CONTENTS. vii 



tion — Correlated variation — Compensation and economy of 

 growth — False correlations — Multiple, rudimentary, and lowly 

 organised 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. ,, ., Page 164 



CHAPTER VI. 



Difficulties of the Theory. 



Difficulties 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 of Unity of Type and of 

 the Conditions of Existence embraced by the theory of Natural 

 Selection ., .» „ .» ., 207 



CHAPTER VII. 



Miscellaneous Objections to the Theory of Natural 



Selection. 



Longevity — Modifications not necessarily simultaneous — Modifica- 

 tions apparently 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 structures — 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, 

 developed from one and the same source — Reasons for dis- 

 believing in great and abrupt modifications .. k , ., 262 



