discussing is one of which
comparatively little is really known. The natural history of the tropics
has never yet been studied on the spot with a full appreciation of "what
to observe" in this matter. The varied ways in which the colouring and
form of animals serve for their protection, their strange disguises as
vegetable or mineral substances, their wonderful mimicry of other
beings, offer an almost unworked and inexhaustible field of discovery
for the zoologist, and will assuredly throw much light on the laws and
conditions which have resulted in the wonderful variety of colour,
shade, and marking which constitutes one of the most pleasing
characteristics of the animal world, but the immediate causes of which
it has hitherto been most difficult to explain.

If I have succeeded in showing that in this wide and picturesque domain
of nature, results which have hitherto been supposed to depend either
upon those incalculable combinations of laws which we term chance or
upon the direct volition of the Creator, are really due to the action
of comparatively well-known and simple causes, I shall have attained my
present purpose, which has been to extend the interest so generally felt
in the more striking facts of natural history to a large class of
curious but much neglected details; and to further, in however slight a
degree, our knowledge of the subjection of the phenomena of life to the
"Reign of Law."

IV.

THE MALAYAN PAPILIONIDAE OR SWALLOW-TAILED BUTTERFLIES, AS ILLUSTRATIVE
OF THE THEORY OF NATURAL SELECTION.

_Special Value of the Diurnal Lepidoptera for enquiries of this nature._

When the naturalist studies the habits, the structure, or the affinities
of animals, it matters little to which group he especially devotes
himself; all alike offer him endless materials for observation and
research. But, for the purpose of investigating the phenomena of
geographical distribution and of local, sexual, or general variation,
the several groups differ greatly in their value and importance. Some
have too limited a range, others are not sufficiently varied in specific
forms, while, what is of most importance, many groups have not received
that amount of attention over the whole region they inhabit, which could
furnish materials sufficiently approaching to completeness to enable us
to arrive at any accurate conclusions as to the phenomena they present
as a whole. It is in those groups which are, and have long been,