18 DOCTRINE OF EVOLUTION 



plies of oxygen, and the waste substances of various 

 kinds. All of these four systems are concerned with 

 *' commissary " problems, so to speak, which every in- 

 dividual must solve for and by itself. 



Another group of systems is concerned with wider rela- 

 tions of the individual and its activities. For example, 

 the motor system accomplishes the movements of the 

 various organs within the body, and it also enables the or- 

 ganism to move about ; thus it provides for motion and 

 locomotion. Systems of support, comprising bones or 

 shells, occur in many animals where the other organs are 

 soft or weak. Perhaps the most interesting of the in- 

 dividual systems of relation is the nervous system. 

 The strands of its nerve fibers and its groups of cells 

 keep the various organs of the body properly coor- 

 dinated, whereas in the second place, through the 

 sensitive structures at the surface of the body, they 

 receive the impressions from the outside world and so 

 enable the organism to relate itself properly to its en- 

 vironment. The last organic system differs from the 

 other seven in that the performance of its task is of 

 far less importance to the individual than it is to the 

 race as a whole. It is the reproductive system, with 

 a function that must be always biologically supreme. 

 We can very readily see why this must be so ; it is be- 

 cause nature has no place for a species which permits 

 the performance of any individual function to gain 

 ascendency over the necessary task of perpetuating the 

 kind. Nature does not tolerate race suicide. 



All organisms must perform these eight functions 

 in one way or another. The bacterium, the simplest 

 animal, the lowest plant, the higher plants and animals, 



