However quick this succession of changes may be, there must be an interval of time between the application of the stimulus and the response to that stimulus, hence, the element of time enters into all psychical operations that are not distinctly reflex. Even in the reflexes there is a time element, but it is distinctly shorter than the time interval that enters into the make-up of a conscious psychical operation. This can easily be demonstrated, as has been done, time and again, by actual experiment. "With this gradual dawn of consciousness as revealed to subjective analysis, we should expect some facts of physiology, or of objective analysis, to correspond; and this we do find. For in our own organisms we know that reflex actions are not accompanied by consciousness, although the complexity of the nerve-muscular systems concerned in these actions may be very considerable. Clearly, therefore, it is not mere complexity of ganglionic action that determines consciousness. What, then, is the difference between the mode of operation of the cerebral hemispheres and that of the lower ganglia, which may be taken to correspond with the great subjective distinction between the consciousness which may attend the former and the no-consciousness which is invariably characteristic of the latter? I think that the only difference that can be pointed to is a difference of rate of time."[28] [28] Romanes, _Mental Evolution in Animals_, pp. 72, 73. The gradual cultivation of the senses (evolution), during which the special adaptations of their motor reactions are gradually developed, is a necessary prerequisite to the formation and elaboration of conscious volition.[29] In the foregoing pages I have very briefly discussed this cultivation of the senses and the development of their motor reactions. I have likewise outlined the origin of volition from sensual perceptions; it now becomes necessary in this discussion of mind, in the lower animals, to study those organisms in which volition (choice) first makes its appearance in the shape of conscious determination. [29] Maudsley, _Physiology of Mind_, p. 247. _Stentor polymorphus_ is exceedingly interesting on more than one account. Its queer, trumpet-like shape, with its flaring, bell-like, open mouth (if I may use such a term to indicate its entire cephalic extremity), surmounted by rows of vibratile cilia, its pulsating contractile vesicle, its ability to move from place to place by swimming, are all interesting features; but, when it is ascertained to be the first creature in the entire Animal Kingdom in which a true nervous system is to be found, then it becomes doubly interesting. This protozoan has been a favorite subject for study with microscopists, but Professor Clark of Harvard was the first observer to note and call attention to its nerve-supply. Says he in his note calling attention to this discovery:--