Development of the Liver-Fluhe. 
441 
of a path near the ditch, and these seem to have crawled out of 
the grass when revived by the rain. At the roots of the grass, 
along the margin of the ditch, others were found in abundance. 
Some few shells were quite empty, but the majority contained 
the dried remains of the snail, which had shrunk far back into 
the spire of the shell. Most of these appeared to be quite dead, 
but were however merely dormant, for on placing them in water 
the tissues imbibed moisture and assumed their normal bulk, and 
after a few hours the snails had regained their full activity, and 
were seemingly none the worse for their prolonged desiccation. 
To give an idea of their abundance, Mr. Hatchett-Jackson 
and I collected from a comparatively small strip of ground at 
the side of the ditch mentioned, and within two hours, over 400 
examples, and of these more than 300 are now living in my 
aquaria. When these snails are kept in an aquarium, 
they habitually crawl out of the water, and if not constantly 
put back will dry up on the sides of the vessel. Indeed, 
it may be well to note here that L. truncatulus requires 
special precautions to keep it healthy and active in confinement. 
It is clear to me from experience gained in this investigation 
that the species of snail under consideration, when left on the 
fields by the passing away of a flood, continues to wander and 
feed so long as the bottom of the grass remains moist. It is 
equally clear that the numbers so left are recruited from sur- 
rounding ditches and streams. A drought may render the snail 
dormant, but, unless too long continued, it revives at the first 
shower of rain. If there are fluke-eggs on the ground, and the 
season is wet enough for these to develop, the L. truncatulus 
will most certainly be infected with the larval forms of the 
liver-fluke, for, as Avill be seen further on, I have been able to 
prove that Limnaus truncatulus is the principal intermediate 
host of this destructive parasite. 
The snails upon which my infection-experiments were tried 
last summer, were Limnceus pereger, L. auricularis, L. palustris, 
Planorhis niarginatus, P. carinatus, P. vortex, P. spirorbis, Physa 
fontinalis, and Bithynia tentaculata. I was here to a great ex- 
tent going over experiments already tried, at least for some of 
the species, by various workers as well as by myself during the 
previous summer, but always without success. As the cause 
of this want of success might lie partly in the abnormal con- 
ditions of snail-life in the laboratory, the experiments were 
performed in large aquaria, and much trouble was taken to 
secure favourable conditions of temperature, abundant food, <Scc., 
for the inhabitants. But though I obtained evidence that the 
embryos of the flukes do enter the snails, I was unsuccessful in 
obtaining any further development. 
