thers less able to adapt themselves to different
conditions have survived only in one or two lakes in a single district; or
these last may have been originally identical with other forms, but have
become modified by the particular conditions of the lake in which they have
found themselves isolated.
_Peculiar British Insects._--We now come to the class of insects, and here
we have much more difficulty in determining what are the actual facts,
because new species are still being yearly discovered and considerable
portions of Europe are but imperfectly explored. It often happens that an
insect is discovered in our islands, and for some {345} years Britain is
its only recorded locality; but at length it is found on some part of the
continent, and not unfrequently has been all the time known there, but
disguised by another name, or by being classed as a variety of some other
species. This has occurred so often that our best entomologists have come
to take it for granted that _all_ our supposed peculiar British species are
really natives of the continent and will one day be found there; and owing
to this feeling little trouble has been taken to bring together the names
of such as from time to time remain known from this country only. The view
of the probable identity of our entire insect-fauna with that of the
continent has been held by such well-known authorities as the late Mr.
E. C. Rye and Dr. D. Sharp for the beetles, and by Mr. H. T. Stainton for
butterflies and moths; but as we have already seen that among two orders of
vertebrates--birds and fishes--there are undoubtedly peculiar British
species, it seems to me that all the probabilities are in favour of there
being a much larger number of peculiar species of insects. In every other
island where some of the vertebrates are peculiar--as in the Azores, the
Canaries, the Andaman Islands, and Ceylon--the insects show an equal if not
a higher proportion of speciality, and there seems no reason whatever why
the same law should not apply to us. Our climate is undoubtedly very
distinct from that of any part of the continent, and in Scotland, Ireland,
and Wales we possess extensive tracts of wild mountainous country where a
moist uniform climate, an alpine or northern vegetation, and a considerable
amount of isolation, offer all the conditions requisite for the
preservation of some species which may have become extinct elsewhere, and
for the slight modification of others since
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