at there are many and serious difficulties in
understanding how many of the inhabitants of the more remote islands,
whether still retaining the same specific form or subsequently modified,
have reached their present homes. But the probability of other islands
having once existed as halting-places, of which not a wreck now remains,
must not be overlooked. I will specify one difficult case. Almost all
oceanic islands, even the most isolated and smallest, are inhabited
by land-shells, generally by endemic species, but sometimes by species
found elsewhere striking instances of which have been given by Dr. A.A.
Gould in relation to the Pacific. Now it is notorious that land-shells
are easily killed by sea-water; their eggs, at least such as I have
tried, sink in it and are killed. Yet there must be some unknown,
but occasionally efficient means for their transportal. Would the
just-hatched young sometimes adhere to the feet of birds roosting on
the ground and thus get transported? It occurred to me that land-shells,
when hybernating 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
hybernating, 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 country 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 100 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 is 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