CONTENTS. vn 



CHAPTEK VII. 



Miscellaneous Objections to the Theory of Natural 



Selection. 



Longevity — Modifications not necessarily simultaneous — Modifications 

 apparently of no direct service — Progressive development — Characters 

 of small functional importance, the most constant — Supposed incom- 

 petence of natural selection to account for the incipient stages ot 

 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 disbeliev- 

 ing in great and abrupt modifications Page 168-204 



CHAPTEE VIII. 



Instinct. 



Instincts comparable with habits, but different in their origin — Instincts 

 graduated — Aphides and ants — Instincts variable — Domestic in- 

 stincts, their origin — Natural instincts of the cuckoo, molothrus, 

 ostrich, and parasitic bees — Slave-making ants — Hive-bee, its cell- 

 making instinct — Changes of instinct and structure not necessarily 

 simultaneous — Difficulties of the theory of the Natural Selection of 

 instincts — Neuter or sterile insects — Summary .. .. 205-234 



CHAPTEE IX. 



Hybridism. 



Distinction between the sterility of first crosses and of hybrids — Sterility 

 various in degree, not universal, affected by close interbreeding, re- 

 moved by domestication — Laws governing the sterility of hybrids — 

 Sterility not a special endowment, but incidental on other differences, 

 not accumulated by natural selection — Causes of the sterility of first 

 crosses and of hybrids — Parallelism between the effects of changed 

 conditions of life and of crossing — Dimorphism and Trimorphism — 

 Fertility of varieties when crossed and of their mongrel offspring not 

 universal — Hybrids and mongrels compared independently of their 

 fertility — Summary 234-263 



