xiv INTRODUCTION. 



changes is related to consciousness so as to affect 

 it. The next change, so variable in amount, due 

 neither to vibrations nor to sense of sound but to 

 the idea which the sound symbolizes, begins in the 

 mind ; and science does not know how it happens 

 that it is accompanied with change in the brain, of 

 strictly proportionate amount. 



These are undeniable facts, though not what a 

 confiding public has been always taught in science 

 lectures. It may be added that there is no ex- 

 perimental evidence to show whether the amount 

 of nervous change resulting from a given amount 

 of physical stimulus is ever the same after passing 

 through a nervous centre in which it affects con- 

 sciousness as it would be after passing a centre in 

 which it does not. But we have every reason to 

 believe that the reflex actions in which no con- 

 sciousness is involved are strictly proportional to 

 the amount of stimulus ; while we know that when 

 consciousness is affected it will often happen that 

 no obvious action will follow a stimulus which 

 would otherwise be sufficient to produce move- 

 ments. 



In defending the position that the evolutions 

 observable in organization are definite, I have 

 used in the address which follows, few and simple 

 illustrations, but I trust they are sufficient to give 

 stability to the argument. Manifestly the more 

 complex problems of morphology could not have 



