1 8 INTRODUCTION 



constructing the fabric of Evolution, one of these 

 has been taken, the other left. 



Partly because of the limitations of its purely- 

 physical name, and partly because it has never 

 been worked out as an evolutionary force, the 

 function of Reproduction will require to be intro- 

 duced to the reader in some detail. But to realize 

 its importance or even to understand it, it will be 

 necessary to recall to our minds the supreme place 

 which function generally holds in the economy of 

 life. 



Life to an animal or to a Man is not a random 

 series of efforts. Its course is set as rigidly as 

 the courses of the stars. All its movements and 

 changes, its apparent deflections and perturbations 

 are guided by unalterable purposes ; its energies 

 and caprices definitely controlled. What con- 

 trols it are its functions. These and these only 

 determine life ; living out these is life. Trace back 

 any one, or all, of the countless activities of an 

 animal's life, and it will be found that they are 

 at bottom connected with one or other of the 

 two great functions which manifest themselves in 

 protoplasm. Take any organ of the body — 

 hand or foot, eye or ear, heart or lung — or any 

 tissue of the body — muscle or nerve, bone or 

 cartilage — and it will be found to be connected 



