280 THE PHILOSOPHY OF BIOLOGY 



perpendicularly, and the root must grow downwards 

 because gravity acts along vertical lines. But suppose 

 that reflex actions are tropistic : suppose, for instance, 

 that the moth is bound to fly into the candle flame 

 because the light stimulates both sides of its body 

 equally and this orientates it and guides it towards the 

 direction from which the stimulus proceeds. Complex 

 actions, in the higher animal, on this view are chains 

 of reflexes, and the acting must be unconscious and 

 inevitable, just as the turning of the magnet or green 

 leaf are unconscious movements. Therefore the actions 

 of our fellow-creatures are unconscious and automatic, 

 a conclusion toward which the whole tendency of 

 mechanistic physiology forces us. Yet we know that 

 the conclusion cannot be true. 



Between the obligatory reaction of the compass 

 needle to the magnet, or the analogous heliotropism 

 and geotropism of the plant organism, and the infinitely 

 variable responses of the higher animal toward changes 

 in its environment, consciousness must come into exist- 

 ence. It is absent in the inorganic system and the 

 typical green plant ; it is dim in the sedentary sea- 

 anemone or mollusc ; it becomes brighter in the freely 

 moving Arthropod or fish ; and it is most intense in 

 man. This, it must be admitted, is only a belief, but 

 accepting it as such we may attempt to support it by 

 showing a parallelism of stages of structural complexity 

 and actions. The sensori-motor system is absent in 

 the green plant ; it is simple in the extreme in the sea- 

 anemone ; and it is rudimentary or vestigial in the 

 sedentary mollusc. It becomes more complex in the 

 Arthropod or fish, and it is developed to the greatest 

 degree in ourselves. If we now examine our own 

 mental states, with their corresponding conditions of 

 bodily activity, we see as clearly as possible that our 



