e its kind."

All zoologists, indeed, are quite in accord with Dr. Wallace's view as
expressed in _Island Life_ (p. 74). "Whenever we find that a
considerable number of the mammals of two countries exhibit distinct
marks of relationship, we may be sure that an actual land-connection, or
at all events an approach to within a very few miles of each other, has
at one time existed." As all the European islands come under this
category, their mammals exhibiting distinct relationship with those on
the European continent, they all have been connected with it formerly.

Perhaps the most powerful of all agents in the transportal of species by
accidental means is man. But his actions may be accidental as well as
intentional. We have therefore to distinguish between the animals
disseminated all over the world by pure chance, and those which have
been introduced into new countries purposely. Invertebrates, such as
snails, centipedes, woodlice, beetles, and cockroaches, are constantly
being unintentionally carried with vegetables, fruit, trees, and with
timber from one country to another. Earthworms are sometimes transported
in the balls of earth in which the roots of trees are enveloped. As
regards molluscs, Mr. Kew believes (p. 178) that during the last three
centuries at least, human agency has influenced their disposal more than
all other causes taken together. A large number of species of
invertebrates in America are said to owe their existence in that country
to accidental introduction by man. In most cases, however, no
particular reason can be assigned why they should have been thus
introduced, and as a matter of fact there are always individual
differences of opinion as to the precise number of such. Certain it is,
that though the number of supposed introductions from Europe to America
is very large, those which have been carried from America to Europe is
exceedingly small. In fact, I remember only two instances of accidental
animal importations from America which have firmly established
themselves in Europe, viz., a small fresh-water mollusc, _Planorbis
dilatatus_, and the much-dreaded vine-pest, _Phylloxera vastatrix_.

As a rule the animals die out very shortly after their arrival on
foreign soil. Many instances, nevertheless, are on record, especially in
the case of molluscs, where snails thus transported have not only
survived but are apparently in a flourishing condition and spreading.
_Helix aspersa_, for example, o