BEHAVIOR OF AMPHIPODS WITH RESPECT TO LIGHT. 215 



namely with Gammarus fresh stock, the large majority of re- 

 actions were normal, that is, negative to light intensity and to 

 direction of rays. In this one case of reversed reaction with 

 Gammarus the same animals were used as in Table I., where a 

 reversed reaction is shown. With the tank in position 3 the 

 percentages of normal readings were much higher than is true 

 of the other positions of the tank. This is due to the combined 

 action of intensity and ray direction in position 3, both together 

 forcing more animals to the dark or negative end of the tank 

 than does intensity alone when the tank is in position i. The 

 average percentage is 781^ negative reaction for position 3 of 

 the tank and 663^ for position i. 



In the above three positions of the tank a larger percentage of 

 animals freshly obtained was negative both to light intensity 

 and to direction of rays, in all cases except one series of readings, 

 than were the animals kept in the laboratory for several weeks. 

 Some factor or factors associated with long captivity apparently 

 had an effect in lessening the negative responses of the amphipods 

 to intensity and to direction of rays. Possibly the metabolic 

 rate was depressed by laboratory conditions causing a tendency 

 to a reversal. 



Table II. shows the percentage of experiments giving normal 



Table II. 



Untreated Amphipods. 



Experimental Tank at Right Angles and at Oblique Angles to Direction of Rayi 

 {Positions i, 2 and 3). 



and reversed reactions with all untreated amphipods, both with 

 the tank at right angles and at angles of 45° to the direction of 

 rays. 



