VI PREFACE 



In some cases a prediction has been verified, in others 

 an appeal has been successful ; and in regard to some 

 few matters touched on, new views have taken the 

 place of those adopted when my statement was ori- 

 ginally made. I have added notes explanatory of 

 such changes where they are actually necessary. 



E. Ray Lankester. 



December 1889. 



