XX TABLE OF CONTENTS 



PAGE 



Answer to the First Difficulty 591 



Answer to the Second Difficulty: Organs of Extreme Perfection 

 and Complication 591 



Darwin's Summary of His Answer to the Third Difficulty, That 

 of Accounting for the Acquisition and Modification of In- 

 stincts through Natural Selection 595 



Darwin's Summary of His Answer to the Difficulty as to the In- 

 ability of Natural Selection to Account for the Fact That Spe- 

 cies When Crossed Are Sterile or Produce Sterile Offspring, 

 Whereas When Varieties Are Crossed Their Fertility is Unim- 

 paired 596 



Bibliography 599 



Glossary 602 



Index 611 



