28 THE NATURE OF LIFE 



The experimenter is now able to con- 

 trol to an astonishing degree the develop- 

 ment of the organism and the future 

 offers great possibilities in this iSeld of 

 work. We should not lose sight, how- 

 ever, of the fact that this sort of develop- 

 ment is by no means indispensable to the 

 conception of reproduction. In the sim- 

 plest forms, such as the blue-green algae, 

 there is no development in this sense nor 

 is there any fusion of gametes or compli- 

 cated nuclear division. The organism, 

 which is a single cell without a definite 

 nucleus, simply divides into two and 

 each half is at once a new organism like 

 the original cell. In such a case we need 

 only to explain the mechanism of cell 

 division and growth in order to give a 

 physicochemical explanation of repro- 

 duction in its simplest form. 



We must remember that reproduction 

 may be entirely absent. Individual cells, 

 as nerve cells, or entire organisms, such 

 as the resting seed, may serve as exam- 

 ples. In these cases there is no reproduc- 



