THE SCAFFOLDING LEFT IN THE BODY iii 



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 pro- 

 vided 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 without any definite mechanism. 

 But as soon as land-life began, owing to the 

 changed medium through which sound-waves must 



