XViii CONTENTS. 



MGS 



CHAPTER XL 



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 

 appearance and disappearance as do single species — On ex- 

 tinction — 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 develop- 

 ment of ancient forms — On the succession of the same types 

 within the same areas — Summary of preceding and present 

 chapter • • 32? 



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 laud, and by occasional means — Dispersal during the 

 Glacial period — Alternate Glacial periods in the north and 

 south 350 



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 cf *he nearest mainland — On colonization from the 

 nearest «ource with subsequent modification — Summary of 

 the las* 'tiid present chapter 380 



CHAPTER XIV. 



MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY- 

 EMBRYOLOGY — RUDIMENTARY ORGANS. 



Classification, groups subordinate to groups — Natural system — 

 Ruies and difficulties in classification, explained on the theory 

 of descent with modification — Classification of varieties — 

 Descent always used in classification — Analogical or adaptive 

 characters — Affinities, general, complex and radiating — Ex- 

 tinction separates and defines groups — Morphology, between 

 members of the same class, between parts of the same indi- 

 vidual — Embryology, laws of, explained by variations not 

 supervening at an early age, and being inherited at a corre- 

 sponding age — Rudimentary organs, their origin explained 

 — Summary ••• • 40* 



