands of these sporocysts, and, after a time, its droppings 
examined for eggs. None were found, and when the rabbit was 
eventually killed, the liver was perfectly free from flukes. 
Attempts were also made to infect different aquatic mollusca. 
Similar experiments have been carried on for particular snails by 
other zoologists, but always without success. Leuckart (I.e. 
p. 765) has experimented upon LimncBUs stacjnalis and pereger, 
Physa fontinalis, Planorbis vortex and carinatus ; von Linstow * 
upon Succinea amphibia and Planorbis vortex. 
I have experimented upon Planorbis marginatus, Snccinea 
amphibia, Limnaius pereger and L. truncatulus. The snails were 
brought together with very large numbers of embryos in a small 
vessel, and the snails subsequently examined. Several forms of 
larval trematodes were found during the experiments, but none 
which could be connected with F. hepatica. Similar experi- 
ments were tried with Gammarus pulex, as an extremely common 
and generally distributed form, although the probability of this 
serving as host appears to be slight. Eggs also containing 
mature embryos were given to Gammarus, and were readily 
devoured by it. Most of the eggs, however, were crushed by 
their jaws, though a few uninjured ones were found in the 
digestive tract. But here also infection failed. 
The failure of infection-experiments in the hands of different 
* ' Archiv fur Naturgescliichte,' 1875, p. 194. 
