vii ASSIMILATION AND READJUSTMENT 117 



again later in the day, or perhaps he would make a move- 

 ment to try it, and then, as we should say of a human 

 being, recollect himself. More marked cases of this gradual 

 growth and equally gradual obliteration of the effects of 

 experience may be seen in other animals. Thus Dahl 1 

 gave a spider a fly dipped in turpentine. The spider 

 sprang upon it three times, and, disliking the turpentine, 

 withdrew on each occasion. After the third attempt it 

 turned aside when the fly came in sight. Three instances 

 sufficed to inhibit the impulse to spring. Nor would the 

 spider for some hours attack a fly of the same species that 

 was innocent of turpentine. The next day the spider 

 attacked the fly in turpentine again, but once only. 



Here three experiences were necessary to establish the 

 result in the first instance, and on the following day the 

 effect was partially obliterated, so that one instance was 

 needed to renew it. Every one is familiar with similar 

 points in the working of human memory the " fixing " of 

 a verse by repetition, its fading with time, and its revival 

 by perhaps a single reading. 



It may be worth while to place in contrast with the in- 

 stances given above a case of extreme stupidity in this 

 respect. Speaking of a number of fish in an aquarium, 

 Mr. Bateson says : 



" None of the fish seem to get any lasting appreciation of the 

 nature of the plate glass wall of the tank. The same fish will 

 again and again knock its head against the glass in trying to 

 seize objects moving on the other side." 



A dangling button, or even a curl of smoke, may attract 

 them. After repeated attempts they will desist, but some 

 of the oldest inhabitants, which have been living in the 

 aquarium about a year, will try again next time. This 

 failure is no doubt partly due to dullness of sense per- 

 ception, but, considering the length of time allowed for 

 learning, it implies a surprising incapacity for turning ex- 

 periences to account a stupidity surpassing even that of 

 Mobius's pike, which, after dashing itself for three months 

 against a glass partition in the attempt to get at some 

 minnows, became at last so firmly persuaded of the danger 

 1 Op. tit. p. 173. 



