2l6 DARWINISM AND THE PROBLEMS OF LIFE 



that the fly constantly returns to the same spot, although 

 it has barely escaped from the hand of the catcher 

 a number of times. The fly is certainly not an 

 intelligent animal, otherwise it would know that the 

 spot was dangerous. Clearly, in its flight we have an 

 instinct that causes the animal to fly away quickly, by a 

 sort of reflex action, when a body approaches it rapidly ; 

 an instinct that was not initiated by intelligence, nor 

 practised. 



We must equally discard the Lamarckian principle 

 as an explanatory factor in dealing with the instincts 

 that accompany protective colouring. The murderous 

 mantis, which is of a green colour like the surrounding 

 grass, steals very slowly on its prey. The xylina, that 

 looks like a piece of wood, shams death ; that is to say, 

 remains quite motionless, and finds excellent protection 

 in this way. Can these animals know that their 

 colour is only useful to them if they act in accordance 

 with it ? 



Butterflies that are not eaten on account of a nauseous 

 taste or smell are distinguished, as we saw, by glaring 

 colours. They fly slowly, because it is best for them 

 to be seen clearly, so as to be recognised from afar as 

 inedible before a bird can seize them. No one, surely, 

 will suppose that these animals are conscious of the 

 advantage they have in flying slowly. 



There are, nevertheless, intelligent tracheates whose 

 instincts might seem to have been originally acts of 

 intelligence, which they have improved by reflection, 

 and have transmitted the results to offspring. I refer, 

 especially, to the spiders. 



