The proofs that are relied upon to establish the operation and effect of these agencies in producing the results that are claimed for them, ought to show that, in one or more instances, an animal of a superior organization which, when left to the natural course of its reproduction by the union of its two sexes, always produces its own distinct type and no other, has, in fact, been itself evolved out of some lower and different organism by the agencies of natural and sexual selection operating among the individuals of that lower type. One of the proofs, on which great stress is laid by Mr. Darwin, may be disposed of without difficulty. It is that which is said to take place in the breeding of domestic animals, or of animals the breeding of which man undertakes to improve for his own practical benefit, or to please his fancy, or to try experiments. In all that has been done in this kind of selection, in breeding from the best specimens of any class of animals, there is not one instance of the production of an animal varying from its near or its remote known progenitors in anything but adventitious peculiarities which will not warrant us in regarding it as a new or different animal. No breeder of horses has ever produced an animal that was not a horse. He may have brought about great and important improvements in the qualities of fleetness, or strength, or weight, or endurance, by careful selection of the sire and the dam; but the race-horse or the hunter, or the draught-horse or the war-horse, is but a horse of different qualities and powers, with the same skeleton, viscera, organs, muscles, which mark this species of animal, and with no other variations of structure than such as follow from the limited development of different parts for different uses. No breeder of cows ever produced a female animal that was not a cow, although he may have greatly improved the quality and quantity of the milk peculiar to this animal by careful selection of the individuals which he permits or encourages to breed. No breeder of sheep ever produced an animal that was not a sheep, although the quality of the fleece or of the mutton may have been greatly improved or varied. Among the domestic fowls, no animal that was not a bird was ever bred by any crossing of breeds, although great varieties of plumage, structure of beak, formation of foot, development of wing, habits of life, adaptation to changes of situation, and many minor peculiarities, have been the consequences of careful and intelligent breeding from different varieties of the same fowl. In the case of the pigeon, of which Mr. Darwin has given a great many curious facts from his own experience as a breeder, the most remarkable variations are perhaps to be observed as the results of intentional breeding from different races of that bird; but with all these variations nothing that was not a bird was ever produced. In the case of the dog, whatever was his origin, or supposing him to