inland. The former occurs in France, Holland, and England, and the
latter all along western continental Europe and England. And yet neither
of these species inhabits the Canary Islands, Madeira, or Ireland, none
of which are at too great a distance from Europe to be within easy reach
for a floating object. The fact that _Cyclostoma elegans_ does not live
in Ireland is of particular interest in connection with the
floating-theory just quoted, as on all sides of Ireland dead specimens
have been picked up on the shore, showing that marine currents carry
specimens and have thus transported them for countless centuries.
Nevertheless the species has not established itself in Ireland. If such
a fate meets a land-shell of the type of _Cyclostoma elegans_, it may be
asked, with some justification, what chance slugs or the smaller
non-operculated species would have to reach an island like Ireland
alive from the mainland, and to colonise it successfully.

Both slugs and their eggs are killed by a short immersion in sea-water,
as I have proved experimentally. I have also subjected slugs, in the act
of crawling on twigs, to an artificial spray of sea-water. This seemed
to irritate their tender skins to such an extent that they curled
themselves up, released their hold on the twig and let themselves drop
to the ground. If we supposed, therefore, that a slug had successfully
reached the sea, transported on a tree-trunk, the moisture would tend to
lure it forth from its hiding-place under the bark, whilst the mere
spray would prove fatal to its existence. Those species of snails and
slugs which lead an underground existence, rarely venturing above
ground, such as _Testacella_ and _Coecilianella_, would have even less
chance of being accidentally carried to some distant island.

The suggestion advanced by Darwin (p. 353), that young snails just
hatched might sometimes adhere to the feet of birds roosting on the
ground and thus be transported, appears to me so extremely improbable as
to be scarcely worth serious consideration. Indeed, as Darwin himself
acknowledged later on, it does not help us very much to suggest possible
modes of transport. What we require is direct evidence. How far we are,
however, from obtaining it, may be inferred from Mr. Kew's remark (p.
119), that "we have little or no actual evidence of precise modes of
dispersal even for short distances on land."

A very curious statement was made by a well-known French conc