beneficial, is a highly complex affair; and that there is nothing
strange in a transition not having occurred in any particular case.

Lastly, more than one writer has asked why have some animals had their
mental powers more highly developed than others, as such development
would be advantageous to all? Why have not apes acquired the
intellectual powers of man? Various causes could be assigned; but as
they are conjectural, and their relative probability cannot be weighed,
it would be useless to give them. A definite answer to the latter
question ought not to be expected, seeing that no one can solve the
simpler problem, why, of two races of savages, one has risen higher in
the scale of civilisation than the other; and this apparently implies
increased brain power.

We will return to Mr. Mivart's other objections. Insects often resemble
for the sake of protection various objects, such as green or decayed
leaves, dead twigs, bits of lichen, flowers, spines, excrement of birds,
and living insects; but to this latter point I shall hereafter recur.
The resemblance is often wonderfully close, and is not confined to
colour, but extends to form, and even to the manner in which the insects
hold themselves. The caterpillars which project motionless like dead
twigs from the bushes on which they feed, offer an excellent instance of
a resemblance of this kind. The cases of the imitation of such objects
as the excrement of birds, are rare and exceptional. On this head,
Mr. Mivart remarks, "As, according to Mr. Darwin's theory, there is a
constant tendency to indefinite variation, and as the minute incipient
variations will be in ALL DIRECTIONS, they must tend to neutralize
each other, and at first to form such unstable modifications that it is
difficult, if not impossible, to see how such indefinite oscillations
of infinitesimal beginnings can ever build up a sufficiently appreciable
resemblance to a leaf, bamboo, or other object, for natural selection to
seize upon and perpetuate."

But in all the foregoing cases the insects in their original state
no doubt presented some rude and accidental resemblance to an object
commonly found in the stations frequented by them. Nor is this at
all improbable, considering the almost infinite number of surrounding
objects and the diversity in form and colour of the hosts of insects
which exist. As some rude resemblance is necessary for the first start,
we can understand how it is that the larger