We have already touched on the general function of self-consciousness, the gain which accrues to the individual organism from knowing its own experiences as such by giving self-directivity and special response. The individual is thereby enabled to look after its own interests, to consciously care for itself, and to make the most of itself. The core of psychic life is _interest_, and the core of _interest_ is self-consciousness. That the psychism has interest, that it feels for itself, is essential to the progress of life. Indeed, the genesis and growth of biological forms and organs lie in their attainment and perfecting as servants to the self in the struggle of existence. We know this to be the case for the sense-organs. The organism evidently came to appreciate light by a definite _nisus_ with self-consciousness, just the same in kind as that by which organ is advanced to-day when straining the eyes to perceive a seventh Pleiad. In short, we do not see because we have eyes, but we have eyes because we see. The seeing activity and effort as a self-activity generates the eye and perfects it. So also it is by locomotive effort that motor organs originate and develop. The young child learning to walk, self-consciously and with effort moving upon its legs, is an intimation of the way in which the limbs themselves arose in active response to environment. The rabbits imported into Australia have, it is reported, learned to climb trees, with a consequent modification of foot structure. Now the real genesis of the morphological change is obviously psychic, the climbing effort as a valuable function to life under the conditions of existence, viz., the scarcity of herbage.