CONTENTS. 



INTRODUCTION. 



SECT. PAGE 



1. The Study of Variation 1 



2. Alternative Methods 6 



3. Continuity or Discontinuity of Variation 13 



4. Symmetry and Meristic Repetition . 17 



5. Meristic Variation and Substantive Variation 22 



6. Meristic Repetition and Homology ....... 28 



7. Meristic Repetition and Division 33 



8. Discontinuity in Substantive Variation : Size 36 



9. Discontinuity in Substantive Variation : Colour and Colour-Patterns . 42 



10. Discontinuity in Substantive Variation : Miscellaneous Examples . 54 



11. Discontinuity in Meristic Variation : Examples ..... 60 



12. Parallel between Discontinuity of Sex and Discontinuity in Variation . 66 



13. Suggestions as to the nature of Discontinuity in Variation ... 68 



14. Some current conceptions of Biology in view of the Facts of Variation 75 



1. Heredity. 2. Reversion. 3. Causes of Variation. 4. The 

 Variability of "useless" Structures. 5. Adaptation. 6. Natural 

 Selection. 



PART I. 



MERISTIC VARIATION. 



Linear Series 87422 



Radial Series 423447 



Bilateral Series 448473 



Secondary Symmetry and Duplicity . . 474 566 



CHAPTER I. ARRANGEMENT OF EVIDENCE 83 



CHAPTER II. SEGMENTS OF ARTHROPODA 91 



