anan White's clever
little essay on distribution. And, as I remarked before, his conclusions
are somewhat marred by the unwarrantable assumption that our islands at
no distant date were totally destitute of all plant-life, and were
therefore uninhabitable by animals. But his paper differs in so far from
most of the others, that he has made a thorough study of the one group
he deals with. In some respects it may serve as a model to future
students in its general treatment of the problem he has set himself to
work out. He adopts the principle, even for butterflies, that though it
is possible for them to be blown over from the Continent, they have
probably migrated with the rest of our indigenous fauna and flora across
the dry bed of the German Ocean. His conclusions are that Britain
derived its butterfly fauna from continental Europe in post-glacial
times, that the Arctic and Alpine species were the first arrivals, and
that one part of the Irish species reached Ireland by way of Scotland,
another from the south. He assumes, of course, that Great Britain and
Ireland were connected at that time.

Within the last few years the spell which has bound naturalists to
accept the theory of a total destruction of life during the Glacial
period is happily vanishing, and more enlightened views are gaining
ground. The Lusitanian species of plants in the west of Ireland, which
had already furnished Forbes with an argument in favour of survival, are
also regarded by Mr. Bulman as the remnants of a pre-glacial flora which
was exterminated everywhere else by the cold (p. 265). This view of the
survival of a pre-glacial fauna and flora has since been accepted by Mr.
Carpenter, whilst I also have endeavoured to bring fresh evidence into
the field in its favour. We both agree with Edward Forbes in considering
the Lusitanian element as the oldest section of our fauna and flora, and
that it came long before the Glacial period. But we differ somewhat from
him, in so far as we do not limit that element to Ireland. It seems also
to be represented in South-western England and Wales, though it is there
less conspicuous.

This decision as to the relative age of the British South-western fauna
has not been arrived at from any geological considerations. The
conviction that it must be older than the other sections has been gained
solely from a study of the geographical distribution of the species
belonging to that fauna. Many of them exhibit what is k