CONTENTS 



. PAGE 



I. GENERAL SURVEY OF THE LIFE HISTORY IN THE PROTOZOA, WITH " 

 THE QUESTIONS IT RAISES. LIFE, DEATH, REPRODUCTION, 

 MATING, REJUVENESCENCE, "POTENTIAL IMMORTALITY" ... 13 



II. HEREDITY AND VARIATION IN PROTOZOA, IN REPRODUCTION FROM 

 A SINGLE PARENT. "THE INHERITANCE OF ACQUIRED CHARAO-' 

 TERS." THE EXISTENCE OF MANY DIVERSE STOCKS IN A SINGLE 

 SPECIES. CONSTANCY OF THE STOCKS. "PURE LINE INHERIT- 

 ANCE" AND THE RESULTS OF SELECTION. DIFFICULTIES FOR THE 

 THEORY OF EVOLUTION 38 



III. RESULTS OF INTENSE AND LONG CONTINUED STUDY OF CHANGES 

 IN A STOCK. INHERITED VARIATIONS IN THE PURE RACE. VISIBLE 

 EVOLUTION 67 



IV. CAN WE EXPERIMENTALLY CHANGE THE HEREDITARY CHARAC- 

 TERS? HEREDITY OF ENVIRONMENTAL EFFECTS. HEREDITY AND 

 VARIATION IN BACTERIA AND SIMILAR .ORGANISMS .... 85 



V. THE NATURAL HISTORY OF MATING. SEX, ITS NATURE AND CON- 

 SEQUENCES. SEX IN THE PROTOZOA. Is SEX COEXTENSIVE WITH 

 LIFE AND NECESSARY TO ITS CONTINUANCE? 106 



VI. WHAT ARE THE RESULTS OF MATING? REJUVENESCENCE AND 



MATING. HEREDITY AND VARIATION, AND MATING .... 141 



VII. How DOES MATING BRING ABOUT BOTH BIPARENTAL INHERIT- 

 ANCE, AND DIVERSITY IN HEREDITARY CHARACTERS? WHAT 

 EFFECT HAS MATING ON THE STOCK AS A WHOLE? DOES IT 

 INCREASE VARIATION? DOES IT DECREASE VARIATION? WHAT 

 Is ITS RELATION TO EVOLUTION? 170 



VIII. COMPARISON OF THE GENETIC PHENOMENA IN THE PROTOZOA WITH 

 THOSE IN HIGHER ORGANISMS. GENERAL VIEW OF DEVELOP- 

 MENT, MATING AND EVOLUTION 198 



