Though the philosophy of Agassiz and the rest has not, however, been dissipated in thin air, we have an idea, nevertheless, that it has failed, like the Trojan’s arrow. We “cannot away with” that notion of making a species of man for every extreme climate of the globe, and do not think they have at all made the matter clear. They argue analogically. Their opponents argue analogically too. Pritchard and others support their views of the unity of the human species by the analogy of animals. They bring forward a very strong argument in the fact, that hybrids of plants or animals—the offspring of different species—are sterile, as a general law of nature. The offspring of the most dissimilar races of men are never hybrid—but capable of continuing the kind. Pritchard says the difference between the skull of the domestic hog and that of the wild boar is as great as that between the European and Negro skulls; and Blumenbach says there is more difference between the skulls of the Neapolitan and Hungarian breed of horses, respectively, than between the most dissimilar human heads. But those who agree with Agassiz rely a good deal upon the assertions of Dr. Morton, of Philadelphia, and adduce several instances in which hybrids were found to be fruitful—mostly, however, in conjunction with an animal of pure stock. Still, these cases are so exceptional, or so uncertain, that no general conclusion can be drawn from them, sufficient to make head against Pritchard, Buffon, Cuvier, Hunter, and those who argue with them, on the matter. The general law is the true one. A man has suckled an infant, and a heifer, that never calved, has given milk; but such things cannot tell against the order of Nature.