xii CONTENTS 



CHAPTER VII 



PAGE 



Progressive and regressive variations Recapitulation Reappearance ol 

 tin- GharadgEhduaanflteJtncertorB Regression in domesticated animals 

 Crosses between natural races Galton's theory of heredity The 

 bulk of characters inherited from remote ancestors The village-sheik 

 Prehistoric human remains Conclusions ..... 109 



CHAPTER VIII 



Causes of variation Amphimixis Not compatible with facts of maturation 

 and fertilisation Elimination of useless variations by bi-parental 

 reproduction Conclusions . . 124 



CHAPTER IX 



Environment as the cause of acquired characters but not of inborn variations 

 Discussion of so-called inherited diseases Cases claimed as proving 

 the transmission of acquired characters Acquired immunity and 

 inborn immunity Brown-S guard's experiments The inheritance 

 of instincts Social bees and ants Effect of illness upon growth 

 Favourable conditions cause degeneration Stringent selection causes 

 improvement The case for the transmission of acquired characters 

 Environment causes selection Lamarck ian explanation of immunity 

 Natural selection of inborn variations is a question of adaptation to 

 the environment Lamarckian explanation of the production of physi- 

 cal characters Inborn variations arise in the germplasin Conclusions 134 



CHAPTER X 



Mendel's discovery Segregation of gametes The extent of the Men- 

 delian experiments Comparison between the results of the Mendelian 

 experimental and the distribution of the chromosomes in fertilisation 

 A suggestion that Mendelian characters are represented by chromo- 

 somes Blended inheritance Exclusive inheritance Participate in- 

 heritance Mendelian phenomena most perfect in self-fertilising plants 

 A suggestion that Mendelian characters are individual variations 

 and that characters which blend arc racial Evidence in support of 

 this theory . . . . 166 



CHAPTER XI 



The function, production, and determination of sex Sex alternating in 

 the same individual Experiments on the determination of sex 

 Wilson's theory of the determination of sex The Mendelian inter- 

 pretation of the determination of sex Archdall Reid's theory that 

 Mendelian characters are non-sexual traits reproduced in the sexual 

 mode A suggested explanation Potentiality of producing secondary 

 sexual characters present in both sexes Sex is a character which 

 is probably transmitted alternatively like individual variations 

 Conclusions ....... . ... 190 



CHAPTER XII 



Some general considerations . . . 212 



BIBLIOGRAPHY 222 



INDEX . 231 



