oped, at all events at first, in the neighbourhood of the 

 mouth. Hence the appearance of the tactile papillae and 

 tentacles surrounding the mouth in lower organisms. The 

 repeated stimulation of a part, in other words the function 

 of that part, induces structural changes. Protoplasm being 

 unstable, differentiates along the roads traversed by 

 repeated stimuli. 



Taste also is developed in the same region by the contact 

 of soluble matter. It is a forecast of digestion, and be- 

 comes associated with other organs by means of the nervous 

 mechanism I have described, so that the stimulus of taste 

 issues in the reflex actions of the flow of gastric juice and 

 of swallowing. 



Just as taste is anticipatory to digestion, so the sense <if 

 smell is developed as anticipatory to taste. It is clear that 

 an organism that can so foretaste its prey at a distance will 

 derive a keen advantage in the struggle for existence. 



Sight. — In the oyster we find certain dark-coloured cells 

 which form a rudimentary eye. When an impression falls 

 on this pigmented spot the oyster closes its shell. It is a 

 long step from this simple eye to the eye of the hawk. 

 This bird can discern field-mice and select its victim while 

 hovering out of human sight. Likewise the rudimentary 

 response in the closure of the oyster-shell is incommen- 

 surable with the delicate and swift motion of the bird's 

 wings. There is a long series of developmental changes 

 between the simple ganglion of the oyster and the sight- 

 centres of the bird and their associated centres for the 

 complex muscular movements of its flight. Just as we saw 

 smell to be an anticipatory taste, so we may regard sight 

 as an anticipatory touch, leading to muscular movement. 



We can easily understand how habitual impressions 

 increase in number and complexity; how they come to 

 take different paths, are thus discriminated and issue in 

 increased power and complexity of locomotion. The worm 

 with its pigment cells can only creep ; the insect with its 

 myriad lenses has an incredibly delicate and rapid action 

 of the wing, while blind insects are destitute of wings. 

 And since the mouth is the prominent and alertest part of 

 an animal, the visual organs are also situated near it. 

 Hence also the proximity of an organ sensitive to vibrations 

 of the air — the ear. 



All these organs of sense are connected by sensory nerve- 

 routes with ganglia which are closely associated, and 



