t disturbed relations, and
to bring every species into harmony with the varying conditions of the
surrounding universe.

But even the conjectural explanation now given fails us in the other
cases of local modification. Why the species of the Western islands
should be smaller than those further east,--why those of Amboyna should
exceed in size those of Gilolo and New Guinea--why the tailed species
of India should begin to lose that appendage in the islands, and retain
no trace of it on the borders of the Pacific,--and why, in three
separate cases, the females of Amboyna species should be less gaily
attired than the corresponding females of the surrounding islands,--are
questions which we cannot at present attempt to answer. That they
depend, however, on some general principle is certain, because analogous
facts have been observed in other parts of the world. Mr. Bates informs
me that, in three distinct groups, Papilios which on the Upper Amazon
and in most other parts of South America have spotless upper wings
obtain pale or white spots at Para and on the Lower Amazon; and also
that the AEneas-group of Papilios never have tails in the equatorial
regions and the Amazons valley, but gradually acquire tails in many
cases as they range towards the northern or southern tropic. Even in
Europe we have somewhat similar facts; for the species and varieties of
butterflies peculiar to the island of Sardinia are generally smaller and
more deeply coloured than those of the mainland, and the same has
recently been shown to be the case with the common tortoiseshell
butterfly in the Isle of Man; while Papilio Hospiton, peculiar to the
former island, has lost the tail, which is a prominent feature of the
closely allied P. Machaon.

Facts of a similar nature to those now brought forward would no doubt be
found to occur in other groups of insects, were local faunas carefully
studied in relation to those of the surrounding countries; and they
seem to indicate that climate and other physical causes have, in some
cases, a very powerful effect in modifying specific form and colour, and
thus directly aid in producing the endless variety of nature.

_Mimicry._

Having fully discussed this subject in the preceding essay, I have only
to adduce such illustrations of it, as are furnished by the Eastern
Papilionidae, and to show their bearing upon the phenomena of variation
already mentioned. As in America, so in the Old World, species of
Dana