CONTENTS xi 



PAGE 



3. The methods of snails and slugs The protection of 

 plants against their attacks 73 



4. Vegetarian mammals The need for thorough mas- 

 tication 75 



5. Fruit-eating birds 76 



6. Evolution of plants accompanied by increased com- 

 plexity of animal life that depends upon them . . 77 



B. The quest for prey : the supply of food in the sea : 



i. The origin of the carnivorous diet Scarcity of plant 

 life in the open sea At the poles and in deserts Fixed 

 animals not consistent vegetarians Hydroids, Medusae, 

 and anemones are carnivorous The food of star-fish . 78 



2. The demands of active swimming life The food of 

 fish Pre-occupation of the mouth with breathing 

 Rarity of grinders Choice of shrimp and oily food 

 The food of ground fish Dab John Dory Dog-fish . 82 



3. Cuttle-fish Their activity and mode of overcoming 

 prey Their enemy the sperm-whale . . . . . 84 



4. The food of sea-birds 85 



C. The quest for prey : adaptations of land animals : 



1. The stress of land life Land plants abundant but 

 protected against the attacks of animals The chief 

 causes that favour a carnivorous diet . . . . . 87 



2. The food of carnivora Voracious insects Spiders 



and their allies How the web is made .... 89 



CHAPTER VI 



THE BREATH OF LIFE 



Life as a combustion The need for oxygen Our unconscious- 

 ness of daily waste and repair The insufficiency of the 

 metaphor of flame . 99 



The relative abundance of oxygen in water and air at different 



depths Evolution following the quest for oxygen . .103 



Modes of breathing among animals Protozoa, fixed animals, 

 sponges, corals ; the irrigation of. their bodies with water, 

 and the power of pigment in combining with oxygen 

 The respiration in higher animals is carried out by an 

 internal fluid, the blood, which is aerated in the skin cover- 

 ing the gills The adaptation to secure thorough aeration 

 (shells), and greater oxygen-holding capacity of the blood, 



