What is meant by the phrase "specific stability;" such stability to be expected a priori, or else considerable changes at once.—Rapidly increasing difficulty of intensifying race characters; alleged causes of this phenomenon; probably an internal cause co-operates.—A certain definiteness in variations.—Mr. Darwin admits the principle of specific stability in certain cases of unequal variability.—The goose.—The peacock.—The guinea fowl.—Exceptional causes of variation under domestication.—Alleged tendency to reversion.—Instances.—Sterility of hybrids.—Prepotency of pollen of same species, but of different race.—Mortality in young gallinaceous hybrids.—A bar to intermixture exists somewhere.—Guinea-pigs.—Summary and conclusion ... Page [113]
CHAPTER VI.
SPECIES AND TIME.
Two relations of species to time.—No evidence of past existence of minutely intermediate forms when such might be expected a priori.—Bats, Pterodactyles, Dinosauria, and Birds.—Ichthyosauria, Chelonia, and Anoura.—Horse ancestry.—Labyrinthodonts and Trilobites.—Two subdivisions of the second relation of species to time.—Sir William Thomson's views.—Probable period required for ultimate specific evolution from primitive ancestral forms.—-Geometrical increase of time required for rapidly multiplying increase of structural differences.—Proboscis monkey.—Time required for deposition of strata necessary for Darwinian evolution.—High organization of Silurian forms of life.—Absence of fossils in oldest rocks.—Summary and conclusion ... Page [128]
CHAPTER VII.
SPECIES AND SPACE.
The geographical distribution of animals presents difficulties.—These not insurmountable in themselves; harmonize with other difficulties.—Fresh-water fishes.—Forms common to Africa and India; to Africa and
South America; to China and Australia; to North America and China; to New Zealand and South America; to South America and Tasmania; to South America and Australia.—Pleurodont lizards.—Insectivorous mammals.—Similarity of European and South American frogs.—Analogy between European salmon and fishes of New Zealand, &c.—An ancient Antarctic continent probable.—Other modes of accounting for facts of distribution.—Independent origin of closely similar forms.—Conclusion ... Page [144]
CHAPTER VIII.
HOMOLOGIES.