xii ARTICULATE IDEAS 301 



now available, we ask what is the conclusion pointed 

 to with the greatest probability, it is, that on their own 

 lines, and in their own way, some at least of the more 

 intelligent mammals have powers equivalent to those of 

 the ape. 



Intelligence, we shall recognise, develops in different 

 forms, and in divers directions. It originates within the 

 sphere of instinct, and in its earlier stages is shaped by 

 the instinct which it subserves and expands. We must not 

 expect to find dog intelligence to be quite the same thing 

 as cat intelligence or ape intelligence. It is not only a 

 question of difference in degree, but also, in a sense, of 

 difference in quality, arising from difference in origin. 

 Among men, we know that A, who is clever at languages, 

 is incredibly stupid at mathematics, while with B, it is just 

 the opposite. So, a dog may show not merely a highly 

 developed hunting instinct, but real cleverness in the 

 adaptation of past experiences, when it is a question of 

 catching a hare, but he may be also an intolerable dullard 

 about opening a box. 1 



1 We must guard against the assumption that every novel adaptation 

 to special circumstances implies a knowledge of means and ends. What 

 looks ingenious and original may involve only a slight variation of 

 pre-existing impulse in response to a unique stimulus. E.g., Dahl ob- 

 served a spider, which habitually cut the thread holding its fly when 

 carrying the fly off to the hole, fighting with another spider over a 

 prey which was claimed by both. Both spiders were fastened by threads 

 to their own point of support, and the first spider won the victory by 

 severing the thread of the other. If this was not merely a happy blunder, 

 we may regard it as a modified application of a habitual impulse. The 

 rival spider's thread occupied the place ordinarily taken by the meshes 

 entangling the fly, and being so far similar, awakes the cutting impulse. 



Perhaps a similar explanation may be applied to the action of a 

 caterpillar which tried to mount three different sides of a pit in succes- 

 sion (Weir, Dawn of Reason, p. 206). Here, and in a somewhat similar 

 application of the method of exhaustions by a snail (Romanes, p. 26), we 

 shall probably find the key in the habitual moving of the head for pur- 

 poses of exploration. The animal is accustomed to try different directions 

 in succession and adapts the habit very neatly to its special difficulty. 



In some cases selective modification may be at work. Thus an octopus, 

 having been stung by the anemones with which hermit-crabs arm 

 their shells (with an eye to this very result) will cease to seize the shells 

 but will feel inside them instead, and draw the victim out with its 

 tentacles. The same impulse is at work, and its first line of discharge 

 being blocked, it finds another. But it is, of course, possible that the 

 action belongs to the higher type. 



The beetle seen by Mr. Lloyd Morgan (Animal Life and Intelligence, 



