k dot in the centre
denote birds with a small amount of pigment.]

An essential feature of the case of the currant moth lies in the different
results given by reciprocal crosses. _Lacticolor_ female x _grossulariata_
male gives _grossulariata_ alone of both sexes. But _grossulariata_ female
x _lacticolor_ male gives only _grossulariata_ males and _lacticolor_
females. Such a difference between reciprocal crosses has also been found
in other animals, and the experimental results, though sometimes more
complicated, are explicable on the same lines. An interesting case in which
three factors are concerned has been recently worked out in poultry. The
Silky breed of fowls is characterised among other peculiarities by a
remarkable abundance of melanic pigment. The skin is dull black, while the
comb and wattles are of a deep purple colour contrasting sharply with the
white plumage (Pl. V., 3). Dissection shows that this black pigment is
widely spread throughout the body, being especially marked in such
membranes as the mesenteries, the periosteum, and the pia mater surrounding
the brain. It also occurs in the connective tissues among the muscles. In
the Brown Leghorn, on the other hand, this pigment is not found. Reciprocal
crosses between these two breeds gave a remarkable difference in result. A
cross between the Silky hen and the Brown Leghorn cock produced F_1 birds
in which both sexes exhibited only traces of the pigment. On casual
observation they might have {106} passed for unpigmented birds, for with
the exception of an occasional fleck of pigment their skin, comb and
wattles were as clear as in the Brown Leghorn (Pl. V., 1 and 4). Dissection
revealed the presence of a slight amount of internal pigment. Such birds
bred together gave some offspring with the full pigmentation of the Silky,
some without any pigment, and others showing different degrees of pigment.
None of the F_2 male birds, however, showed the full deep pigmentation of
the Silky.

[Illustration: FIG. 20.

Scheme illustrating the result of crossing a Brown Leghorn hen with a Silky
cock (cf. Fig. 19).]

When, however, the cross was made the other way, viz. Brown Leghorn hen x
Silky cock, the result was different. While the F_1 male birds were almost
destitute of pigment as in the previous cross, the F_1 hens, on the other
hand, were nearly as deeply pigmented as the pure Silky {107} (Pl. V., 2).
The male Silky transmitted the pigmentation, but only to h