CONTENTS. ix 



CHAPTER V. 



AS TO SPECIFIC STABILITY. 



What is meant by the phrase " sjjeciiic stability;" such stability to be 

 expected a 2^''iori, or else considerable changes at once. — Increasing 

 difficulty of intensifying race characters ; alleged causes of this pheno- 

 menon ; probabl}' an internal cause co-oj)erates. — 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 some- 

 where. ^Gninea-pigs. — Summary and conclusion . . . Parjc 127 



CHAPTEi; vr. 



SPECIES AND TIME. 



Two relations of species to time. — Xo evidence of past existence of minutely 

 gi'aduated intermediate forms when such might be expected a j^^'^*^^^- ~ 

 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 "Wm. Thom- 

 son's views. — Probable period required for ultimate specific evolution 

 from ])rimitive ancestral forms. — Geometrical increase of time required 

 for rapidly multiplying increase of structural difterences. — Proboscis 

 monkey. — Time rci^uired for deposition of strata necessary for Dar- 

 winian evolution. — High organization of Silurian forms of life. — 

 Absence of fossils in oldest rocks. — Summary and conclusion. 



Page 145 



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 



