And such selection implies intelligence in almost its simplest expression. We may say, therefore, that, whereas instinctive behaviour is prior to individual experience, intelligent behaviour is the outcome and product of such experience. This distinction is presumably clear enough; and it is one that is based on the facts of observation. But we must not fail to notice that, though the logical distinction is quite clear, the acquired modifications of behaviour, which we speak of as intelligent, presuppose congenital modes of response which are guided to finer issues. We may say, then, that where these congenital modes of response take the form of instinctive behaviour, there is supplied a general plan of action which intelligence particularizes in such a manner as to produce accommodation to the conditions of existence. We have already frankly admitted that, in the present state of our knowledge, we do not know with any definiteness how intelligent modification of behaviour is effected. But it seems probable that from all parts of the automatically working organic machine messages come in to the centres of conscious control, and that in accordance with the net result of all these messages, and the past experience which they recall, other messages go out to the automatic centres, and, by checking their action here and enforcing it there, give new direction to the resulting behaviour. If this be so, the consciousness associated with the control-centres is like the person who sits in a central office and guides the working of some organized system in accordance with the information he is constantly receiving; who sends messages to check activity in certain directions and to render it more efficient and vigorous in others. It may be said, however, that intelligent guidance is, at any rate in such simple cases as the selection of a palatable grub and the rejection of a nauseous ladybird, itself determined by instinctive likes and dislikes. All young chicks apparently find wasp-larvæ palatable and ladybirds the reverse; and this is just as much the outcome of heredity as the instinctive act of pecking. Since, therefore, heredity determines what shall be selected and what rejected--since the likes and dislikes are themselves instinctive--any essential difference between congenital and acquired behaviour seems to be evanescent.