n terms of definite physiological factors, and the diversity of animal and
plant life is due to the gain or loss of these factors, to the origination
of new ones, or to fresh combinations among those already in existence. Nor
is there any valid reason against the supposition that even the most
remarkable cases of resemblance, such as that of the leaf insect, may have
arisen through a process of mutation. Experience with domestic plants and
animals shows that the most bizarre forms may arise as sports and
perpetuate themselves. Were such forms, arising under natural conditions,
to be favoured by natural selection owing to a resemblance to something in
their environment we should obtain a striking case of protective
adaptation. And here it must not be forgotten that those striking cases to
which our attention is generally called are but a very small minority of
the existing forms of life.

For that special group of adaptation phenomena classed under the head of
Mimicry, Mendelism seems to offer an interpretation simpler than that at
present in vogue. This perhaps may be more clearly expressed by taking a
specific case. There is in Africa a genus of Danaine butterflies known as
_Amauris_, and there are reasons for considering that the group to which it
belongs possesses properties which render it unpalatable to vertebrate
enemies such as birds or monkeys. In the same region is also found the
genus _Euralia_ belonging to the entirely {145} different family of the
Nymphalidae, to which there is no evidence for assigning the disagreeable
properties of the Danaines. Now the different species of _Euralia_ show
remarkably close resemblances to the species of _Amauris_, which are found
flying in the same region, and it is supposed that by "mimicking" the
unpalatable forms they impose upon their enemies and thereby acquire
immunity from attack. The point at issue is the way in which this seemingly
purposeful resemblance has been brought about.

One of the species of _Euralia_ occurs in two very distinct forms (Pl.
VI.), which were previously regarded as separate species under the names
_E. wahlbergi_ and _E. mima_. These two forms respectively resemble
_Amauris dominicanus_ and _A. echeria_. For purposes of argument we will
assume _A. echeria_ to be the more recent form of the two. On the modern
Darwinian view certain individuals of _A. dominicanus_ gradually diverged
from the _dominicanus_ type and eventually reached the _echeria_