14 INTRODUCTION. 



plasm itself. They affect the entire round of life ; they 

 determine the whole morphology of living things ; in a 

 sense they are life. Yet, in constructing the fabric of 

 Evolution, one of these has been taken, the other left. 



Partly because of the limitations of its purely physi- 

 cal name, and partly because it has never been worked 

 out as an evolutionary force, the function of Repro- 

 duction will require to be introduced 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 defi- 

 nitely controlled. What controls 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 either with Nutrition or with 

 Reproduction. Just as everything about an engine, 

 every bolt, bar, valve, crank, lever, wheel, has some- 

 thing to do with the work of that engine, everything 

 about an animal's body has something to do with the 

 work prescribed by those two functions. An animal, 

 or a Man, is a consistent whole, a rational production. 



