214 The Outline of Science 



for the real food, or vice versa, some of the minnows learned to 

 discriminate infallibly between shadow and substance, both when 

 these were presented alternately and when they were presented 

 simultaneously. This is not far from the dawn of mind. 



In the course of a few lessons, both minnows and sticklebacks 

 learned to associate particular colours with food, and other asso- 

 ciations were also formed. A kind of larva that a minnow could 

 make nothing of after repeated trials was subsequently ignored. 

 The approach of the experimenter or anyone else soon began to 

 serve as a food-signal. There can be no doubt that in the ordi- 

 nary life of fishes there is a process of forming useful associations 

 and suppressing useless responses. Given an inborn repertory 

 of profitable movements that require no training, given the power 

 of forming associations such as those we have illustrated, and 

 given a considerable degree of sensory alertness along certain 

 lines, fishes do not require much more. And in truth they have 

 not got it. Moving with great freedom in three dimensions in a 

 medium that supports them and is very uniform and constant, 

 able in most cases to get plenty of food without fatiguing exer- 

 tions and to dispense with it for considerable periods if it is scarce, 

 multiplying usually in great abundance so that the huge infantile 

 mortality hardly counts, rarely dying a natural death but usually 

 coming with their strength unabated to a violent end, fishes hold 

 their own in the struggle for existence without much in the way 

 of mental endowment. Their brain has more to do with motion 

 than with mentality, and they have remained at a low psychical 

 level. 



Yet just as we should greatly misjudge our own race if we 

 confined our attention to everyday routine, so in our total, as dis- 

 tinguished from our average, estimate of fishes, we must remem- 

 ber the salmon surmounting the falls, the wary trout eluding the 

 angler's skill, the common mud-skipper (Periophthalmus) of 

 many tropical shores which climbs on the rocks and the roots of 

 the mangrove-trees, or actively hunts small shore-animals. We 



