DE VRTE8 AND MENDEL 277 



determinant (which may consist of one or several 

 factors) or by many linked determinants. For 

 those who hold that the transformation of species 

 proceeds not by the modification but by the 

 addition of new or the subtraction of old unit 

 characters (in the above sense) these conclusions, 

 founded on Mendelian research, are of supreme 

 importance in evolution. Professor Bateson has 

 recently prophesied : 



' ... we see Variation shaping itself as a definite, physio- 

 logical event, the addition or omission of one or more definite 

 elements ; and Reversion as that particular addition or 

 subtraction which brings the total of the elements back to 

 something it had been before in the history of the race.' 1 



To those who believe that the outcome of 

 Mendelian research does not bring any essential 

 change in the conception of evolution received 

 from Darwin, the results are still of supreme 

 interest and importance. Just as the splendid 

 cytological work of the past half century helps 

 us to form a picture of the mechanism of fertiliza- 

 tion and of heredity but does not alter our con- 

 ceptions of evolution, so is it with Mendelian 

 research. Upon fertilization and heredity it sheds 

 an even stronger, surer light than that thrown 

 by cytology. We are enabled to understand by 

 the help of examples which obey Mendel's law 

 something of the general, perhaps the universal, 

 mechanism of heredity. This performance and 

 the promise of deeper knowledge in the future 



1 The Methods and Scope of Genetics, Cambridge 1,1908), 48. 



