CONTENTS 



INTRODUCTION 



PAGE 



3 



PART I. GENETICS 



I. Darwin's Theory of Evolution and its Evidences 7 

 II. Contributions of Lamarck, Weismann, and Herbert 

 Spencer to the Theory of Evolution; Darwin's 



Theory of Pangenesis 18 



[II. Are Acquired Characters Inherited ? 28 



IV. Weismann's Theory of Heredity 47 



V. Attempts to Classify and Measure Variation : Biom- 

 etry 55 



\J. The Mutation Theory 71 



VII. The Pioneer Pl.\nt Hybridizers : the Discovery and 



Redt scovery of Mendel's. Law 82 



VIII. Mendel's Law of Heredity Illustrated in Animal 



Breeding 88 



IX. Some Mendelian Terms and their Uses 98 



"■ "X. Calcul.\ting INIendelian Expectations 104 



XI. Modified Mendelian Ratios; Heterozygous Char- 

 acters; Atavism or Reversion 109 



XII. The Unit-Characters of Rodents VZ'ia 



XIII. Unit-Characters in Cattle and Horses 130 



XIV. Unit-Characters in SwaNE, Sheep, Dogs and Cats 137 

 XV. Unit-Characters in Poultry and in Plants . . . 145 



XVI. Unit-Characters of Insects 154 



XVII. Sex-Linked and other Kinds of Linked Inheritance 



IN Drosophila 159 



XVIII. Drosophila Type and Poultry Type of Sex-Linked 



Inheritance 164 



— ^XIX. Linkage 167 



XX. The Nature of Genes 177 



XXI. Are Unit-Characters (Genes) Constant OR Variable? 182 

 XXII. Inheritance OF Size and other Quantitative Char- 

 acters. The Hypothesis of Multiple Factors 190 



"^ XXIII. Genetic Changes and the Chromosomes 205 



XXIV. Genetic Changes in Asexual Reproduction, in Par- 

 thenogenesis, AND IN Self-Fertilization . . . 209 



vii 



