HEREDITY AND EVOLUTION 99 



stituents? This question has not yet been an- 

 swered with certainty. The cell-system forms 

 an enormously complex moving equihbrium, 

 which must in one way be regarded as a single 

 and indivisible unit. From this point, of view it 

 may justly be maintained that the basis of hered- 

 ity and of the vital activities generally is repre- 

 sented by the cell-system in its totality. But 

 such a position, philosophically correct though it 

 may be, cuts us off from the possibilities of exact 

 analysis. We have every right to inquire in what 

 way the energies of cell-life are distributed in the 

 system and how they are related; and the ques- 

 tion whether certain elements of the system may 

 possess an especial and primary significance for 

 the determination of the cell-activities forms a 

 legitimate part of this inquiry. 



I stand with those who have followed Oscar 

 Hertwig and Strasburger in assigning a special 

 significance to the nucleus in heredity, and who 

 have recognized in the chromatin a substance that 

 may in a certain sense be regarded as the idio- 

 plasm. This view is based upon no single or 

 demonstrative proof. It rests upon circumstan- 

 tial and cumulative evidence, derived from many 

 sources. The irresistible appeal which it makes 

 to the mind results from the manner in which it 

 brings together under one point of view a multi- 

 tude of facts that otherwise remain disconnected 

 and unintelligible. What arrests the attention 

 -when the facts are broadly viewed is the unmis- 



