THE SCAFFOLDING LEFT IN THE BODY. b7 



exceedingly economical, and could not throw all this 

 mechanism away. In fact, Nature almost never parts 

 with any structure she has once made. What she 

 does is to change it into something else. Conversely, 

 Nature seldom makes anything new; her method 

 of creation is to adapt something old. Now, when 

 Nature had done with the old breathing-apparatus, 

 she proceeded to adapt it for a new and important 

 purpose. She saw that if water could pass through 

 a hole in the neck, air could pass through likewise. 

 But it was no longer necessary that air should pass 

 through for purposes of breathing, for that was 

 already provided for by the mouth. Was there any 

 other purpose for which it was desirable that air 

 should enter the body ? There was, and a very subtle 

 one. For hearing. Sound is the result of a wave- 

 motion conducted by many things, but in a special 

 way by air. To leave holes in the head was to let 

 sound into the head. The mouth might have done for 

 this, but the mouth had enough to do as it was, and, 

 moreover, it must often be shut. In the old days, 

 certainly, sound was conveyed to fishes in a dull way 

 without any definite opening. But animals which 

 live in water do not seem to use hearing much, and 

 the sound-waves in fishes are simply conveyed 

 through the walls of the head to the internal ear with- 

 out any definite mechanism. But as soon as land-life 

 began, owing to the changed medium through which 

 sound-waves must now be propagated, and the new 

 uses for sound itself, a more delicate instrument was 

 required. And hence one of the first things attended 

 to as the evolution went on was the construction and 

 improvement of the ear. And this seems to have been 



