CONTENTS. 7 



ft 



tomal Cause coni)cratoB. — A Certain Dcflnltcnoss In Variations. — Mr. Dar\vin ad- 

 mits the Trlnciplo 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. — Siunmary and Conclusion . . . . . p. 12T 



CHAPTER VI. 



8PE0IES AND TIUE. 



Two Relations of Species to Tlmo. — No Evidence of Past Existence of ^linutely- 

 intermediato Forms when such might be expected a priori.— B&tA, Pterodac- 

 tyls, Dinosauria, and Bbxls.— Ichthyosauria, Chelonia, and Anoura.— Horse An- 

 cestry.— Labyrinthodonts and Trilobitcs.- Two Subdivisions of the Second Rela- 

 tion of Species to Time. — Sir William Thomson's Views. — Probable Period re- 

 quired for Ultimate Speclfio Evolution from Primitive Ancestral Forms.— Geo- 

 metrical Increase of Tlmo required for Rapidly-multiplying Increase of Structural 

 Differences.— Proboscis Monkey.— Time required for Deposition of Strata necea- 

 sary for Dar^vinian Evolution.— High Organization of Silurian Forms of Life.— 

 Absence of Fossils in Oldest Rocks. — Summary and Conclusion . . p. 142 



CHAPTER VII. 



SPECIES AND SPACE. 



The Geographical Distribution of Animals presents Difficulties.— These not insor- 

 mountable 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.— Slmlbrity of European and South 

 American Frogs.- Analogy between European Salmon and Fishes of New Zea- 

 land, etc.— An Ancient Antarctic Continent probable.— Other Modes of accounting 

 for Facts of Distribution.- Independent Origin of Close ly-slmllar Forms.— Con- 

 clusion I'-^'^ 



