same logical process was exemplified in the discovery of abdominal ribs in the human embryo.
As long ago as 1801 Blumenbach inferred from the configuration of its skull that ornithorhyncus laid eggs, and his deduction, based on the known correlation of characters, was verified by Caldwell's recent demonstration that the monotremes are egglayers. There was an unverified deduction that monotremes must at some time have possessed normal teeth; it was verified by the recent discovery of calcified teeth in monotreme embryos. "Thatcher showed in 1887 that fins of fishes are derived from two pairs of lateral folds. In a paper on the significance of bone structure Dwight commented on this and said that if evolution were true he could see no reason why no vertebrate had more than four limbs. He also said that he could see no reason why no vertebrate had more than two eyes. In the same year Watase demonstrated that the Japanese goldfish has eight limbs and Spencer showed that all vertebrates have a third eye in the pineal gland. Spencer predicted that fossils would be found in which the pineal eye was functional; Cope demonstrated in fossils the orbit of this third eye and pointed out the attachment of muscles for its movement."[1]
"Evolution suggested the annelids as remote ancestors of the vertebrates. Kowalevsky was thus led to the discovery of germ-layers among these animals—homologous with those of vertebrates. In the same way, but on the other side, Semper was led to the discovery of genuine worm kidneys (nephridia) in the lower fishes. Starting with the theory of genetic affinity, we have discovered a whole series of organs and tissues that had hitherto remained unknown. For example, we have now the 'spinal ganglia' in worms, the 'spinal nerves,' and, what is perhaps more important, we have discovered the sense organs out of which the sense organs of the vertebrates have been gradually built up."[2]
One of the best-defined anticipations, and one that found confident expression from different sources, in the way of special predictions, long before it was verified, was the belief that primitive mammals were generalized types. Cope wrote, March, 1874, "I trust that I have made it sufficiently obvious that the primitive genera of this division of mammals (Mammalia educabilia) must have been bunodonts with pentadactyl plantigrade feet."[3] "No perissodactyl or artiodactyl mammal was known at that time to possess such feet, nor was any perissodactyl known to possess tubercular teeth." Since the prediction was made, Cope has described nine species of the Eocene genus Phenacodus, "prob-
