LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 



Fig. 1 

 Ground plan of the Experiment Aquarium. 

 \. Stimulus compartment. /' and /" recess for stimulus plate. 



2. Discrimination Compartment. 



3. Retention Compartment. 



A and B movable partitions; C fixed partition; D sliding door in partition A; 

 efgh indicate the positions of the corners of a frame above this end of the aquarium; 

 xy plane of section shown in figure 4; 2iv plane of section shown in figure 5. 



lifted in figure 2. A vertical fixed partition, C, divides 

 one end of the stimulus compartment, 1, into two sub- 

 compartments, 1' and 1". Lengthwise of each of the sub- 

 compartments, 1' and 1", extends a plate of opal ground 

 glass set across it so as to form an angle of 45° with the 

 floor and with the end wall. These plates are illuminated 

 from above by patches of white or colored light, and from 

 them this light is diffused into compartment 1. When 

 the sliding door {D in fig. 2) is lifted, a fish in the discrim- 

 ination compartment, 3, has before it a patch of light upon 

 each of the white stimulus plates (5 in fig. 2). If the patches, 

 are unlike in either intensity or wave-length, its instinc- 

 tive behavior toward them may for a time be differential. 



