n
South America by inundations, bearing on them the tiger, cayman,
squirrels, and other quadrupeds.

But though actual observations of such abnormal instances of the
dispersal of animals are few, many experiments have been made to
demonstrate the possibility of a passive transportal of species over
wide distances. It was especially Darwin who gave a great stimulus by
setting the example to those interested in natural history in the
conduct of such researches. He was struck by the fact that, though
land-shells and their eggs are easily killed by sea-water, almost all
oceanic islands, even the smallest and most isolated, are inhabited by
them, and felt that there must be some unknown but occasionally
efficient means for their transportal (p. 353). To quote his words: "It
occurred to me that land-shells, when hibernating and having a
membranous diaphragm over the mouth of the shell, might be floated in
chinks of drifted timber across moderately wide arms of the sea. And I
find that several species in this state withstand uninjured an immersion
in sea-water during seven days: one shell, the _Helix pomatia_, after
having been thus treated and again hibernating, was put into sea-water
for twenty days, and perfectly recovered. During this length of time the
shell might have been carried by a marine current of average swiftness
to a distance of 660 geographical miles. As this _Helix_ has a thick
calcareous operculum, I removed it, and when it had formed a new
membranous one, I again immersed it for fourteen days in sea-water, and
again it recovered and crawled away. Baron Aucapitaine has since tried
similar experiments: he placed one hundred land-shells, belonging to ten
species, in a box pierced with holes, and immersed it for a fortnight
in the sea. Out of the hundred shells, twenty-seven recovered. The
presence of an operculum seems to have been of importance, as out of
twelve specimens of _Cyclostoma elegans_ which it thus furnished, eleven
revived. It is remarkable, seeing how well the _Helix pomatia_ resisted
with me the salt-water, that not one of fifty-four specimens belonging
to four other species of _Helix_ tried by Aucapitaine, recovered. It is,
however, not at all probable that land-shells have often been thus
transported; the feet of birds offer a more probable method."

We have here positive evidence that such shells as _Helix pomatia_ and
_Cyclostoma elegans_ might easily be transported to an island from the
ma