The Life of the Spider 



and will describe a logarithmic spiral within 

 it. It is, in a more complicated degree, 

 a variant of Bernouilli's 'Eadem mutata 

 resurge:' the logarithmic conic curve becomes 

 a logarithmic plane curve. 



A similar geometry is found in the other 

 shells with elongated cones, Turritellae, 

 Spindle-shells, Cerithia, as well as in the shells 

 with flattened cones, Trochidae, Turbines. 

 The spherical shells, those whirled into a 

 volute, are no exception to this rule. All, 

 down to the common Snail-shell, are con- 

 structed according to logarithmic laws. The 

 famous spiral of the geometers is the general 

 plan followed by the Mollusc rolling its stone 

 sheath. 



Where do these glairy creatures pick up 

 this science? We are told that the Mollusc 

 derives from the Worm. One day, the 

 Worm, rendered frisky by the sun, emanci- 

 pated itself, brandished its tail and twisted it 

 into a corkscrew for sheer glee. There and 

 then the plan of the future spiral shell was 

 discovered. 



This is what is taught quite seriously, in 

 these days, as the very last word in scientific 

 progress. It remains to be seen up to what 

 392 



