300 Animal Life and Intelligence. 



that our own colour-sensations are probably due to the 

 blending and overlapping in different proportions of three 

 primitive monochromatic bands, but that in all probability 

 in birds the bands are different, and overlapping is largely 

 prevented. Their colour-phenomena must be inconceivably 

 different from ours. And what shall we say of the colour- 

 vision of invertebrates ? Are we justified in supposing that 

 for them, as for us, R, G., and V. are the unstable ex- 

 plosives, and that they are present in the same proportions 

 as with us ? If not, their colour-world cannot be the same 

 as ours. Of the same order it probably is. And all that 

 we can hope to do is to show, as has been shown, that 

 colours which differently affect us affect them also 

 differently. 



In conclusion, we may return to the point from which 

 we set out. The organism is fitted to respond to certain 

 influences of the external world. The organs for the 

 reception of these influences are the sense-organs. When 

 they are stimulated waves of change are transmitted 

 inwards to the great nerve-centres; they are there co- 

 ordinated, and issue thence to muscles or glands. Thus the 

 organism is fitted to respond to the influences from without. 

 The activities of organisms are in response to stimulation. 



We have seen that the cells of the organic tissues are 

 like little packets of explosives, and that the changes which 

 occur in the organism may be likened to their explosion 

 and the setting free of the energy stored up in them. The 

 end-organs of the special senses may be regarded as 

 charged with explosives of extreme sensitiveness. Some 

 are fired by a touch ; the molecular vibrations of sapid or 

 odorous particles explode others ; yet others are fired by 

 the coarser vibrations of sound ; others, once more, by the 

 energy of the sethereal waves. The visual purple is a highly 

 unstable chemical compound of this kind ; expose it for a 

 moment to light, and it topples over to a new molecular 

 arrangement, the colour being at the same time discharged. 

 If the retina has been removed from the body, this is all 



