PREFACE IX 



Mendelian factors, it would be folly to close one's 

 eyes to so patent a relation. Moreover, as biologists, 

 we are interested in heredity not primarilj^ as a mathe- 

 matical formulation but rather as a problem concern- 

 ing the cell, the egg, and the sperm. 



T. H. M. 



\ 



PREFACE TO SECOND EDITION 



We have tried to bring the book up to date not 

 only by adding here and there throughout the text 

 the latest results on the subject, but also by adding 

 two entirely new chapters, and new maps of the 

 best known mutant factors. Much new material 

 has been added to the chapter on sex; the chapter 

 on selection has been largely rewritten. The new 

 chapters are one on heredity in Protozoa, and one 

 on mutation in the evening primrose. In the 

 latter field, the latest results of de Vries and others 

 on Oenothera, and the work on balanced lethals, 

 bid fair to bring the earlier discoveries of de Vries 

 into line with more recent work in the whole field 

 of mutation and inheritance. 



In place of the ''A])pendix" we have pre]:)ared a 

 small manual for laboratory use (Henry Holt and 

 Co., Publishers) that gives directions for carrjnng 

 out genetic experiments with the pomace i\y. These 

 experiments have been i)icked out as the ones most 



