CHAPTER VII 



FURTHER OBSERVATIONS ON THE GEOMETRICAL SNARE 



Ultimate fate of temporary spiral Reversal of spiral Reason of reversal 

 of spiral Example of plasticity of instinct Spider's power to esti- 

 mate tension Delicacy of sense of touch Industry of Aranens 

 Mode of emission of filament Economy of spider and destruction of 

 snare Perfection and imperfection in snare. 



IN the previous chapter I have endeavoured to make 

 clear the mathematical powers by which I believe the 

 spider works, and I now pass to consider some other 

 features of interest in the geometry of the circular 

 snare. 



I must first mention one incident in the workmanship 

 of the spider, since it serves to illustrate how a certain 

 step in the architecture can serve merely as a temporary 

 support until the next step is complete. I refer to 

 the ultimate disappearance of the temporary spiral. 

 If the viscid spiral was brought to a completion 

 while the temporary spiral still remained in place, 

 then the final workmanship would consist of a 

 mixture of two spirals, one of viscid and the other 

 of non-viscid lines. But so clumsy an architecture 

 will not suit the spider. It works on a more perfect 

 plan. Its edifice must contain only a single spiral 

 composed solely of viscid lines. How does it effect 

 this? We watch the spider at its work. In the snare 

 under observation the temporary spiral is complete, 

 and we notice that the spider has just sufficient room 



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