The Brihad-Aranyaka Upanishad is the oldest of all the Upanishads, and no expert authority would date it later than 800 B.C. In opposition to the prevailing opinion I should not like definitely to deny the possibility of Plato having been dependent, even though very indirectly, on these Indian thoughts, for this possibility cannot be absolutely put aside even for the doctrine of re-incarnation. A dependence of this sort, first conveyed through Pythagoras, would scarcely detract from the significance of the coincidence in thought, for Plato would not have adopted any such story conveyed in some way from Oriental traditions, let alone have given it such an important place, had he not himself felt the truth contained in it to be illuminating. In an article by K. Ziegler (‘Menschen- und Weltwerden’, _Neue Fahrbücher für das klassische Altertum_, 1913, Band XXXI), which contains a systematic investigation of the thought in question, it is traced back to Babylonian ideas. Footnote 36: I would here subjoin a few words to clarify our nomenclature, one which has undergone a certain development in the course of our discussion. What ‘sexual instincts’ are, we knew through their relation to the sexes and to the function of propagation. We then retained this term when the findings of psycho-analysis compelled us to regard its relation to propagation as less close. With the discovery of narcissistic libido, and the extension of the libido concept to the individual cells, the sexual instinct became for us transformed into the Eros that endeavours to impel the separate parts of living matter to one another and to hold them together; what is commonly called the sexual instinct appears as that part of the Eros that is turned towards the object. Our speculation then supposes that this Eros is at work from the beginnings of life, manifesting itself as the ‘life-instinct’ in contradistinction to the ‘death-instinct’ which developed through the animation of the inorganic. It endeavours to solve the riddle of life by the hypothesis of these two instincts striving with each other from the very beginning. The transformation which the concept of the ‘ego-instincts’ has undergone is perhaps harder to review. Originally we applied this term to all those instinct-directions—not better known to us—which can be distinguished from the sexual instincts that have the object as their aim, thus contrasting the ego-instincts with the sexual ones, the expression of which is the libido. Later on we approached the analysis of the ego and saw that a part also of the ‘ego-instincts’ is of a libidinous nature, having taken its own self as an object. These narcissistic instincts of self-preservation therefore had now to be reckoned to the libidinous sexual instincts. The contrast between egoistic and sexual instincts was now converted into one between egoistic and