But the most important of all the recent palaeontological discoveries which have served to elucidate the origin of the placentals relate to our own stem, the legion of primates. Formerly fossil remains of the primates were very scarce. Even Cuvier, the great founder of palaeontology, maintained until his last day (1832) that there were no fossilized primates; he had himself, it is true, described the skull of an Eocene prosimiæ (_adapis_), but he had wrongly classed it with the ungulata. However, during the last twenty years a fair number of well-preserved fossilized skeletons of prosimiæ and simiæ have been discovered; in them we find all the chief intermediate members which complete the connecting chain of ancestors from the oldest prosimiæ to man. The most famous and most interesting of these discoveries is the fossil ape-man of Java, the much-talked-of _pithecanthropus erectus_, found by a Dutch military doctor, Eugen Dubois, in 1894. It is in truth the much-sought "missing link," supposed to be wanting in the chain of primates, which stretches unbroken from the lowest catarrhinæ to the highest-developed man. I have dealt exhaustively with the significance of this discovery in the paper which I read on August 26, 1898, at the Fourth International Zoological Congress at Cambridge.[13] The palæontologist, who knows the conditions of the formation and preservation of fossils, will think the discovery of the pithecanthropus an unusually lucky accident. The apes, being arboreal, seldom came into the circumstances (unless they happened to fall into the water) which would secure the preservation and petrifaction of their skeleton. Thus, by the discovery of this fossil man-monkey of Java the descent of man from the ape has become just as clear and certain from the palæontological side as it was previously from the evidence of comparative anatomy and ontogeny. We now have all the principal documents which tell the history of our race. CHAPTER VI THE NATURE OF THE SOUL Fundamental Importance of Psychology--Its Definition and Methods--Divergence of Views Thereon--Dualistic and Monistic Psychology--Relation to the Law of Substance--Confusion of Ideas--Psychological Metamorphoses: Kant, Virchow, Du Bois-Reymond--Methods of Research of Psychic Science--Introspective Method (Self-Observation)--Exact Method (Psycho-Physics)--Comparative Method (Animal Psychology)--Psychological Change of Principles: Wundt--Folk-Psychology and Ethnography: Bastian--Ontogenetic Psychology: Preyer--Phylogenetic Psychology: Darwin, Romanes