PHENOMENA OF INHERITANCE 261 



These views are not mutually exclusive and it 

 may well be that both are true. We know that 

 germ cells are composed of many parts which 

 differ from one another in both structure and 

 function, and it is highly probable that there 

 are enough of these parts to provide a locus 

 for every inheritance factor. 



There was a time when the cell was the 

 Ultima Thule of biological analysis and when 

 the contents of cells were supposed to be "per- 

 fectly homogeneous, diaphanous, structureless 

 slime." Then the nucleus was discovered 

 within the cell, then the chromosomes within 

 the nucleus, then the chromomeres within the 

 chromosomes, and there is no reason to sup- 

 pose that organization ceases with the powers 

 of our present microscopes. With every im- 

 provement of the microscope and of micro- 

 scopical technique, structures have been found 

 in cells which were undreamed of before, and 

 it is not probable that the end has been reached 

 in this regard. We know that cells contain 

 nuclei and chromosomes and chromomeres, 

 centrosomes and plastosomes and microsomes, 

 and we know that some of these parts differ in 



