FIG. 7.—Cæcum and vermiform appendage of the chimpanzee (from a preparation in the Paris Museum of Natural History). ] It is not surprising, in the face of resemblances so numerous, that forty years’ science has proclaimed the existence of a close affinity between man and the anthropoid apes. The view has become an established doctrine, now that no single fact has been brought against it. Since the theory was enunciated we have learned much regarding the natural history of these apes. Generally, when a theory is false, a new set of facts overthrows it. Attempts may be made to trim the new facts to the existing theory, but such attempts are doomed to failure, and the theory disappears. It is of special interest, then, to confront the simian theory of the origin of man with a series of facts gathered by science since the theory was propounded. When Huxley wrote, the embryological history of anthropoid apes was practically unknown. Darwin, Vogt, and Haeckel, in their attempts to support the theory of the animal origin of man, had not sufficient knowledge of the embryology of monkeys. It is only recently that important work on this subject has been published. It is known that the history of development is very often an excellent guide in tracing the relationship of organisms. It is therefore interesting to examine the established facts concerning the embryology of anthropoid apes. The material for these studies is very difficult to obtain, and it is not astonishing that even our present state of knowledge is still imperfect. [Illustration: FIG. 8.—Fœtus of gibbon (after Selenka). ] The placenta often gives information of great importance in the classification of mammals. It is sufficient to glance at the zonary placenta of dogs and seals to be convinced of the relationship of these two species, which at first sight seem so different. Now, the placentas of all the anthropoid apes examined up to the present are of the same discoid type as that of man. The arrangement of the umbilical cord of man, which was formerly considered as quite peculiar to him, is found in anthropoid apes, as has been established by Deniker[56] and Selenka[57] It is striking that the anthropoids resemble man rather than the lower monkeys in the relation of the fœtus to the fœtal membranes. [Illustration: FIG. 9.—Human fœtus of three months and a half. ] With regard to the embryos themselves, the similarity between those of monkeys and of man is very great. Selenka insists on the fact that the youngest stages of human development that have been obtained can hardly be distinguished from those of the lower monkeys either in position or in shape. More advanced stages exhibit greater differentiation, and the later embryos of man resemble those of anthropoids much more closely than those of the lower monkeys. The fœtus of the gibbon, figured by Selenka (Fig. 8), presents the most striking likeness to a corresponding human fœtus (Fig. 9).