MIND IN EVOLUTION 511 



it, loses it. Much importance must be attached to simple 

 searchings and probings. As the late Mr. Darbishire put 

 it: " If Necessity was the mother of Invention, Curiosity 

 was almost certainly its father." 



(fe) At an early stage there must have been established 

 a number of particular answers to stimuli, which in the case 

 of Unicellulars may be called organic reactions, keeping the 

 word reflexes for creatures with a nervous system. A good 

 illustration is the answer-back so familiar in the case of 

 the slipper-animalcule, Paramecium. To every hurtful stim- 

 ulation it gives the same answer: it reverses its cilia, it 

 retreats, it twists a little on its axis, it feels its way, and 

 goes full steam ahead often in this way avoiding the ob- 

 noxious stimulus. The capacity of exhibiting this uniform 

 reaction is organised or enregistered in the creature; and 

 these ingrained capacities increase in number. 



(<r) The next step is the ' trial and error ' or perseverance 

 procedure. One reaction is tried after another, till, it may 

 be, one of the movements relieves the creature from stimula- 

 tion. The Stentor reacts in four different ways to the micro- 

 scopic dust which the experimenter showers on it; three an- 

 swers are ineffective, the fourth saves the situation. There 

 is a persisting state of the organism which varies the answers, 

 there is probably a simple expression of conation or en- 

 deavour. 



(d) The main line is continued in such behaviour as is 

 illustrated by multicellular ganglionless animals like star- 

 fishes. There is persistent co-ordination of acts towards a 

 definite result. There is sensori-motor experimentation. 

 Our picture here is that of the brainless starfish persistently 

 disarming the brainless sea-urchin, wrenching off the pedi- 

 cellarise from area after area. This is purposive behaviour, 



