CONTENTS xi 



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 : 



1. 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, Medusas, 

 and anemones are carnivorous — The food of star-fish . ?8 



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 S4 



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 11REATH 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 ox}'gen 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, 



