There are something over 150 different varieties of the domestic pigeon. Some of these varieties—as many as a dozen, Mr. Darwin thinks—differ from each other sufficiently to be reckoned, if they are considered solely with reference to their structures, as entirely distinct species. The carrier, for instance, the giant of the pigeons, measures 17 inches from bill-tip to the end of its tail, and has a beak 1 3/4 inches long. Around each eye is a large dahlia-like wattle, and another large wattle is on the beak, giving the beak the appearance of having been thrust through the kernel of a walnut. The tumbler is small, squatty, and almost beakless. It has the preposterous habit of rising high in the air and then tumbling heels over head. The roller, one of the many varieties of the tumbler, descends to the ground in a series of back somersaults, executed so rapidly that it looks like a falling ball. The runt is large, weighing sometimes as much as the carrier. The fantail has thirty or forty feathers in its tail, while all other varieties have only twelve or fourteen, the normal number for birds. The trumpeter, so named on account of its peculiar coo, has an umbrella-like hood of feathers covering its head and face, and its feet are so heavily feathered that they look like little wings. In the correct specimens of this variety the feathers have to be clipped from the face before the birds can see to feed themselves. The pouter has the absurd habit of inflating its gullet to a prodigious size, and the Jacobin wears a gigantic ruff. The homing pigeon has such a strong attachment for its cote that it will travel hundreds of miles, sometimes as many as 1,400 miles, in order to reach the home from which it has been separated. But it is not simply in their colour, size, habits, and plumage, that pigeons vary. There are corresponding differences in their structures, in the number of their ribs and vertebrae, in the shape and size of the skull, in the bones of the face, in the development of the breast-bone, and in the length of the neck, legs, and bill. Pigeons also differ in the shape and size of their eggs, and in their dispositions and voice. ‘There is,’ says Huxley in summing up his discussion of the great variety in these birds, ‘hardly a particular of either internal economy or external shape which has not by selective breeding been perpetuated and become the foundation of a new race’.[7] All of the 150 different varieties of domestic pigeons have been evolved by human selection during the past three or four thousand years from the blue rock-doves which to-day inhabit the seacoast countries of Europe.