MUNTAL POWERS. 85 



a certain amount of reason. No doubt it is often difficult 

 to distinguish between the power of reason and that of in- 

 stinct. For instance, Dr. Hayes, in his work on "The 

 Open Polar Sea," repeatedly remarks that his dogs, instead 

 of continuing to draw the sledges in a compact body, 

 diverged and separated when they came to thin ice, so that 

 their weight might be more evenly distributed. This was 

 often the first warning which the travelers received that the 

 ice was becoming thin and dangerous. Now, did the dogs 

 act thus from the experience of each individual, or from 

 the example of the older and wiser dogs, or from an inher- 

 ited habit, that is, from instinct? This instinct may pos- 

 sibly have arisen since the time, long ago, when dogs were 

 first employed by the natives in drawing their sledges; or 

 the Arctic wolves, the parent-stock of the Esquimau dog, 

 may have acquired an instinct impelling them not to attack 

 their prey in a close pack, when on thin ice. 



We can only judge by the circumstances under which 

 actions are performed, whether they are due to instinct, or 

 to reason, or to the mere association of ideas; this latter 

 principle, however, is intimately connected with reason. A 

 curious case has been given by Prof. Mobius,* of a pike, 

 separated by a plate of glass from an adjoining aquarium 

 stocked with fish, and who often dashed himself with such 

 violence against the glass in trying to catch the other fishes, 

 that lie was sometimes completely stunned. The pike went 

 on thus for three months, but at last learned caution, and 

 (eased to do so. The plate of glass was then removed, but 

 the pike would not attack these particular fishes, though he 

 would devour others which were afterward introduced j so 

 strongly was the idea of a violent shock associated in his 

 feeble mind with the attempt on his former neighbors. If 

 a savage, who had never seen a large plate-glass window, 

 were to dash himself even once against it, he would for a 

 long time afterward associate a shock w r ith a window-frame; 

 but, very differently from the pike, he would probably 

 reflect on the nature of the impediment, and be cautious 

 under analogous circumstances. Now with monkeys, as we 

 shall presently see, a painful or merely a disagreeable 

 impression, from an action once performed, is sometimes 

 sufficient to prevent the animal from repeating it. If we 



* "Pie Bewegungen der Thiere," etc., 1873, p. 11. 



