THE YELLOW PERCH 313 



The colors of most fishes are protective in their nature, 

 and the perch is no exception to this general rule. From 

 above, the olivaceous back is with difficulty distinguished 

 from the water itself or the bottom below ; from beneath, the 

 white under parts are colored like the surface of the water 

 or the atmosphere above. The mottled sides also serve to 

 render the perch less conspicuous in an environment of lights 

 and shadows among weeds and rocks on the bottom. It has 

 been noted that in some instances where perch live both in 

 a large lake and in its tributaries, as in Lake Michigan and 

 the rivers which flow into it, the lake fish have a tendency to 

 lighter general coloration and to disappearance of the dark 

 vertical bands. It has been suggested that this difference in 

 color is due, in part at least, to the smaller amount of light, 

 combined with the absence of dark lurking-places. 



The study of the mental organization of the perch is beset 

 with many difficulties, though it is of the greatest interest 

 for the light it may throw on problems connected with the 

 mental life of the higher animals; for the perch is a member 

 of the class of fishes, one of the oldest and most generalized 

 of the vertebrates, to which division man himself belongs. 

 Perch are able to learn, and they profit by experience, even 

 though the line along which education can take place is very 

 narrow. In order to test their capacity to learn, two adult 

 perch were kept in an aquarium in which a glass partition 

 was placed several times a week for a period of about a 

 month. Live minnows were introduced on the opposite side 

 of the partition at the times of experimentation. Of course 

 the perch bumped their noses against the glass in a vain 

 attempt to get at the food temptingly displayed at so short 

 a distance. After they had become accustomed to this reac- 

 tion, whenever they made a movement in the direction of 

 the minnows, the glass partition was removed, and they 

 were watched to see if by their actions they seemed to recall 



