INTELLIGENCE IN LOWER VERTEBRATES 221 



one of the latter was placed in the compartment of the larger 

 fish. It was treated at first much as before, but after a little 

 " the perch became more demonstrative toward it, but re- 

 strained themselves from striking, so long as it quietly 

 avoided them." When the minnow made a quick movement 

 the perch were more apt to dart after it and on one occa- 

 sion it had to be rescued. After a time the pursuit of the 

 minnows became less eager and although they were followed 

 the instinct to dart at them was generally inhibited. 



The formation of an association in relation to the glass 

 partition was shown by the fact that when the partition was 

 removed the fish behaved much as if it still remained. " The 

 male swam out to the place, stopped, made little bumps 

 forward as if expectng to strike the usual obstruction, and 

 was plainly at a loss. He then turned and swam down as 

 if following the glass." Often the fish would swim to the 

 mark where the plate had been and then turn back. 



These experiments showed that the natural instinct of the 

 perch to charge after the minnow was inhibited, although not 

 completely so, and that the fish came to associate the appear- 

 ance of a certain region of the aquarium with the experience 

 of being bumped. Pieron found that a cyprinoid fish, 

 Carassius auratiis, would snap at live worms placed in a glass, 

 tube, but the number of attacks in a given time gradually 

 grew less on the following days. The glass tube was placed 

 in the water for twenty-seven minutes each time. In the 

 first experiment the fish made 117 attacks, on the three 

 successive days the attacks were 58, 38, and 25 in number. 

 Several days later the number of attacks had diminished 

 still more. The tube was then left in the aquarium and the 

 fish soon came to ignore it entirely, and even refused to eat 

 the worms when they were placed free in the water. WTien 

 the number of attacks on the tube diminished they could be 



