lly admitted opinion
that a new type has been developed in the United States, and this in about
a couple of centuries only, and in a vast multitude of individuals of {89}
diverse ancestry. The instances here given, however, must suffice, though
more could easily be added.

[Illustration: THE GREAT SHIELDED GRASSHOPPER.]

It may be well now to turn to groups presenting similar variations, not
through, but independently of, geographical distribution, and, as far as we
know, independently of conditions other than some peculiar nature and
tendency (as yet unexplained) common to members of such groups, which
nature and tendency seem to induce them to vary in certain definite lines
or directions which are different in different groups. Thus with regard to
the group of insects, of which the walking leaf is a member, Mr. Wallace
observes:[69] "The _whole family_[70] of the Phasmidae, or spectres, to
which this insect belongs, is more or less imitative, and a great number of
the species are called 'walking-stick insects,' from their singular {90}
resemblance to twigs and branches."

[Illustration: THE SIX-SHAFTED BIRD OF PARADISE.]

Again, Mr. Wallace[71] tells us of no less than four kinds of orioles,
which birds mimic, more or less, four species of a genus of honey-suckers,
the weak orioles finding their profit in being mistaken by certain birds of
prey for the strong, active, and gregarious honey-suckers. Now, many other
birds would be benefited by similar mimicry, which is none the less
confined, in this part of the world, to the oriole genus. It is true that
the absence of mimicry in other forms may be explained by their possessing
some other (as yet unobserved) means of preservation. But it is
nevertheless remarkable, not so much that one species should mimic, as that
no less than four should do so in different ways and degrees, all these{91}
four belonging to _one and the same genus_.

[Illustration: THE LONG-TAILED BIRD OF PARADISE.]

In other cases, however, there is not even the help of protective action to
account for the phenomenon. Thus we have the wonderful birds of
Paradise,[72] which agree in developing plumage unequalled in beauty, but a
beauty which, as to details, is of different kinds, and produced in
different ways in different species. To develop "beauty and singularity of
plumage" is a character of the group, but not of any one definite kind, to
be explained merely by inheritance.