THE EVOLUTION PROCESS 235 



ology, one peculiarly obvious to the botanist, 

 from the vivid distinctness of flowers and foliage, 

 but denied by none for animals and man as well, 

 is that which treats the functions of living 

 beings as of two main kinds ; grouping on the 

 one side respiration, irritability, and all the 

 other activities of the individual in its self- 

 maintaining life, and then setting over against 

 the whole of these the great function of the 

 species-maintaining life, reproduction. Weis- 

 mann's main work has been to emphasize this 

 distinction, especially from the side of the 

 intimate morphology of the germ-cells; while 

 some of the best chapters of Spencer's " Prin- 

 ciples of Biology " are those in which, after 

 pointing out its intelligibility in terms of the 

 principle of conservation of energy, he elabor- 

 ates the antithesis of nutrition and reproduc- 

 tion by reference to many plant and animal 

 forms. Yet though the principle is one 

 familiar since the dawn of physiology, its 

 applications are still far from exhausted. 

 " While philosophers are disputing over the 

 government of the world, hunger and love are 

 performing the task," says Schiller; and our 

 " Evolution of Sex " is essentially an elabora- 

 tion of one great aspect of this theme. 



APPLICATIONS TOWARDS INTERPRETATION 

 or THE PLANT WORLD. Let us begin with 



