es its value? Are there any qualities which, whether
the bird is mature or immature, whether it is untrained or has acquired
fuller expression by practice, whether it inhabits this district or
that, are alike constant? Well, no matter how great the variation, no
matter how much this voice falls below or exceeds the standard, judged
from the human standpoint, attained by that, even we, with our duller
perception, have no difficulty in recognising the species to which the
owner of the voice belongs; in other words, the song is always specific,
and this is the most noticeable, as it is the most remarkable,
characteristic.

There is still, however, another quality to which I would draw
attention--that of loudness. The sounds produced are on the whole alike
penetrative, and the individuals of any given district, even though the
climate by affecting their vocal muscles may have modified the character
of the song, are at no disadvantage in this respect; neither are the
females on the same account the less likely to hear the undeveloped
voice of the immature male.

We have then the following considerations: firstly, there is the
widespread and remarkable phenomenon of imitation, from which we can
infer that the diversity of song is not due to structural differences
but must be sought in some innate capacity to play one tune in
preference to another; secondly, not all the individuals of the same
species play a similar tune--we find that there is in certain directions
a noticeable variation which nevertheless does not seem to affect the
question of success or failure in the attainment of reproduction; in the
third place, in contrast with this variation, we can observe a striking
uniformity in two important particulars, namely in the specific
character and penetrative power of the song--qualities which we know are
essential for the purposes of "recognition" and "warning"; and finally,
from the general course of our investigation, we can infer that if a
male had no certain means of advertising its position, the territory
would not be brought into useful relation in its life. Have we here
sufficient ground on which to construct a theory of origin; in other
words, has the evolution of song been incidental to, and contributory
to, the evolution of the territory?

We have all along spoken of the song and of the call-notes as if they
were manifestations of separate emotional states having their respective
and well-defined spheres of