Looking at the matter from the evolutionary point of view, the question among sensations was one of the development of the fittest; that is to say that, as the organism became more complex and needed sensations more definite than sufficed for the protozoon, certain sensibilities got themselves defined and stereotyped upon the organism by the evolution of end-organs.[80] Others failed to get thus externalised; but may, for aught we know, persist nevertheless in the central organs;--say, for instance, in what for man are the optic or olfactory tracts of the brain. There will then be no apparent reason why these latent powers should not from time to time receive sufficient stimulus, either from within or from without, to make them perceptible to the waking intelligence, or perceptible at least in states (like trance) of narrow concentration. As the result of these considerations, I approach alleged heteræsthesiæ of various kinds with no presumption whatever against their real occurrence. Yet on the other hand, my belief in the extent of possible _hyperæsthesia_ continually suggests to me that the apparently new perceptions may only consist of a mixture of familiar forms of perception, pushed to a new extreme, and centrally interpreted with a new acumen, while there is no doubt that many experiments supposed to furnish evidence of such new perceptions merely illustrate the effect of suggestion or self-suggestion. Without, however, presuming to criticise past evidence wholesale, I yet hope that the experience now attained may lead to a much greater number of well-guarded experiments in the near future. In Appendix V.A, I very briefly present the actual state of this inquiry. In default of any logical principle, I shall there divide these alleged forms of sensibility according as they are excited by inorganic objects on the one hand, or by organisms (dead or living) on the other. In the meantime I pass on to that group of the dynamogenic effects of suggestion which affect the more central vital operations--either the vaso-motor system, or the neuro-muscular system, or the central sensory tracts. The effects of suggestion on character--induced changes to which we can hardly guess the nervous concomitant--will remain to be dealt with later.