ur large garden snail, has been
naturalised in many foreign countries by French and Portuguese sailors,
who had taken them on board their ships as food.

It certainly cannot be denied that a number of species among almost all
groups of invertebrates have been unintentionally conveyed by man from
Europe into foreign countries. It has been proposed by Dr. von Ihering
to apply the term "cenocosmic" to those species which have become spread
all over the world through artificial means, and thus to distinguish
them from cosmopolitan ones which have attained a similar range
naturally. The latter he calls "palincosmic" species (_a_, p. 422). Many
so-called cenocosmic ants are believed by Dr. von Ihering to be
palincosmic. We are altogether too apt to regard cosmopolitan as
synonymous with introduced, and we should hesitate before concluding
that because one of our common European species occurs in Australia or
South America, it must have been transported there recently by human
agency. Some of our widely-distributed forms are probably of very great
antiquity, and may have spread to distant lands in early Tertiary times,
when a different state of the geographical conditions enabled them to do
so.

I cannot quote a more appropriate instance than the molluscan fauna of
Madeira. No less than thirteen of the Madeiran snails are looked upon as
having been introduced from Europe by human agency, on the sole evidence
that these happen to be common European species. Yet the correctness of
this supposition must be questioned in face of the interesting
observation made by Darwin (p. 357), "that Madeira and the adjoining
islet of Porto Santo possess many distinct but representative species of
land-shells, some of which live in crevices of stone; and although large
quantities of stone are annually transported from Porto Santo to
Madeira, yet this latter island has not become colonised by the Porto
Santo species. Nevertheless, both islands have been colonised by
European land-shells, which no doubt had some advantage over the
indigenous species." Darwin, therefore, meets the evident anomaly by
suggesting that the European species are supposed to possess some
advantages as colonisers. But the true explanation appears to me to lie
in the supposition that the European land-shells found in the Madeiran
Islands are all, or for the greater part, ancient forms which survived
both there and on the continent, whilst the remainder of the forms
inhab