system and its retentiveness 45 



of life are most distinct, is directed and sus- 

 tained by a nervous system. Now to this 

 system belongs in a pre-eminent degree that 

 retentiveness and modifiability which life and 

 experience everywhere imply — characters 

 which we figuratively express by reference 

 to plasticity, as in such terms as protoplasm, 

 idioplasm, germ-plasm and the like. Plas- 

 ticity, in a word, though most pronounced in 

 the higher organisms, where the physiological 

 division of labour has developed a distinct 

 nervous system, is present in all organisms : 

 all alike, though in divers degrees, live and 

 learn. But now a multicellular organism, it 

 is generally allowed, originated in, and still 

 consists of, a colony of unicellular organisms 

 — a colony that has become more of a 

 commonwealth the further its functional 

 division of labour has advanced. It is im- 

 portant then to insist on two points. First, 



