RELATIVE STIMULATING EFFICIENCY OF LIGHT 



167 



covered which may influence the physiological state of the 

 organism and consequently the angle made in a field of light 

 composed of two horizontal beams crossing at right angles. 

 They are present stimulation and previous experience of the 

 organism. 



The effect of the first of these was demonstrated in the following 

 manner. A butterfly designated "21" was given 10 trials in 

 two beams of continuous light which crossed at right angles. 

 The illumination in one beam was four times stronger than that 

 in the other. The average angle made in these trials was 9.5 

 degrees (see fig. 5). After each trial the butterfly was allowed 

 to walk onto a piece of cardboard by means of which it was 



FIG. 5. Paths of a specimen of Vanessa (butterfly 21) showing effect of stimu- 

 lation on orientation in a field of continuous light composed of two horizontal 

 beams crossing at right angles. (Reduced by three-fourths). Illumination in 

 beam to left, 3.5 m.c. ; in beam below, 14 m.c. Figures above and to right, degree 

 of deflection in individual trials from line bisecting angle between the two beams. 

 "Plus" indicates deflection toward weaker light; "minus," toward stronger light. 

 Conditions in A and in B were identical except that before each of the trials in B 

 care was taken not to stimulate the insect, while before each of the trials in A the 

 animal was stimulated by being shaken violently in the hollow of the hand. 

 Note that stimulation caused the insect to react more strongly to the weak light 

 and to react very slightly, if at all, to the strong light in 7 out of 10 trials. 



carefully transferred to the starting point for a new trial so as to 

 avoid stimulation as much as possible. A f ter completion of 

 these trials the organism was given 10 more trials under the 

 same conditions, except that before each of these triads the insect 

 was stimulated by being picked up in the fingers, placed in the 

 hollow of the hand, and shaken violently. The average angle 





