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If we are to take the topography of mental acts seriously we must direct our interest to a doubt which arises at this point. When a psychical act (let us confine ourselves here to one which is in the nature of an idea) is transposed from the system Ucs. into the system Cs. (or Pcs.), are we to suppose that this transposition involves a fresh record - as it were, a second registration - of the idea in question, which may thus be situated as well in a fresh psychical locality, and alongside of which the original unconscious registration continues to exist? Or are we rather to believe that the transposition consists in a change in the state of the idea, a change involving the same material and occurring in the same locality? This question may appear abstruse, but it must be raised if we wish to form a more definite conception of psychical topography, of the dimension of depth in the mind. It is a difficult one because it goes beyond pure psychology and touches on the relations of the mental apparatus to anatomy. We know that in the very roughest sense such relations exist. Research has given irrefutable proof that mental activity is bound up with the function of the brain as it is with no other organ. We are taken a step further - we do not know how much - by the discovery of the unequal importance of the different parts of the brain and their special relations to particular parts of the body and to particular mental activities. But every attempt to go on from there to discover a localization of mental processes, every endeavour to think of ideas as stored up in nerve-cells and of excitations as travelling along nerve-fibres, has miscarried completely. The same fate would await any theory which attempted to recognize, let us say, the anatomical position of the system Cs. - conscious mental activity - as being in the cortex, and to localize the unconscious processes in the sub-cortical parts of the brain. There is a hiatus here which at present cannot be filled, nor is it one of the tasks of psychology to fill it. Our psychical topography has for the present nothing to do with anatomy; it has reference not to anatomical localities, but to regions in the mental apparatus, wherever they may be situated in the body.