32 Experience the determining factor 



which the one individual becomes two, he 

 remarks : " In the division the two portions 

 are equal, neither is the older nor the younger. 

 Thus there arises an unending series of in- 

 dividuals, each as old as the species itself, each 

 with the power of living on indefinitely, ever 

 dividing hut never dying^" 



And now, in the next place, "it should 

 also be borne in mind that," as one of 

 Weismann's ablest supporters has observed, 

 "many of these unicellular organisms... are 

 highly differentiated, i.e. [are provided] with 

 great complexity of structure... and that 

 many have very definite and interesting 

 modes of behaviour, such as swimming in 

 a spiral, seeking light or avoiding it... trying 

 one kind of behaviour after another — func- 

 tional peculiarities, some of which cannot 

 be described without using psychological 



' Italics mine. 



