IT CONTEXTS. 



CHAPTEE 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 not reappear — 

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

 ance 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 XII. 



Geographical Distribution. 



Present distribution cannot be accounted for by differences in 

 physical conditions — Importance of barriers — Affinity of the 

 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 Glacial period 

 — Alternate Glacial periods in the north and south .. 129 



CHAPTER XIII. 



Geographical Distribution — continued. 



Distribution of fresh-water productions — On the inhabitants of 

 oceanic islands — Absence of Batrachians and of terrestrial 

 Mammals— 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 



