CHAPTER XIII

THE GEOLOGICAL EVIDENCES OF EVOLUTION


What we may expect--The number of known species of extinct
animals--Causes of the imperfection of the geological
record--Geological evidences of
evolution--Shells--Crocodiles--The rhinoceros tribe--The
pedigree of the horse tribe--Development of deer's horns--Brain
development--Local relations of fossil and living animals--Cause
of extinction of large animals--Indications of general progress
in plants and animals--The progressive development of
plants--Possible cause of sudden late appearance of
exogens--Geological distribution of insects--Geological
succession of vertebrata--Concluding remarks



CHAPTER XIV

FUNDAMENTAL PROBLEMS IN RELATION TO VARIATION AND HEREDITY


Fundamental difficulties and objections--Mr. Herbert Spencer's
factors of organic evolution--Disuse and effects of withdrawal
of natural selection--Supposed effects of disuse among wild
animals--Difficulty as to co-adaptation of parts by variation