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HARRY BEAL TORREY AND GRACE P. HAYS 



instance, at 70 cm. from the organism the light used possessed 

 an angular diameter of 4°; at 36 cm., 7°; at 50 cm., 6°; at 

 15 cm., 16°. 



I. A 25 w. tungsten bulb gave the light at approximately 

 70 cm. from the animal. The latter was a medium-sized adult. 

 Since the sexes respond similarly to light, no account was taken 

 of sex in this and the following experiments. Having deter- 

 mined the orientation of the animal by means of a 60 w. bulb 

 behind it, this bulb was turned off as the 25 w. light was flashed 

 upon it, from in front, striking the eyes of the animal so as to 

 make an acute angle with the axis of the body. 



Trial 1, Light 35° to left ; response to right. 



2, 15° ; animal stopped, wavered, and turned to right. 



" 3, " 70° " " ; animal stopped, then turned to right. 



" 4, " 60° " " ; response to right. 



5, 10° " ; animal stopped, moved forward, then to left (toward light). 



" 6, " 5° " " ; same as 5. 



" 7, " 3° " " ; same as 5. 



" 8, " 5° " right; animal turned to left. 



These trials show a tendency in the organism to turn away from 

 the light, the direction in which the turn is made depending upon 

 the' position of- the light and the angle at which it strikes the 

 eyes; there is a stronger tendency to turn to the left than to 

 the right, but this is overcome when the light from the left 

 strikes the eyes at an angle with the body axis of 15° or more. 



The same tendency to turn more readily to one side than to 

 the other is seen in the next series; though here the organism 

 turns more readily to the right. 



II. Another individual. Lights as in Series I. 



Trial 1, Light 10° to left, 36 cm. distant 



2, 

 3, 



4, 

 5, 

 6, 

 7, 

 8, 



35° 

 5° 



12° 

 5° 

 5° 



45° 



30° 



36 

 right, 36 



36 



70 

 left, 70 

 right, 70 



70 



Response to right, 



distant. Response to right, 



distant. Response to right, 



distant. Response to right, 



distant. Response to right, 



distant. Response to right, 



distant. Response to left, 



distant. Response to left. 



As in the first series, the organism turns away from the light, 

 either to the right or left, when light strikes it at an angle greater 

 than a certain magnitude, in this case between 12° and 30°. 

 When the light strikes it at an angle of 12° or less, the organism 



