THE ORIENTATION OF PORCELLIO TO LIGHT 



119 



turns toward the light in the definite turning movement that 

 ultimately carries it away from the light. 



The two series of trials just presented suggest a difference 

 in .the sensitiveness of the two eyes to light. Tests of each 

 individual by means of a light shining upon it from behind, 

 fully supported this view. The first individual was guided 

 without fail to the left when the light came from behind at a 

 "small angle to the right ; but the same individual did not respond 

 with such definiteness to light coming from behind at a similar 

 angle to the left. These statements will apply equally well 

 to the second individual, if the directions are reversed. 



III. Another individual, young, unpigmented. Lights as 

 before. 



response to left, 

 response to right, 

 response to right, 

 response to right, 

 response to right, 

 response to left, 

 wavered, then left, 

 wavered, then left, 

 response to left, 

 response to left, 

 toward light, then left, 

 response to right, 

 response to left, 

 response to right, 

 response to left, 

 response to right, 

 stopped, then to left, 

 response to right, 

 wavered, then to left, 

 response to left, 

 wavered forward. 



This series brings out the fact that although the individual 

 responds to light as an approximately symmetrical animal, its 

 reactions lose precision when the light rays fall upon it from 

 the front at very small angles (e.g., five degrees or less) with 

 the axis of the body. 



The following record of another individual bears directly 

 upon this point. Preliminary tests showed that this individual, 

 almost symmetrically sensitive to light, responded toward the 

 right a bit more readily than toward the left. A 60 w. Mazda 

 lamp was used, about 15 cm. in front of the animal, a given 

 number of degrees of arc to the right or left as the case might be, 



