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 feet of birds offer a more probable method.
ON THE RELATIONS OF THE INHABITANTS OF ISLANDS TO THOSE OF THE NEAREST
MAINLAND.
The most striking and important fact for us is the affinity of the species
which inhabit islands to those of the nearest mainland, without being
actually the same. Numerous instances could be given. The Galapagos
Archipelago, situated under the equator, lies at a distance of between 500
and 600 miles from the shores of South America.
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