140 ESSAYS OF A BIOLOGIST 



may merely affect the ducts and apertures of the re- 

 productive system, and be more or less mechanical; 

 or they may concern the use of these systems, in the 

 form of still mechanical instincts, or they may be 

 concerned in some way or other with the emotional 

 side of the animals, and consist in characters and ac- 

 tions which stimulate the emotions of the other sex, 

 characters which we have termed epigamic. 



It is only in higher groups that these emotion- 

 stimulating sexual characters arise, for only in them 

 has mind reached a sufficient degree of perfection. 

 But even though detailed study reveals in a bird or 

 a mammal a mental life of a complexity far more 

 considerable than the average man would imagine, 

 yet on the whole it is straightforward and its currents 

 run fairly direct from stimulus to fulfilment. 



When we reach man, however, the whole aspect 

 of the matter changes. The change is most marked, 

 naturally, in his mental organization. Through his 

 powers of rapid and unlimited association, any one 

 part of his experience can be combined with any 

 other; through his powers of generalizing and of giv- 

 ing names to things, his experience is far more highly 

 organized than that of any animal; through speech 

 and writing he is inheritor of a continuous tradition 

 which enormously enlarges his range of experience. 

 Again, he can frame a purpose and thus put the ob- 

 jective of his actions far further into the future than 

 can lower organisms. 



There are, however, also changes of considerable 



