We seem also to be led to the conclusion, both from _a priori_ considerations and from the results of observation, that effective consciousness is associated with a nervous system. Its fundamental characteristic is control over the actions, so that some kinds of behaviour may be carried out with increased vigour, and others checked. And it is difficult to see how this can take place unless the centres of control are different from those over which they exercise this influence. If we are to understand anything definite by the guidance of consciousness, we must conceive it as standing apart from and exercising an overruling influence over that which it guides. This is unquestionably an essential characteristic of consciousness, as generally understood by those who take the trouble to consider its relation to behaviour; and though some would seek to persuade us that a mere accompaniment of consciousness can somehow determine the continuance or discontinuance of organic behaviour, it is difficult to see how this can be the case. The accompaniment of air-tremors can no more influence the vibrations of a sounding string than an accompaniment of consciousness can affect the nature of the organic changes in the tentacles of the Sun-dew leaf. And if, instead of trusting to such general _a priori_ considerations, we study with attention the conditions under which an animal so behaves as to lead us to infer that it profits by experience, we find that it is not the consciousness that accompanies the behaviour which leads to future guidance, but the consciousness that arises from the results of the behaviour. Let us willingly grant that the newly hatched, and as yet inexperienced chick, when it pecks at a small object is conscious of a visual impression, and is conscious also of movements of its neck and beak. These do not constitute the experience by which it profits. This is provided by the results of the pecking, according as the morsel seized is nice or nasty. We may say, in popular language, that the little bird remembers when it sees a similar object that the former results were pleasant or distasteful, as the case may be; and that it is through this remembrance that future guidance is rendered possible. But all the evidence that we possess goes to show that the sensory centres, stimulated by what we will assume to be the taste of the morsel, are different from those which are affected by sight, and the movements concerned in pecking. So that the consciousness which is effective in guiding future action is an accompaniment of the stimulation of centres that are different from those concerned in the behaviour over which guidance is exercised. And if this interpretation of the observed facts be correct, it supports the conclusions reached from _a priori_ considerations. It seems further to show that, not only is a nervous system necessary for the occurrence of controlled behaviour, but that no little complexity in its intercommunications is essential.