What are the stimuli to the actions of a higher organism? It is true that their elements are energies such as we have indicated, but these energies are integrated to form _individualised stimuli_ (Driesch). The stimulus in an experimentally studied taxis is, perhaps, a field of parallel pencils of light rays of definite wave length; but in the action of a man, or a dog say, the stimulus is an immensely complicated disturbance of the ether, producing an _image_ upon the retina of the animal. A sound stimulus employed in an investigation may be the relatively simple atmospheric disturbance produced by the sustained note of a syren or violin-string; but the stimulus in listening to an orchestra may consist of dozens of notes, with all their harmonies, sounding simultaneously at the rate perhaps of some hundred or two in the minute. All these are _integrated_ by the trained listener, and one or two false ones among the multitude may entirely spoil the effect of the execution. Surely there is here something more than a mere difference in degree. More important still is the strict functionality between stimulus and action that the theory of tactic responses imposes on itself. Putting this very precisely (but no more precisely than the theory demands), we say that [Sigma]_A_ = _f_(_x_, _y_, _z_), that is, the series of actions [Sigma]_A_ (the dependent variable) is a mathematical function of the independent variables _x_, _y_, _z_. Now is there anything like this functionality between the acting of the higher animal and the stimulus? Evidently there is not. We recognise someone whom we know very well by any one of a hundred different characters, mannerisms of walk, speech, dress, etc. He or she is the same person, whether seen close at hand, or afar off, or sideways, or in any one of almost infinitely different attitudes, and we respond to each of these very different physical stimuli by the same reaction of recognition: pleasure, dislike, avoidance, greeting, or whatever it may be. To a sportsman shooting wild game the stimulus may be some almost imperceptible tint or shading in cover of some kind, differing so little from its environment as hardly at all to be seen, yet, to his experience, upon this almost infinitesimal variation of stimulus depends his action with all its consequences. In Driesch’s example two polyglot friends met and one says to the other, “My brother is seriously ill,” or “Mon frère est séverèment malade,” or “mein Bruder ist ernstlich erkrankt.” Here the physical stimulus is fundamentally different in each case, but the reaction--the expressions of sympathy and concern, the discussions of mutual arrangements, etc., are absolutely the same. Or let the one friend say to the other, “My mother is seriously ill,” and in spite of the very insignificant difference between the consonantal sound _br_ in this sentence and the corresponding sound _m_ in the other English sentence, the reaction,