PREFACE 



From ancient times heredity has been looked upon 

 as one of the central problems of biological philoso- 

 phy. It is true that this interest was largely specu- 

 lative rather than empirical. But since Mendel's 

 discovery of the fundamental law of heredity in 

 1 865, o r rather since its re-discovery in 1900, a curious 

 situation has begun to develop. 'Thestudents of 

 heredity calling themselves geneticists have begun 

 to draw away from the traditional fields of zoology 

 and botany, and have concentrated their attention 

 on the study of Mendel's principles and their later 

 developments. The results of these investigators 

 appear largely in special journals. Their terminology 

 is often regarded by other zoologists as something 

 bart)arous, — outside the ordinary routine of their pro- 

 fession. The tendency is to regard genetics as a sub- 

 ject for specialists instead of an all-important theme of 

 zoology and botany. No doubt this is but a passing 

 phase; for biologists can little afford to hand over to 

 a special group of investigators a part of their field 

 that is and always will be of vital import. It would 

 be as unfortunate for all biologists to remain ignorant 

 of the modern advances in the study of heredity as 

 it would be for the geneticists to remain unconcerned 



vii 



