truction. Mr. Bates may
almost be said to have actually witnessed the process by which the
mimickers have come so closely to resemble the mimicked; for he
found that some of the forms of Leptalis which mimic so many other
butterflies, varied in an extreme degree. In one district several
varieties occurred, and of these one alone resembled, to a certain
extent, the common Ithomia of the same district. In another district
there were two or three varieties, one of which was much commoner than
the others, and this closely mocked another form of Ithomia. From facts
of this nature, Mr. Bates concludes that the Leptalis first varies; and
when a variety happens to resemble in some degree any common butterfly
inhabiting the same district, this variety, from its resemblance to a
flourishing and little persecuted kind, has a better chance of escaping
destruction from predaceous birds and insects, and is consequently
oftener preserved; "the less perfect degrees of resemblance being
generation after generation eliminated, and only the others left to
propagate their kind." So that here we have an excellent illustration of
natural selection.

Messrs. Wallace and Trimen have likewise described several equally
striking cases of imitation in the Lepidoptera of the Malay Archipelago
and Africa, and with some other insects. Mr. Wallace has also detected
one such case with birds, but we have none with the larger quadrupeds.
The much greater frequency of imitation with insects than with other
animals, is probably the consequence of their small size; insects cannot
defend themselves, excepting indeed the kinds furnished with a sting,
and I have never heard of an instance of such kinds mocking other
insects, though they are mocked; insects cannot easily escape by
flight from the larger animals which prey on them; therefore, speaking
metaphorically, they are reduced, like most weak creatures, to trickery
and dissimulation.

It should be observed that the process of imitation probably never
commenced between forms widely dissimilar in colour. But, starting with
species already somewhat like each other, the closest resemblance,
if beneficial, could readily be gained by the above means, and if
the imitated form was subsequently and gradually modified through any
agency, the imitating form would be led along the same track, and thus
be altered to almost any extent, so that it might ultimately assume an
appearance or colouring wholly unlike that o