8 CORA D. REEVES 



Food may be supplied to the fish from the food-bar (// 

 in fig. 2) weighted at one end and pivoted at its center. 

 After food has been placed at both ends, the bar is brought 

 into a horizontal position and held there by an electro- 

 magnet {K in fig. 2). When a fish approaches the patch 

 of light before which he is to be fed, the bar is released by 

 opening a switch. The bar is then free and turns on its 

 pivot until its weighted end is beneath the water in front 

 of the stimulus plate where the fish can secure the food. 



The aquarium is supported on a low table and supplied 

 with running, filtered water. To exclude extraneous light 

 and secure uniform illumination of the apparatus during 

 experimentation the space about the table is enclosed by 

 black building-paper to form a room 6 ft. by 10 ft. This 

 light-tight room includes a west window with light-tight 

 shades. Suspended from the ceiling directly above the 

 aquarium is a 40 watt tungsten lamp at a distance of 157 

 cm. from the water. This lamp is enclosed in a cylindrical 

 metal shade 145 cm. high. As the diameter of the shade 

 is 14 cm. the light is reduced, being only that passing out 

 from its open lower end. To give the fish an environment 

 of more nearly normal color and to keep them from seeing 

 the experimenter, the aquarium table is surrounded by 

 a curtain of yellow cheese-cloth hung from the ceiling 

 within the light-tight room. A cord attached to the slid- 

 ing door {D fig. 2), in partition A, runs straight up to an 

 eye in the ceiling and ends outside the curtain. A counter 

 weight on this door-cord enables the operator to leave the 

 door open at any height. The switch for control of the 

 food-bar magnets is also located outside the curtain. 



2. General Method o." Procedure 



Before an experiment is begun, the window shades are 

 lowered and the ceiling light is turned on, so that the fish 

 may become accustomed to the light and their eyes adapted 

 to the conditions of illumination maintained during the 

 experiment. After half an hour or more all of the fish 

 in the aquarium are shut into the retention compartment 

 (3 in figs. 1, 2) by means of the movable partition B. The 

 experimenter then adjusts the illuminating apparatus and 



