CONTENTS 6 



Variation — Compensation and economy of growth — False correlations 

 — Multiple, rudimentary, and lowly organized structures variable — 

 Parts developed in an unusual manner are highly variable: specific 

 characters more variable than generic: secondary sexual characters 

 variable — Species of the same genus vary in an analogous manner — 

 Reversions to long-lost characters — Summary 190 



CHAPTEH VI 



DIFFICULTIES OF THE THEORY 



DiflBculties of the theory of descent with modification — Absence or rarity 

 of transitional varieties — Transitions in habits of life — Diversified habits 

 in the same species — Species with habits widely different from those of 

 their allies — Organs of extreme perfection — Modes of transition — Cases 

 of difficulty — Natura non facit saltum — Organs of small importance — 

 Organs not in all cases absolutely perfect — The law ol Unity of Type 

 and of the Conditions of Existence embraced by the theory of Natural 

 Selection 233 



CHAPTER VII 



MISCELLANEOUS OBJECTIONS TO THE THEORY OF 



NATURAL SELECTION 



Longevity — Modifications not necessarily simultaneous — Modifications ap- 

 parently of no direct service — Progressive development — Characters of 

 small functional importance, the most constant — Supposed incompetence 

 of natural selection to account for the incipient stages of useful struc- 

 tures — Causes which interfere with the acquisition through natural 

 selection of useful structures — Gradations of structure with changed 

 functions — Widely different organs in members of the same class, de- 

 veloped from one and the same source — Reasons for disbelieving in 

 great and abrupt modifications . . . , .... 288 



