180 ANIMAL BEHAVIOUR 



facts: (i) The movements of one animalcule are often quite 

 different from those of another, even in the same medium: 

 so soon is the note of individuality struck. (2) The restless 

 roving is not at random, and when food is scarce it is in- 

 tensified, passing insensibly into ' hunting '. (3) Many of 

 the simplest animals exhibit quite definite reactions to stim- 

 uli. They respond by particular movements to changes in 

 temperature, in illumination, and in the chemical composition 

 of the medium. As there is no nervous system, but simply 

 a specific inborn protoplasmic organisation, we may use the 

 phrase unicellular organic reaction for what is in a far-off 

 way comparable to the reflex action of a higher animal. 



The adherents of the mechanistic school point out that the 

 Amoeba is a reservoir of energy which is tapped by various 

 stimuli such as the freshness of the water, the chemical 

 composition, the temperature, and the illumination. Its 

 locomotion represents the natural outflow of the stored en- 

 ergy, and the direction of its journeying depends on the con- 

 tinually varying stimuli with which it meets. But when we 

 really study the Amoeba, as Professor Jennings (1906) has 

 done, the possibility of any simple description of its doings 

 disappears. Its general condition has much to do with its 

 reactions; the direction of movement is not wholly deter- 

 mined by the position of the stimulus or the part of the body 

 on which it acts; the moving Amoeba shows in its transient 

 differentiation a trafficking with time; what it has done is 

 an important factor in determining what it will do; the 

 types of reaction are not stereotyped ; it is not possible to 

 predict the movements from a knowledge of the direct re- 

 sults of the external influence. So the life of the Amoeba 

 is not such a simple affair as some would make out. We 

 require a kind of description different from that which 



