in fowls castration does not prevent the development of the colour and
form of the male plumage, nor of the spurs: that in drakes, although
castration does not seem to have been carried out on young specimens
before the male plumage was developed, when performed on the mature bird
it prevents the eclipse, and does not cause the male to resemble the hen.
Castration, then, tends to prove that in Birds the development of the male
characters is not so closely dependent on the stimulation of testicular
hormone as in Mammals. The characters must therefore be developed by
heredity in the soma, which implies that the soma must itself be
differentiated in the two sexes. The development must therefore be more
in the nature of gametic coupling. It does not follow that the primary
sex-character or the somatic characters are exclusive in either sex.
We may suppose that the zygote contains both sexes, one or other of which
is dominant, and that dominance of one primary sex involves dominance of
the corresponding sexual characters. This does not, however, agree with
the result of removal of the ovaries in ducks, for this causes the
characters of the male to appear, so that the dominance of the female is
not a permanent condition of the soma but is dependent on the ovarian
hormone.

In the hermaphrodite individuals mentioned above the difference of
dominance is on two sides of the body instead of two different
individuals. It may also be remarked here that while it is very difficult
to believe that spurs were not due in evolution to the mechanical
stimulation of striking with the legs in combat, and while specially
enlarged feathers are erected in display, we cannot at present attribute
the varied and brilliant _colour_ of male birds to the direct influence of
external stimuli.

In Lepidoptera among insects the evidence concerning castration tends to