PREFACE 



DURING recent years an enormous advance has been made 

 in the knowledge of cell-phenomena. As cells are the 

 ultimate units of all living matter, the significance of their 

 phenomena in connection with a study of the problems of 

 heredity is obvious. Such information is, however, scattered 

 in a number of scientific journals, and it is difficult for the 

 general biologist to keep up to date. In the present volume 

 I have attempted to apply recent discoveries, as well as 

 experimental work upon cells, to some problems in heredity, 

 and I believe that I have thus arrived at a satisfactory har- 

 monising of the results of the Mendelian experiments with 

 the observations of the Biometricians. This has been done by 

 showing that some parts of the cells involved in fertilisa- 

 tion that is, in the production of a new individual are dis- 

 tributed in an alternative manner, while other parts simply 

 divide in bulk. Correns has suggested that the characters 

 that are inherited according to the Mendelian law are not 

 specific. In 1907 I suggested that there were two classes of 

 characters, which behaved in different manners with regard 

 to inheritance, but I believe that a complete theory, dividing 

 characters into individual and racial, and attributing to each 

 a different ' mode of transmission, is put forward here for the 

 first time. 



To this theory I suggest as a corollary, a fresh hypothesis 

 regarding the problem of sex. 



In every case I have tried to deal impartially with the 

 evidence at my disposal, and have accepted the facts de- 

 monstrated by all parties, while often disagreeing with 



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