Thus we see that nearly every part of the body of the pigeon has varied under domestication in the most diverse ways, and to a high degree; and the same is true of several other domesticated animals, poultry, horses, sheep, cattle, pigs, and so on, though the matter is not altogether so clear in their case, since descent from a single wild species cannot be proved, and is in many cases improbable. But in the case of pigeons this common descent is certain, and we have now to inquire in what manner all these variations from the parent form have been brought about. The answering of this question is rendered easier by the fact that new breeds arise even now, and that, to some extent at least, they can be caused to arise, consciously and intentionally. In England, as well as in Germany and France, there are associations for the breeding of birds, and in England especially pigeon and poultry clubs are numerous and highly developed. These by no means confine themselves to simply preserving the purity of existing breeds, they are continually striving to improve them, by increasing and accentuating their characters, or even by introducing quite new qualities, and in many cases they succeed even in this last. Prizes are offered for particular new variations, and thus a spirit of rivalry is fostered among the breeders, and each strives to produce the desired character as quickly as possible. Darwin says: 'The English judges decided that the comb of the Spanish cock, which had previously hung limply down, should stand erect, and in five years this end was achieved; they ordained that hens should have beards, and six years later fifty-seven of the groups of hens exhibited at the Crystal Palace in London were bearded.' The transformation does not always come about so quickly, however; thus, for instance, it required thirteen years before a certain breed of tumblers was furnished with a white head. But the breeders cause every visible part of the body to vary as seems good to them, and within the last fifty years they have really brought about very considerable changes in many breeds. Their method of procedure is carefully to select for breeding those birds which already possess a faint beginning of the desired character. Domesticated animals have on the whole a higher degree of variability than wild species, and the breeder takes advantage of this. Suppose it is a question of adding a crown of feathers to a smooth-headed breed, a bird is chosen which has the feathers on the back of the head a little longer than usual, and mated for breeding. Among its descendants there will probably be some which also exhibit these slightly prominent feathers, and possibly there may be one or other of them which has these feathers considerably lengthened. This one is then used for breeding, and by continually proceeding thus, and selecting for breeding, from generation to generation, only the individuals which approach most nearly to the desired end, the