CONTENTS 



I. EARTH 1 



n. EVOLUTION 11 



ni. THE PROTOVERTEBRATE 21 



IV. THE KIDNEY 3I 



V. THE ELASMOBRANCHS 53 



VI. THE LUNGFISH 7I 



Vn. THE AMPHIBIA 85 



Vin. THE BONY FISHES IO3 



EX. THE REPTILES AND BIRDS 11/ 



X. THE MAMMALS I3I 



XI. ANIMALS THAT LIVE WITHOUT WATER I47 



xn. MAN 175 



xni. CONSCIOUSNESS 197 



TECHNICAL NOTES AND BIBLIOGRAPHY 227 



INDEX 283 



