64 THE PSYCHIC LIFE 



space. The possession of this sense is absolutely in- 

 dispensable to them, for it does not suffice them to 

 know of the presence of an exterior body in order to 

 approach it and seize it; they must furthermore know 

 its position, so as to direct their movements accord- 

 ingly. 



The simplest form of a sense of localization is met 

 with in the Amoeba, which, when it closes about a nu- 

 tritive particle, always emits its pseudopods at pre- 

 cisely that part of its body where the foreign substance 

 caused the irritation. The most complicated instance of 

 localization is met with in the Didinimn, which we have 

 so often cited; the Didinitim knows precisely the po- 

 sition of the prey it follows, for it takes aim at the ob- 

 ject of its pursuit like a marksman, and transpierces it 

 with its nettle-like darts. Between thesp two species, 

 we find all the intermediate instances of a localization 

 of perceptions. 



However, doubts exist upon the question as to 

 whether Proto-organisms knov/ the direction and dis- 

 tance of external bodies, or whether they only succeed 

 in getting at them after a series of tentative move- 

 ments. The observations which we have collated do 

 not solve the question. 



4. ^l/('/()/-_r phase. — We now pass to the motory 

 phase. The movements made by Micro-organisms as. 

 if in response to an excitation, are not in most in- 

 stances simple reflex motions; they are movements 

 adapted to an end. We cannot repeat it too much: 

 these movements are not explained by the simple phe- 

 nomenon of cellular irritabilitj'. 



In the very first instance, they vary according to 

 the excitation; a given excitation produces a corre- 

 sponding motory response; a body situated at the right 



