CONTENTS. 



CHAPTEK V. 



AS TO SPECIFIC STABILITY. 



What is meant by tlie phrase "specific stability;" such stability to be 

 expected a priori, or else considerable changes at once. Increasing 

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

 menon ; probably an internal cause co-operates. A certain defmiteness 

 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. Guinea-pigs. Summary and conclusion . . . Page 127 



CHAPTER VI. 

 SPECIES AND TIME. 



Two relations of species to time. No evidence of past existence of minutely 

 graduated 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 Win. Thom- 

 son'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 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 

 insurmoimtable in themselves ; harmonize with other difficulties. 

 Fresh- water fishes. Forms common to Africa and India ; to Africa and 



