68 THE EVOLUTIONARY THEORY 



which he called biophors and which are combined into 

 groups, named determinants because they are sup- 

 posed to determine the characters of any cell in which 

 they are found. Weismann contended that these 

 biophors assimilate food, grow, and reproduce them- 

 selves by division ; and that the determinants into which 

 they are grouped are engaged in a competitive struggle 

 for food. This struggle eliminates the weaker deter- 

 minants from having part in determining the charac- 

 ters to be transmitted by the germ-cells to offspring. 

 Thus the principle of selection is conceived to operate 

 upon variations within the cell — variations too sHght 

 for observation even by means of a microscope. The 

 fact that this theory represents an effort to solve the 

 important and pressing problem as to how determi- 

 nate variations originate has secured for it more seri- 

 ous attention than its evidence, or lack of evidence, 

 warrants. It is purely conjectural, for it is based upon 

 a description of the internal structure of cells which 

 cannot be verified. If biophors exist, they escape 

 detection by the most powerful microscope. 



The experiments in cross-breeding of an Augustin- 

 ian monk, Gregor Mendel, the results of which were 

 pubhshcd in 1865, but which attracted no particular 

 notice until his facts were rediscovered by de Vries 

 and others in 1899, have thrown important light upon 

 the laws of transmission of characters to offspring. 

 Mendel's law, as it is called, is that the sexual or germ- 

 cells of an organism produced by cross-breeding bear 

 the parental characters thus brought into one organ- 



