ormation, and
the presence here of peculiar insects can only be due to isolation with
special conditions, and immunity from enemies or competing forms. When we
consider the similar islands off {355} the coast of Scotland and Ireland,
with the Isle of Man and the Scilly Islands, none of which have been yet
thoroughly explored for beetles, it is probable that many similar examples
of peculiar isolated forms remain to be discovered.

Looking, then, at what seem to me the probabilities of the case from the
standpoint of evolution and natural selection, and giving due weight to the
facts of local distribution as they are actually presented to us, I am
forced to differ from the opinion held by our best entomological
authorities, and to believe that some at least, perhaps many, of the
species which, in the present state of our knowledge, appear to be peculiar
to our islands, are, not only apparently, but really, so peculiar.

I am indebted to Mr. Robert McLachlan for the following information on
certain Trichopterous Neuroptera (or caddis-flies) which appear to be
confined to our islands. The peculiar aquatic habits of the larvae of these
insects, some living in ponds or rivers, others in lakes, and others again
only in clear mountain streams, render it not improbable that some of them
should have become isolated and preserved in our islands, or that they
should be modified owing to such isolation.

_Trichoptera peculiar to the British Isles._

1. PHILOPOTAMUS INSULARIS. (? A variety of _P. montanus_.)--This can
hardly be termed a British species or variety, because, so far as at
present known, it is peculiar to the Island of Guernsey. It agrees
structurally with _P. montanus_, a species found both in Britain and on
the continent, but it differs in its strikingly yellow colour, and less
pronounced markings. All the specimens from Guernsey are alike, and
resident entomologists assured Mr. McLachlan that no other kind is
known. Strange to say, some examples from Jersey differ considerably,
resembling the common European and British form. Even should this
peculiar variety be at some future time found on the continent it would
still be a remarkable fact that the form of insect inhabiting two small
islands only twenty miles apart should constantly differ; but as Jersey
is between Guernsey and the coast, it seems just possible that the more
insular conditions, and perhaps som