CONTENTS XV 



chapter page 



18. Some General Problems of Development 436 



Prefonnation and Epigenesis 436 



Heredity and Enviroment in Development 439 



The Determination of Sex 446 



Problems of Mammalian Development 449 



19. Genetics 456 



The Method of Biometry 457 



The Method of Experimental Breeding 462 



The Method of Cytolog>- 474 



The Method of Experimental Embryology 483 



Genetics in Relation to Evolution 485 



Genetics in Relation to Human Affairs 487 



20. The Theory op Evolution 489 



The Origin of Life 489 



Organic Evolution 494 



The Evidence for Organic Evolution 497 



Human Evolution 528 



21. The Causes of Evolution 539 



The Lamarckian Theory of the Inheritance of Acquired Charac- 

 teristics 539 



The Darwinian Theory of Natural Selection or the Survival of the 



Fittest 544 



The Mutation Theory 557 



Orthogenetic Theories 561 



Isolation as a Cause of Evolution 563 



Evolution by Hybridization 564 



Index 567 



