14 CONTENTS 



flight. Do birds tire ? The adaptations of the bird-body. 

 Height of the migration-flight. Origin of migratory birds. 

 Their strength, their power of presentiment. Routes of 

 migrating birds. Their memory and sense of direction. 

 Travelling in flocks - 80 



CHAPTER IV.— Reptiles and Amphibia 



Principle of animal-classification. The general properties of 

 animals explained by heredity and adaptation; Darwinian 

 justification of classification. Reptiles and amphibia of 

 former ages. Earlier periods of the earth. How and why 

 the earth has changed up to the present. How the remains 

 of earlier animals have been preserved. Gaps in the 

 remains of extinct animals. Primitive man. Conflicts of 

 extinct animals. Why the gigantic forms of earlier ages 

 became extinct. The death of species. Transformation 

 of species. Why ancient species have been preserved. 

 Why there are still animals of the simplest type. Pre- 

 dominance of a species of animal. Predominance of man. 

 Any variation is possible. Origin of flying animals. Life 

 of our reptiles. Prey. The creeping of serpents. Re- 

 generation, the power to re-form lost members. Its origin 

 by natural selection. Frog-spawn. The skin of amphibia. 

 Repellent and warning colours on nauseous and poisonous 

 animals - 116 



CHAPTER v.— Fishes 



Origin of terrestrial vertebrates and of lungs. Similarities in the 

 Structure of animals. Transformation of organs. Creation 

 or evolution? Many animals are worse than others in 

 this. Selection only creates what is necessary. Atrophy 

 of useless organs. Rudimentary organs in man. Degenera- 

 tion of organs by panmixis. Indifferent characteristics of 

 animals. The differences between species are adaptations. 

 Correlation. Animals that are beyond the range of 

 selection, Qualities and quantities. Explanation of 

 atrophied organs by economy of sustenance and negative 

 selection. Impossible to explain many rudimentary organs. 

 The biogenetic law. Gills in the human embryo. Pre- 

 datory fishes. The rhodeus and the pond-muscle. Senses 

 of fishes, their dangers. History of the eel and the salmon. 

 Artificial selection of fishes - - 150 



