372 THE EVOLUTION THEORY 



cellular organisms may therefore often consist of single biophors, so 

 that in this case the conception of biophors would coincide with that 

 of determinants. In multicellular organisms, on the other hand, 

 I should be inclined on the whole to picture the determinant as 

 a group of biophors, which are bound together by internal forces to 

 form a higher vital unity. This determinant must live as a whole, 

 that is, assimilate, grow, and multiply by division, like every vital unit, 

 and its biophors must be individually variable, so that the separate 

 parts of a cell controlled by them may also be capable of transmissible 

 variation. That they are so, every highly differentiated cell of 

 a higher animal teaches us ; even the smelling-hairs of a crab exhibit 

 a stalk, a terminal knob, and an internal filament, and many muscle-, 

 nerve-, and gland-cells are much more complex in structure. 



