PREFACE TO THE REVISED EDITION 



NEARLY ten years have passed since this book first 

 appeared. The biological Rip van Winkle of today 

 who, awaking after a decade of somnolence, gazes again 

 upon the genetic village of Falling Waters, will indeed 

 need to rub his astonished eyes at the changed scene 

 that now spreads out before him. Many old familiar 

 landmarks, such as "unit characters" and "dominance," 

 show signs of dilapidation, while strange children, 

 shouting a medley of outlandish words, "linkage," 

 "tetraploidy," and "non-disjunction," for example, are 

 playing new games on the village green. 



Although the remarkable advances in this field of 

 science are well treated in considerable detail by several 

 recent text-books, notably those of Castle, Morgan, 

 Conklin, and Babcock and Clausen, perhaps there still 

 remains the original need for a more elementary pre- 

 sentation of the salient points of genetics, not only for 

 the interested but confused layman, but also for the 

 initiation of the prospective student who is attracted to 

 the study of heredity. 



To perform this service is the ambitious object of 

 the present revision. 



Three new chapters, XI, XII and XIII, have been 

 added and the whole book has been thoroughly worked 

 over and rearranged. Chapter XIII upon Sex De- 

 termination has practically been written by Professor 

 S. I. Kornhauser of Denison University and the entire 



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