xii CONTENTS 



CHAPTER YIII 



PAGE 



Sexual phenomena in multicellular plants The distinction between 

 somatic cells and germ cells Alternation of sexual and asexual 

 generations Suppression of the gametophyte in flowering plants . 95 



CHAPTER IX 



Sexual phenomena in multicellular animals Structure and life history 

 of Hydra and Obelia Alternation of generations The ccelomate 

 type of structure Secondary sexual characters The evolution 

 of sex . , ...... . . . .113 



CHAPTER X 



Origin of the germ cells in multicellular animals Maturation of the 

 germ cells Reduction of the chromosomes Sex determination in 

 insects Different forms of gametes Mutual attraction of the 

 gametes Fertilization and parthenogenesis . . . . .129 



PAKT III. VAKIATION AND HEREDITY 

 CHAPTER XI 



Variation Meristic and substantive variations Fluctuations and 

 mutations Somatogenic and blastogenic variations Origin of 

 blastogenic variations . . . . . . . . . 148 



CHAPTER XII 



Heredity General observations Darwin's theory of pangenesis and 

 Weismann's theory of the continuity of the germ plasm The 

 . nucleus as the bearer of inheritable characters .... 161 



CHAPTER XIII 



The inheritance of acquired characters and the mnemic theory of 



heredity ............ 176 



CHAPTER XIV 



The Mendelian experiments in hybridization The doctrine of unit 

 characters and the purity of the gametes Galton's law of 

 inheritance . . . . . . . . - . . 194 



PART IV. THE THEORY AND EVIDENCE OP 

 ORGANIC EVOLUTION: ADAPTATION 



CHAPTER XV 



Organic evolution versus special creation Spontaneous generation and 



biogenesis The origin of living things ...... 211 



