a field as one of the most
recent of continental islands. Looking at the general bearing of these
facts, they prove, that the idea so generally entertained as to the
biological identity of the British Isles with the adjacent continent is not
altogether correct. Among birds we have undoubted peculiarities in at least
three instances; peculiar fishes are much more numerous, and in this case
the fact that the Irish species {371} are almost all different from the
British, and those of the Orkneys distinct from those of Scotland, renders
it almost certain that the great majority of the fifteen peculiar British
fishes are really peculiar and will never be found on the European
Continent. The mosses and Hepaticae also have been sufficiently collected
in Europe to render it pretty certain that the more remarkable of the
peculiar British forms are not found there; why therefore, it may be well
asked, should there not be a proportionate number of peculiar British
insects? It is true that numerous species have been first discovered in
Britain, and, subsequently, on the continent; but we have many species
which have been known for twenty, thirty, or forty years, some of which are
not rare with us, and yet have never been found on the continent. We have
also the curious fact of our outlying islands, such as the Shetland Isles,
the Isle of Man, and the little Lundy Island, possessing each some peculiar
forms which, _certainly_, do not exist on our principal island which has
been so very thoroughly worked. Analogy, therefore, would lead us to
conclude that many other species or varieties would exist on our islands
and not on the continent; and when we find that a very large number (150)
in three orders only, are so recorded, we may I think be sure that some
considerable portion of these (though how many we cannot say) are really
endemic British species.

The general laws of distribution also lead us to expect such phenomena.
Very rare and very local species are such as are becoming extinct; and it
is among insects, which are so excessively varied and abundant, which
present so many isolated forms, and which, even on continents, afford
numerous examples of very rare species confined to restricted areas, that
we should have the best chance of meeting with every degree of rarity down
to the point of almost complete extinction. But we know that in all parts
of the world islands are the refuge of species or groups which have become
extinct