He crossed some white fantails with some black barbs, and the mongrels were black, brown, or mottled.

He also crossed a barb with a spot, which is a white bird with a red tail and red spot on the forehead, and the mongrel offspring were dusky and mottled.

On now crossing these two sets of mongrels with each other, he obtained a bird of a beautiful blue colour, with the barred and white edged tail, and double-banded wings, so as almost exactly to resemble a wild rock-pigeon.

This bird was descended in the second generation from a pure white and pure black bird, both of which when unmixed breed their kind remarkably true.

These facts, well known to experienced pigeon-fanciers, together with the habits of the birds, which all like to nest in holes, or dovecots, not in trees like the great majority of wild pigeons, have led to the general belief in the single origin of all the different kinds.
In order to afford some idea of the great differences which exist among domesticated pigeons, it will be well to give a brief abstract of Mr.
Darwin's account of them.