These far-reaching speculations make the element of keenest interest in the inquiry which follows. But even apart from its possible bearing on a future life, the further study of our submerged mentation,--of the processes within us of which we catch only indirect, and as it were, refracted glimpses,--seems at this time especially called for by the trend of modern research. For of late years we have realised more and more fully upon how shifting and complex a foundation of ancestral experience each individual life is based. In recapitulation, in summary, in symbol, we retraverse, from the embryo to the corpse, the history of life on earth for millions of years. During our self-adaptation to continually wider environments, there may probably have been a continual displacement of the threshold of consciousness;--involving the lapse and submergence of much that once floated in the main stream of our being. Our consciousness at any given stage of our evolution is but the phosphorescent ripple on an unsounded sea. And, like the ripple, it is not only superficial but manifold. Our psychical unity is federative and unstable; it has arisen from irregular accretions in the remote past; it consists even now only in the limited collaboration of multiple groups. These discontinuities and incoherences in the Ego the elder psychologists managed to ignore. Yet infancy, idiocy, sleep, insanity, decay;--these breaks and stagnancies in the conscious stream were always present to show us, even more forcibly than more delicate analyses show us now, that the first obvious conception of man's continuous and unitary personality was wholly insecure; and that if indeed a soul inspired the body, that soul must be sought for far beneath these bodily conditions by which its self-manifestation was clouded and obscured. The difference between older and newer conceptions of the unifying principle or soul (if soul there be) in man, considered as manifesting through corporeal limitations, will thus resemble the difference between the older and newer conceptions of the way in which the sun reveals himself to our senses. Night and storm-cloud and eclipse men have known from the earliest ages; but now they know that even at noonday the sunbeam which reaches them, when fanned out into a spectrum, is barred with belts and lines of varying darkness;--while they have learnt also that where at either end the spectrum fades out into what for us is blackness, there stretches onwards in reality an undiscovered illimitable ray.