CONTENTS. Y 



nral lOBtincls of the Cuckoo, Ostrich, and Parasitic Bees— Slave-making Ants — 

 Hive-bee, its cell-making instinct— ChanKCs of In!<linct and Structure not neces- 

 earlly simultaneous— Difllcultics of the Theory of the Natural Selection of In- 

 stincts— Xeuter or Sterile Insects— Summary . . . . PAGE 201 



CHAPTER VIII. 



innuiDisM. 



Distinction between the Sterility of First Crospoe and of Hybrids— Sterility various 

 in Degree, not universal, affected by close Interbreeding, removed by Domesti- 

 cation-Laws goveiTiing the Sterility of Hybrids- Sterility not a special Endow- 

 ment, but incidental on other DilTerenccB, 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 ......... 233 



CHAPTER IX. 



ON TIIK IMrEIlFECTION OF THE GEOLOGICAL KECOP.D. 



On the Absence oflntcrmediatc Varieties at the Present Day — On the Nature of Ex- 

 tinct Intermediate Varieties ; on their Number— On the Lapse of Time, as in- 

 ferred from the Kjite of Denudation and of Deposition— On the Lapse of Time as 

 estimated by Years- On the Poorness of our Palcontological Collections— on the 

 Denudation of Granitic Areas— On the Interaiittence of Geological Formations — 

 On the Absence of Intermediate Varieties in any one Formation— On the sudden 

 Appearance of Groups of Species— On their sudden Appearance in the lowest 

 known Fossilifcrous Strata— Antiquity of the Habitable Earth . . 2CC 



CHAPTER X. 



ON THE GEOLOGICAL SUCCESSION OF ORCLVXIC BEINGS. 



Ou the Slow and Successive Appearance of New Species— On their Different Rates 

 of Cliange— Species once lost do not reappear — Groups of Species follow the 

 same General Kules in their Appearance and Disappearance as do Single Species 

 — On Extinction— On Simultaneous Changes in the Forms of Life throughout 

 the World— On the Affinities of E.\tinct Species to each other and to Living Spe- 

 cles- On the State of Development of Ancient Forms— On the Succession of the 

 eamc Types within the same Areas— Summary of preceding and present Chapter 



293 



CHAPTER XI. 



GEOGUAmiCAL DISTRIUITION. 



PrcBont Distribntlon cannot bo accounted for by Differences In Physical Conditions 

 — Importance of Carriers — Aflliiity of the Productions of the same Continent— 



