78 E. L. THORNDIKE. 



spectively, the acts done being (i) standing up against the wire 

 netting inclosing the pen, (2) placing the paws on top of a keg, 

 and (3) jumpmg up onto a box. The time intervals were 5 

 seconds in each case. No dog of these ever performed the act 

 before I started to take the meat to feed them, but they did 

 show, by getting up if they were lying down, when the signal 

 was given, or by coming to me if they were in some other part of 

 the pen, that something was suggested to them by it. Why these 

 cases differ from the cases of Cats 3 and 4 ( 10 and 1 2 also pre- 

 sented phenomena like those reported in the cases of 3 and 4) is 

 an interesting though not very important question. The dogs 

 were not kept so hungry as were the cats, and experience had cer- 

 tainly not rendered the particular impulses involved so sensitive, 

 so ready to discharge. Dogs 2 and 3 were older. There is 

 no reason to invoke any qualitative difference in the mental 

 make-up of the animals until more illuminating experiments are 

 made. 



Association by Similarity and the Formation of 



Concepts. 



What there is to say on this subject from the standpoint of 

 my experiments will be best introduced by an account of the 

 experiments themselves. 



Dog I had escaped from AA (o at front) 26 times. He was 

 then put in BB (o at back). Now, whereas 2 and 3, who were 

 put in without previous experience with AA, failed to paw the 

 loop in BB, No. i succeeded. His times were 7.00, .35, 2.05, 

 .40, .32, .10, 1. 10, .38, .10, .05, and from then on he pawed 

 the loop as soon as put in the box. After a day or so he was 

 put inBBi (o at back high). Although the loop was in a new 

 position, his times were only .20, .10, .10, etc. After nine 

 days he was put in a box arranged with a little w^ooden plat- 

 form 2)^ inches square, hung where the loop was inBBi. 

 Although the platform resembled the loop not the least save in 

 position, his times were only .10, .07, .05, etc. 



From the curves given in Figure 19, which tell the history 

 of 10, II and 12 in Bi (o at back) after each had pre- 

 viously been familiarized with A (o at front) , we see this same 



