number of breeds and sub-breeds, and in these the sexes generally
differ in plumage; so that it has been noticed as an unusual
circumstance when in certain sub-breeds they resemble each other. On
the other hand, the domestic pigeon has likewise produced a vast number
of distinct breeds and sub-breeds, and in these, with rare exceptions,
the two sexes are identically alike.
Therefore if other species of Gallus and Columba were domesticated and
varied, it would not be rash to predict that similar rules of sexual
similarity and dissimilarity, depending on the form of transmission,
would hold good in both cases. In like manner the same form of
transmission has generally prevailed under nature throughout the same
groups, although marked exceptions to this rule occur. Thus within the
same family or even genus, the sexes may be identically alike, or very
different in colour. Instances have already been given in the same
genus, as with sparrows, fly-catchers, thrushes and grouse. In the
family of pheasants the sexes of almost all the species are wonderfully
dissimilar, but are quite alike in the eared pheasant or Crossoptilon
auritum. In two species of Chloephaga, a genus of geese, the male
cannot be distinguished from the females, except by size; whilst in two
others, the sexes are so unlike that they might easily be mistaken for
distinct species. (29. The Ibis, vol. vi. 1864, p. 122.)
The laws of inheritance can alone account for the following cases, in
which the female acquires, late in life, certain characters proper to
the male, and ultimately comes to resemble him more or less completely.
Here protection can hardly have come into play. Mr. Blyth informs me
that the females of Oriolus melanocephalus and of some allied species,
when sufficiently mature to breed, differ considerably in plumage from
the adult males; but after the second or third moults they differ only
in their beaks having a slight greenish tinge. In the dwarf bitterns
(Ardetta), according to the same authority, the male acquires his
final livery at the first moult, the female not before the third or
fourth moult; in the meanwhile she presents an intermediate garb, which
is ultimately exchanged for the same livery as that of the male. So
again the female Falco peregrinus acquires her blue plumage more slowly
than the male. Mr. Swinhoe states that with one of the Drongo shrikes
(Dicrurus macrocercus) the male, whilst almost a nestling, moults his
soft brown plumage and becomes of a uniform glossy greenish-black; but
the female retains for a long time the white striae and spots on the
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