ions of certain
orders of plants,--herbaceous forms having been developed into trees,
etc.,--seem to me to accord better with the view of occasional means of
transport having been largely efficient in the long course of time, than
with the view of all our oceanic islands having been formerly connected
by continuous land with the nearest continent; for on this latter
view the migration would probably have been more complete; and if
modification be admitted, all the forms of life would have been more
equally modified, in accordance with the paramount importance of the
relation of organism to organism.

I do not deny that there are many and grave difficulties in
understanding how several of the inhabitants of the more remote islands,
whether still retaining the same specific form or modified since their
arrival, could have reached their present homes. But the probability of
many islands having existed as halting-places, of which not a wreck now
remains, must not be overlooked. I will here give a single instance of
one of the cases of difficulty. 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. Dr. Aug. A.
Gould has given several interesting cases in regard to the land-shells
of the islands of the Pacific. Now it is notorious that land-shells are
very easily killed by salt; their eggs, at least such as I have tried,
sink in sea-water and are killed by it. Yet there must be, on my view,
some unknown, but highly efficient means for their transportal. Would
the just-hatched young occasionally crawl on and 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 found that several
species did in this state withstand uninjured an immersion in sea-water
during seven days: one of these shells was the Helix pomatia, and after
it had again hybernated I put it in sea-water for twenty days, and it
perfectly recovered. As this species has a thick calcareous operculum,
I removed it, and when it had formed a new membranous one, I immersed it
for fourteen days in sea-water, and it recovered and crawled away:
but more experiments are wanted on this head. The most striking and
important fact for us in