404 WILLIAM L. DOLLEY, JR. 



directly below the center of the lamp. But since this did not 

 occur, it is evident that there must be changes of intensity of 

 light upon certain ommatidia coincident with every change in 

 position of the head. 



The fact that some butterflies with one eye blackened, when 

 placed in non-directive light, at times moved in a more or less 

 straight course, especially when tested twenty-four hours or more 

 after the eye was covered, also demands attention. In these 

 straightened courses, the movement is either controlled entirely 

 or in part by internal factors, or it is the result of a balanced 

 effort of two stimuli; one, light, tending to cause the organism 

 to turn in one direction, and another, the varnish, tending to 

 cause it to turn in the opposite direction. 



E. RELATION BETWEEN THE DEGREE OF CURVATURE IN CIRCUS 

 MOVEMENTS AND THE INTENSITY OF NON-DIRECTIVE LIGHT 



If the assumptions made by the adherents of the 'continuous 

 action theory' are valid, i.e., if orientation in organisms is depend- 

 ent upon the relative amount of light energy received by the two 

 retinas, and if the tension of the muscles controlled by the retinas 

 varies with the amount of light energy received, then the circles 

 made by animals with but one functional eye in non-directive 

 light of high intensity should have a smaller radius than those 

 made in light of low intensity, for the amount of light energy 

 received by the functional eye would be greater in the high in- 

 tensity than that received in light of low intensity, and, conse- 

 quently, the inequality between the amounts of energy received 

 by the two retinas would be greater under the former condition 

 than under the latter. 



This was tested in two experiments. In one, non-directive 

 light of two fairly high intensities was used; in the other, the 

 insects were first exposed to light of very low intensity (0.5 to 

 0.07 mc.) and then the intensity was gradually decreased. These 

 experiments were performed in the light-tight box previously 

 described. In the first experiment the lower intensity was pro- 

 duced by placing a 16 c.p. lamp over the opening of the box, and 

 by interposing resistance in the circuit until the intensity of this 



