The wings have two black bars.

Some semi-domestic breeds, and some truly wild breeds, have, besides the two black bars, the wings chequered with black.

These several marks do not occur together in any other species of the whole family.

Now, in every one of the domestic breeds, taking thoroughly well-bred birds, all the above marks, even to the white edging of the outer tail-feathers, sometimes concur perfectly developed.

Moreover, when birds belonging to two or more distinct breeds are crossed, none of which are blue or have any of the above-specified marks, the mongrel offspring are very apt suddenly to acquire these characters.