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WILLIAM L. DOLLEY, JR, 



made in these 10 trials was +22.4 degrees. This shows very 

 clearly that mechanical stimulation may greatly affect the 

 deflection in continuous light from two sources. Here "plus" 

 indicates deflection toward weaker light and "minus" toward 

 stronger light. Where used elsewhere in this paper "plus" 

 indicates deflection toward stronger continuous light or toward 

 intermittent light. 



Stimulation also may affect the angle made in intermittent 

 light. As is shown in figure 6, butterfly 21 was given 7 trials in 

 intermittent light of a irequency of interruption of 5 per second 

 by the method described previously. Care was taken, as hi 

 the tests in continuous light, not to stimulate the annual. The 



FIG. 6. Paths of a specimen of Vanessa (butterfly 21) showing effect of stimu 

 lation on orientation in intermittent light. The field of light is composed of two 

 horizontal beams of equal illumination, 3.5 m.c., crossing at right angles, the light 

 in one beam being continuous and that in the other intermittent. (Reduced by 

 three-fourths). Intermittent light is of frequency of interruption of 5 per second 

 produced by disk with one-fourth removed. Other explanations are the same as 

 those given in the description of figure 2. Conditions in A and in B were identi- 

 cal 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 vigorously stimulated 

 by handling. Note that stimulation caused the insect to react strongly to inter- 

 mittent light and very slightly, if at all, to continuous light in 6 out of the 7 trials 



average angle made in these trials was 16.4 degrees. Imme- 

 diately afterwards the butterfly was given 7 trials under the 

 same conditions, but before each of these the insect was stimu- 

 lated by being shaken violently in the hand. The average angle 

 made in these 7 trials was +27.4 degrees. This test shows clearly 

 that stimulation may also greatly affect the angle made with 

 the rays of light if the light in one of the beams is intermittent. 



