iv CONTENTS. 



CHAPTER XI. 



ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS. 



On the slow and successive appearance of new species — On their 

 different rates of change — Species once lost do no'', reappear — 

 Groups of species follow the same general rules in their ap- 

 pearance and disappearance as do single species — On extinction 

 — On simultaneous changes in the forms of life throughout the 

 world — On the affinities of extinct species to each other and to 

 living species — On the state of development of ancient forms — 

 On the succession of the same types within the same areas — 

 Summary of preceding and present chapter . . Page 89 



CHAPTER Xn. 



GEOGRAPHICAL DISTRIBUTION. 



Present distribution cannot be accounted for by differences ii> 

 physical conditions — Importance of barriers — Affinity of tha 

 productions of the same continent — Centres of creation — Means 

 of dispersal by changes of climate and of the level of the land- 

 and by occasional means — Dispersal during the Grlacial period 

 — Alternate Qlacial periods in the North and South . . 124 



CHAPTER Xm. 

 OEOOBAPHicAL DISTRIBUTION — Continued. 



Distribution of fresh-water productions — On the inhabitants of 

 oceanic islands — Absence of Batrachians and of terrestrial Mam- 

 mals—On the relation of the inhabitants of islands to those of 

 the nearest mainland — On colonisation from the nearest source 

 with subsequent modification — Summary of the last and present 

 chapter 171 



