PREFACE TO FIFTH EDITION 



Since the last edition of this little book was pub- 

 lished in 1 91 2 the most noteworthy contribution to 

 o-enetical studies has come from the American 



o 



school. In the fruit - fly, Drosophila, they have 

 found unusually favourable material with which to 

 work, and they have exploited the advantages it 

 offers with energy and acumen. Their object has 

 been to connect the phenomena of heredity with 

 the visible material basis of the chromosomes of the 

 living cell. Indeed, Professor Morgan has declared 

 that, as the result of these researches, the problem 

 of heredity has been solved. While admitting the 

 very high value and interest of the work I am not 

 prepared to subscribe to this dictum. I have tried, 

 however, to present the position of the supporters 

 of the chromosome theory, in order that those who 

 wish to may make themselves acquainted with what 

 is, at the present moment, the most keenly discussed 

 question in heredity. This has necessitated the 



